Relay Phobia

I have a phobia about relays and I really don't understand why. In this age of solid state switching there is something messy or unwholesome about having electro-mechanical devices scattered throughout my station. 

Is my attitude entirely counter to the evidence or is there anything to support my fears? 

It is good that relays are as reliable as they are since they are everywhere in a modern ham station, more than you might realize. Yet they can and do fail. This is mostly due to two factors: quality and abuse. A little knowledge can help us to get the most from relays. Technology has not advanced so far that relays can be avoided.

As you might guess from my irrational phobia, I am not an expert on relays. I had to learn more about them to assuage my concerns and to choose and use relays in my many home brew projects. 

They are used in my station to switch:

• DC and AC power
• Antennas
• Antenna switches
  
• Antenna direction and stack controls
  
• Matching networks
• SO2R audio and keyer
  

Many of those are home brew projects. I even have relays that control other relays! Relays are common in commercial equipment to control power, route transmit/receive RF, inter-stage switching, ATU, BPF, antenna ports and more. One malfunctioning relay can ruin your day or contest. 

It's that critical role they play and the risk of failure that stokes my fears. I trust that relays are appropriately selected and employed in commercial equipment. This is not necessarily the case. One famous example is the Yaesu FT102. Every relay in that transceiver had a short lifetime and is responsible for far too many of these otherwise excellent rigs ending on the trash heap. 

Mine eventually landed on a flea market table. It sold for a low price that was, unfortunately, fair value. I could have salvaged the rig with replacement relays, which are available, but I deemed it not worth the trouble. It was a great rig in its day but no more.

Returning to my phobia, my lack of knowledge and therefore trust of relays leads to odd behaviour. For example, I have an irresistible urge to idle all the relays in my extensive antenna system when I step away from the shack for more than a few minutes. I don't yet have such a feature in my station automation software so I have move the rig to 6 meters to idle the 2×8 antenna switch and manually deselect directions and modes for the stacks and several other antennas.

Is this a feature I should build for my station automation system? Do relays deteriorate when they're energized? Is it better to leave them energized to avoid turning them off and then on again when I return to the shack? Relays do have lifetimes based on these metrics and many others as well. Let's see what the data can tell us.

Above is an extract from an Omron G2RL datasheet -- you may have to click on it to make it readable. It seems fairly typical of small, sealed relays. A fact that pops out quite clearly is that the mechanical life of the relay is far greater than the life of the electrical contacts. The mechanical lifetime is so long, even when switched continuously at a rate of over once per second, that it is effectively eternal in typical ham use.

The shorter electrical lifetime spec is misleading since it is for the rated contact voltage and current. When these are lower the lifetime increases. The chart at right is also from Omron. Clearly there is a benefit from choosing relays with higher ratings than what will be experienced. Better yet, by avoiding hot switching the lifetime can be greatly extended.

By avoiding hot switching and using high current contacts the lifetime is sufficiently extended that there should be little concern for the reliability and durability of the relays in my home brew projects and the commercial products I use. Relay lifetime can easily exceed my lifetime.

Hot switching can be avoided or mitigated in well designed equipment. Measures include:

• Software features to prevent hot switching of antennas. I have this feature partly implemented in my home brew station automation system.
  
• Sequencing of circuits so that relay closure occurs before current is applied, and the relay opens only after the current is cut. Sequencing of the input and output port relays is standard for the ports of high power amplifiers and in V/UHF systems with mast mount LNA (low noise amplifiers).
  
• Step-start relay coil with a higher than nominal voltage so that closure is rapid. Arcing and contact wear are thus reduced when hot switching high voltage or current is unavoidable. 
• Sequencing or ramping motors and other devices with a high initial current. In our shacks the most common application is high power motors in rotators such as prop pitch motors.
  

By avoiding hot switching entirely you can achieve relay lifetimes of well over 1,000,000 on-off cycles. The TE application note I linked to has a lot more on the topic worth reading, including contact materials, arc mitigation and other recommendation for selecting relays. 

An amusing story a friend told me related to the fourth bullet above was using relays to switch a prop pitch motor. Depending on cable resistance, the motor starting current can be 20 A. One day the contacts fused from excess arcing and he didn't immediately notice that the motor hadn't stopped. Luckily the damage limited to a shredded coax rotation loop. 

Now he sequences the power by first energizing the high current DC relay and then the low current AC mains of the 24 VDC power supply. I plan to do the same with my prop pitch motor; currently, I do the sequencing with manual switches.

If you must switch transmit level RF and proper sequencing cannot be guaranteed, or the RF voltage is high, there is the option of vacuum relays. They are expensive, new or used. They can be found on many amplifiers. They are also useful when switches are needed at high impedance (high voltage) points of an antenna. The contacts can still be damaged by excess arcing but they should not oxidize.

The photo at right shows the effect of arcing on relay contacts. This relay has failed, will fail soon or the contacts might even fuse with continued abuse.

The relay contact protection measures described above are fine for high power switching but not necessarily for small signal switching. You might think that small signal switching is not worth worrying about, but it is. This is as true for relays used in receive arrays and control systems as it is for RF relays that must work well for both transmit and receive.

Contacts oxidize or undergo chemical changes due to current flow and micro-arcs. Open relays will accumulate grime. Sealed relays, like most of those I use (see above), are largely immune to the latter. There are mitigation measures described in the linked TE application note. However, placing components across the contacts that are suitable for DC and 60 Hz AC, it is not appropriate for RF applications.

The easiest way to deal with contact problems in sealed relays is to periodically switch them under load. In this case arcs are our friends. They burn off unwanted oxidation and other unwanted chemicals and restore low resistance conductivity. There is micro-arcing even for the small DC currents switched by the relays in my automation system.

Antenna relays that are usually not hot switched can be periodically switched while transmitting to clean the contacts. Typical power levels commonly quoted to do this range from 20 to 50 watts. Cycling 10 under load may be sufficient. Don't try this with your big amplifier! Those arcs can rapidly damage the contacts. In any case, amplifiers with fault protection will quickly go offline when an arc occurs. 

I occasionally did this when I had I was manually switching antennas, modes and directions and I suspected a problem. It didn't hurt to do it even when the problem might be elsewhere. In my case it always turned out to be a relay in the transceiver or amplifier. I can't do this with the automation system since it doesn't allow hot switching. Instead I would have to add a "cleaning" feature or temporarily connect the control cables to the manual antenna controller, which I keep as a backup. But I have yet to bother since there have been no recent relay problems to resolve.

Returning to the matter of relays used solely for receiving systems where the RF level is always small, dynamic cleaning methods don't work well since there is no arcing. If the contacts corrode there may be little remedy except replacement. Contact design and coating are particularly important. For example, using multi-pole relays in parallel for contact redundancy. Gold plated contacts are another possibility. 

An increase of contact resistance can weaken reception, especially at the low impedance 50 Ω side of the receive antenna switching circuit. Contact resistance will likely get worse over time unless the contacts can be cleaned. Sealed relays protect against environmental effects but also make it impossible to access the contacts to burnish them. I have had relay contact problems in my rebuilt Beverage head ends. Cycling the relays has served to reserve intermittent problems until now. It wouldn't surprise me if I eventually have to replace the reed relays in the remote Beverage switch (see below).

A trickle DC current can serve to wet the contacts to keep relay contacts clean in lieu of arcing. Receive RF is far too weak on its own for contact wetting. Combined DC and RF is most commonly found in bias-T circuits where the coax carries both, with signals combined on one end and separated on the other. This is done to eliminate a separate control cable run to the relays at the antenna end of the coax.

The only place in my station that I use a bias-T this is to reverse direction of my three reversible Beverages. There is a separate control cable to the remote Beverage switch, with one line putting +12 VDC onto the coax to the active Beverage via a bias-T circuit. The DPDT reed relays in the remote antenna switch thus carry both DC and small signal RF to the bias-T in the Beverage head end.

Does the reversing current help keep the reed relay contacts clean? I don't know. I've never had a problem with the contacts except when lightning struck the Beverage system last year. Those contact arcs destroyed the relays.

Contact wetting is in conflict with a bit of ham lore. There is a common belief that a DC bias on relay contacts can worsen contact resistance over time. Certainly I've seen contacts develop problems over years of use but I doubt whether that is the reason since it runs counter to my understanding. I don't know the truth of the matter so I thought to mention it since may encounter it from time to time. There could be a galvanic effect but it may be nothing more than a lack of arcing to clean the contacts.

Wrap up

Solid state switching has its own challenges despite not have moving parts and physical contacts. When employed correctly, relays will last a lifetime. There are inexpensive relay boards for Arduino, Raspberry Pi and similar controller that save the trouble of designing and building solid state control circuits. For switching high power RF, relays remain the easiest and most cost effective solution. That could change in coming years

In summary, relays are great. It's a matter of choosing suitable devices and following best practices to keep them healthy. They're inexpensive enough that replacing them isn't a great burden. 

My relay phobia is unjustified.

You Don't Need an N Connector

N and UHF connectors have their pros and cons. The same is true of other connectors, be they BNC, SMA, F, DIN and the many other RF connector series. I use them all, by choice or by necessity when present on equipment I use. 

There is no one correct connector. Each is designed to meet different engineering requirements. Connectors themselves come in many varieties -- chassis mount, PCB mount, screw on, solder, crimp, clamp, mechanical -- to suit different environments and applications.

The majority of hams use UHF connectors for RF connections. They are ubiquitous on HF transceivers, except those with very small enclosures. They perform well, are inexpensive and easy to use. 

V/UHF operators tend to use N connectors to avoid the impedance "bump" of UHF connectors that can be problematic at higher frequencies. UHF connectors do not preserve the Z₀ of the coax throughout their lengths, whereas N connectors do. There are different N connectors for 50 Ω and 75 Ω systems. There is no such differentiation for UHF connectors.

The reason for the impedance discontinuity in UHF connectors is that there is a short air gap between the end of the coax and from the mechanical structure of the termination, in particular the insulator surrounding the centre pin. The dielectric constant and conductor separation vary over that span. We have effectively inserted a short transmission line with a different nominal impedance. Mechanical design takes priority over impedance performance in UHF connectors. The impedance bump can be worse for coaxes smaller and larger than RG213. 

A typically quoted value for the bump is 30 to 35 Ω, which is believable from inspection of the transmission line equation for coaxial cable. Let's use the lower value even though there are differences across manufacturers and adaptors for large and small coax diameters. I'll further assume that the length of the discontinuity is 1 cm (10 mm or 0.4"), with a VF (velocity factor) of 0.7. Choosing these values should simulate a worst case for PL259 (male) UHF connectors.

I used SimSmith to insert a 1 cm long section of 30 Ω coaxial transmission line between a 50 Ω generator and a 50 Ω load. You can see that the effect is negligible at 50 MHz. It is marginally significant at 144 MHz and notable at 450 MHz. Of course there will be more than just one connector in a transmission line, with one at the rig, one at the antenna, two at each coaxial joint (e.g. barrel connectors) and two at each intermediate device such as antenna switches. The one at the antenna is usually of no interest since the feed point matching system typically compensates for that connection. The same is true of the transmitter or tuner at the generator side of the line.

SWR does not sum arithmetically. You can't simply add up the fractional quantities to discover the net SWR (mismatch) due to multiple connectors. That is, two connectors that exhibit a 1.05 SWR in a 50 Ω system when properly terminated do not give an SWR of 1.1. In select cases, insertion of a short 30 Ω transmission line can improve the match.

In a real system there are many variables that a simple analysis like mine cannot possibly contain. In each system you'd have to measure the complex impedances and coax lengths for each band of interest, along with the major effects of the load mismatch (no antenna is perfect!), generator action and other factors. My SimSmith model is illustrative but not universally applicable.

My usual recommendation to those who ask is to avoid N connectors from 160 to 2 meters. The performance impact of using UHF connectors ranges from negligible to modest, and is usually dominated by the antenna impedance, which is usually nowhere near 50 + j0 Ω. Other factors such as variation in coax impedance by manufacturer, application and age have impacts greater than that of the bump due to UHF connectors

None of this is a criticism of N connectors in general. It is reasonable to ask: why not use N connectors? Why not sweep away the uncertainties by avoiding UHF connectors wherever feasible? There are good reasons to prefer UHF over N connectors other than that of the dreaded impedance bump.

Pieces

The typical N connector has several components. It is an unwise ham who breaks open the package without a plan. It is easy to lose one or more of them, especially the centre pin.

I opened one of my bags of used N connector parts so you can have a look. These are 50 Ω connectors that were salvaged from old coax. Most of the pieces are present, and I have other bags with different assortments. I have fewer pins than bodies, which is annoying. 

The main gasket is cut in two when first assembled, but they can be reused if you are very careful. Alternatively, do an especially good job weatherproofing the assembled connector. The gaskets in a pristine N connector provide good weather protection, but don't depend on it. Protect them as you would a UHF connector for reliable long life. Braided coax wicks moisture and will soon degrade.

Used N connectors can be frustrating unless you have a good eye for the slight size difference between 50 Ω and 75 Ω pins. I am not so worried about the impedance than I am about trying to mate mismatched pins. It doesn't work and you can't force it. Force fitting a male 50 Ω pin into a 75 Ω female pin will destroy it. UHF connectors don't have that risk.

Notice that I've shown soldered connectors. That is only for the centre pin since the braid is mechanically bonded when the external nut is tightened. However, you must be precise with the dimensions of the exposed braid, dielectric and centre conductor or the braid will be loose. It's a problem I've encountered many times with connectors I've assembled and with those that have followed me home.

A related concern is the position of the centre pin. Get the dimension wrong by just 2 mm and the male and female pins either won't make solid electrical contact or will bottom out and bend when the connectors are joined. Again, this can't happen with UHF connectors.

There is another challenge with pin alignment when using RG213 and similar polyethylene dielectric coaxes. The braid can slide over the dielectric due if too much of the coax weight is taken by the connector. The same will happen by weather induced thermal expansion. It takes little movement to have a connector suddenly fail in the middle of a winter contest due to lost electrical contact or arcing. It is more common than you might imagine.

I had to deal with improperly aligned N connectors on a fellow ham's tower last year. If you have trouble properly preparing the coax and assembling an N connector on the ground, well, it's far worse doing it up in the air. The cables with the poorly aligned connectors were cut down for repair on the ground and then lifted back onto the tower and tied down to ensure there was no weight (stress) on the connectors. One of them failed again a few days later. This time we decided to cut it off and friction fit a UHF connector to the coax. Half a year later it's still working despite not being soldered.

Contact Area and fragility

Compare the size and area of the contacts in UHF and N connectors. You can see examples in pictures above and below. The small centre pins are particularly fragile and misalignment when joining connectors can bend the pin and distort the gripping flanges of the female pin. Pins of 75 Ω connectors are smaller and more fragile. Pressing a male 50 Ω pin into a female 75 Ω pin can easily destroy the female pin. It will never grip well after being overspread.

Alignment is especially problematic with solder connectors on flexible cables with a stranded centre conductor (e.g. RG213). Getting the pin centred must be done manually. A small deviation off centre can easily damage the pins when joining connectors. The hole in the female pin is very small and easy to miss since once your view of the pins is hidden when the connectors are brought together. You must be careful and go by "feel" alone.

Just 1 mm of linear insertion error due to the pins projecting too little or too much results in inadequate contact or bending, depending on the direction of the error. In the former case, the connection is unreliable either due to high resistance or arcing with high power. In the latter case the constant impedance of the N connector is lost and there can be a short or arcing when the pins are bent. The outer spring flanges of the male connector are usually not a problem because they are stronger and their position fixed by being bonded to the connector body. 

Threading ensures proper positioning of the male flanges against the body of the female connector. Since the threads are so fine -- ⅝"-32 UNEF -- crossing threads is easy, which can damage the threads and the connector flanges. Damage is easier with hard line coax since it is more difficult to manipulate the cables to ensure they're properly aligned when the threads are engaged. On a UHF connector, the large centre pin engages first and guarantees proper alignment of the contacts and thread engagement.

Above is a splice between a male N connector on buried LDF4 cable to my 80 meter vertical wire yagi and a female N on the long LDF5 run to the station. This week I discovered that the flanges are making intermittent contact, and that is the reason for the antenna's failure this winter. My guess is that I bent something slightly when struggling to align the connectors for thread engagement. I have it working again but I may replace one or both connectors this summer just to be certain that it survives next winter.

The centre pin and female spring flanges on a UHF connector are large and robust in comparison to those of N connectors. They are not easy to damage, yet there are hams who manage to do it anyway! If the flanges are overspread they can often be fixed, at least in an emergency, using a small flat blade screwdriver to bend them inward. The large contact area of the centre pin and threaded shell assure good electrical contact even in cases of minor damage. 

There are no gaskets in a UHF connector so it is mandatory to use external weatherproofing. Moisture infiltration will cause corrosion, and that leads to high resistance and arcing despite the large contact area. Never leave a UHF connector unprotected outdoors, even temporarily. Weatherproofing it after rain, snow or morning dew (condensation) will trap the moisture inside.

Alternatives

All is not doom and gloom! There are N connector styles that largely eliminate the problems of exact dimensions and pin alignment. These are so good that there is no reason to succumb to the temptation to buy or reuse solder N connectors. But it can be expensive if you have a lot of connectors in your station, as I do.

I am pretty well forced to use N connectors for the thousands of feet of Heliax in my station. They can be found surplus in quantity and at very attractive prices. If you know someone in the commercial wireless business you can often get them for free by dumpster diving. The Andrew connectors are very robust and I've had better than a 90% success rate reusing scrounged connectors. 

UHF Heliax connectors are rare. Newer commercial installation often use 7/16 DIN connectors, and they are not yet showing up in quantity on the used market. The DIN connectors are larger and hardier constant impedance connectors. The ring of thick flanges on the female 7/16 DIN connector in the picture at right are for the centre pin, not the outer conductor!

I have several new and used DIN connectors in my stock. They are useful for splicing sections of Heliax but not at the ends of the feed line where you'll likely need an adaptor. I have just one N-to-DIN adapter in my stock and it wasn't cheap. I have never shopped for a 7/16 DIN connector for LMR400 to connect to Heliax DIN connectors. If they exist they are certain to be expensive.

These are my most recent flea market finds. A paid a modest price for these used LDF5 Heliax connectors for the convenience of just picking them up and walking away. Dumpster diving is free but there is effort involved. I've already started giving them away to friends. I have enough on hand and more will undoubtedly appear in the coming months and years. Surplus and "reel ends" Heliax is available at good prices if you are fortunate enough to have contacts with commercial tower service companies.

Adaptors for joining N and UHF connectors are common and inexpensive. The kind shown in the picture are often found surplus for a dollar. I also buy the less common female-to-female adaptors for when the Heliax connector is an N male.

I use many of these adaptors on the tower and on the ground to interconnect RG213 and LMR400 running to antennas and antenna switches. One good feature of adaptors is that the N side is always perfectly positioned. Alignment is never a concern.

An N connector I particularly like for LMR400 coax is one with a "captivated" centre pin. It is also advertised as a clamp connector. Like the adaptor, the pin is fixed and can never slide out of alignment. On the inside of the connector, the coax centre conductor is press fit into flanges that grip it from all sides. The outer conductor is held in the usual manner, be it by a nut or crimp. There is more latitude with dimension errors since there is room for axial motion within the flanges.

Fitting the coax can be frustrating if you don't closely follow the installation instructions. The centre conductor must be chamfered with a file so that it can fit inside to lift the flanges as it is pressed in. Without the chamfer the conductor won't fit and no amount of pressing will help. The coax must be very straight for this operation. Any deviation must be corrected since there is little wiggle room to align it with the flanges once it's inserted, and you must do it blind.

Captivated connectors are not cheap. I purchased several at a good price when I was first building this station. I thought it would be easier and cheaper than using UHF connectors plus an adapter to the Heliax N connectors. I was wrong on both counts so I stopped using them. However they are excellent connectors and they are in wide commercial use for their reliability. 

I couldn't find a good picture of an LMR400 captivated connector online so I took one of a single piece Heliax connector in my stock that uses a captivated centre conductor. The difference is that the Heliax centre conductor is hollow so the flanges grip the inside rather than outside of the conductor.

There are restrictions on the application of captivated connectors. They fit one and only one type of coax. You must buy the correct connector for the coax. Captivated connectors don't work on coax with a stranded centre conductor like RG213.

Two-piece Heliax N connectors are easier to install correctly than those for LMR400 or RG213. One reason I like using LDF5 in my station is because the cable and its connectors are widely available on the surplus market and the connectors are easier to install than on smaller Heliax (LDF4) and larger Heliax (LDF6 and LDF7). All it takes is a hacksaw, knife, file and wrenches to make a perfect termination.

More alternatives

Does all this information make your head spin? Do you really hate fooling around with coax connectors, but you still would like N connectors? There are many companies that will fit any length of coax with the connectors of your choice as a complete custom assembly. The prices I've seen are reasonable, though more expensive than doing it yourself. It is also no guarantee against future problems. The choice is yours.

With regard to UHF connectors, you can also use commercially prepared cables. Many fear damaging the coax through excess soldering heat and cold solder connections. If you do it yourself, I recommend a silver plated connector which takes solder with less fuss and therefore a lower risk of damage. Some like K3LR solder the braid to the outside of the connector body. But if you do it wrong the shell won't slide into place. The impedance bump is longer with this method so it is best to avoid it on VHF systems.

There are many inexpensive UHF connectors on the market that do not meet spec and are difficult or impossible to use. Buy from a supplier with a reputation for quality. If soldering is too much to handle, use crimp UHF connectors. Cost for the crimp tool is worth it when you have many connectors to prepare. You may be able to borrow a tool from a friend if you only have a few connectors. 

I stick with conventional silver plated connectors from reputable dealers, soldered through the holes, and I rarely go wrong.

Some hams convert Heliax N connectors to UHF. You can do this because the exterior threads are the same for both connector series: ⅝"-32 UNEF. See the proof in the above demonstration. I prefer the risk of future mechanical woes of Heliax N connectors over the work to do the conversion. Consider it food for thought.

Mythology

In addition to the myth than UHF connectors do horrid things to your SWR at VHF, and even HF, there are others. Two examples are that N connectors can't handle a kilowatt or a high SWR. Both are untrue, or at least not all that different from the performance of UHF connectors.

If you ask a ham about coax connectors you will almost always get an answer, and it will be delivered with supreme confidence. Sometimes the answer will be correct. Dig deeper by asking why and what their experience is with those connectors. You should be able to quickly spot the pretenders. Be especially wary of listening to those who tell you what you want to hear.

Uncertainty leads to extreme behaviour: aiming for perfection or taking an anything goes approach. The first can be a poor investment of time and money. The second is asking for trouble. Make decisions based on solid knowledge, not mythology.

Wrap up

My guiding philosophy can be summed up pretty simply: use UHF connectors when I can, and use N connectors when I must.

Unless you have a particularly good reason to use N connectors you are better off sticking with UHF connectors for HF and VHF. My reason for using N connectors is all the Heliax in my station. If not for that there would little need to deal with the many challenges of N connectors. 

Most hams don't need N connectors.

Spring is Coming

The title is an unapologetic riff on the "Game of Thrones" tag line: winter is coming. It's appropriate. With our cold and snowy winters, most tower and antenna work is halted for several months. Winter is a time to operate and work on indoor projects. As the snow thaws and the temperature rises in early spring, there is a looming sense of dread despite the more clement weather.

Sure, spring and summer are glorious times, which I love, but that's not all. The station develops problems during the harsh winter months when it's too cold to deal with them. The list of new projects also grows. Springtime signals a rapid transition from relaxation to frenetic activity. Insects wake up and hunt for victims. There are disease-carrying ticks, black flies (the kamikaze pilots of the insect world), and the slower moving but voracious mosquitos. They must be braved while working down the long to-do list.

My lawn is very large and there is much to be done in the spring before the grass (and weeds) begin their growth spurt. That alone will consume many days and it all has to be done in April. What I can't complete will have to be deferred to October when the growing season comes to an end.

In May the hay starts its serious growth and I am largely kept out of the fields and away from major tower projects. The growing hay is difficult to work in and there is a limit to how much of it I can mow to make room for that work. The hay is also where ticks lurk and wait for passing deer and careless hams. 

Hay season from late May to early August is prime sporadic E season. I spend some of that time to chase DX on 6 meters. On days when the band is closed I am often found in my workshop building antennas and other contraptions, or out cycling or other summer activities. Late summer and autumn is the second and longer period for tower and antenna work.

A fox almost blundered into me while I standing on the rock wall while working on the overhead cable run. I heard noise in the leaf litter, looked down and it looked up. I'm not sure which of us was more startled. The fox bolted. It looked back a few times as it went, wondering what I'd do. I simply shrugged and got back to work.

We had an ice storm a week ago. A large tree limb fell, luckily away from the overhead cables. This is another peril of spring: lots of precipitation when the temperature hovers near 0° C. Antenna damage was minor (one of the Beverages) and quickly repaired. Unlike in other storms, the vulnerable rural distribution system survived and we had no power outage at all. The storm damage and power failures were worse elsewhere.

By the time the fox arrived the fallen tree had been removed. I was on the wall finishing the work on the overhead cable supports. It was well supported when winter swept in so there was no urgency. This week I finally cleared away the old supports. The new post gingerly winched out of the ground. It had been pushed down 6" by cable tension. It must have slipped off the wood plank without my noticing.

With the winch and a second steel post, I lifted and set it on the steel pin and bolted it for lateral support. I couldn't do it in the winter so the old post occupied the support frame. The job took a day and a half, which is 3 times what I estimated. There were complications due to the need to support the cables during the work.

Winter took its toll on a couple of antennas. The 160 meter vertical developed an intermittent during high power transmissions. Operating on 160 meters without high power pretty well kept me off the band for a few weeks. All I could do in the cold was to quickly test the many mechanical connections, twice. This turned an intermittent problem into a permanent outage. Once the weather warmed up I did a more thorough investigation.

It turned out to be a wire that was squeezed out from between a pair of washers and was barely contacting the capacitors of the gamma match. As noted at the time, the voltage at the gamma capacitor is very high and prone to arcing. It was easy to fix once found.

The problem with the 80 meter yagi could not be found at all in the cold weather since several key connection points to the switching system and radials were encased in ice at the base of the driven element (tower). That has all thawed during this week's unusually warm weather. I will be out there in the coming days to work on it. I am hopeful that it is something simple.

During the cold of winter, tower jobs are limited to those that don't require fine work. Climbing in winter isn't the problem, it's having to take my gloves off to fiddle with hardware and wires. Once your fingers are chilled they don't warm up too quickly and it's cumbersome to continue work and then climb down with stiff and partially numb fingers.

In the coming days and weeks there are several jobs on my list that I will attend to. Others are less urgent.

• Inspect towers, antennas, wires and mechanical fixtures; this is a semi-annual chore
• Inspect and make temporary repairs to the mast coupling system to the upside down prop pitch motor rotator for the 15 and 20 meter stacks; I'll have to replace it eventually but hopefully not this year
• Complete modifications to the pulley system driving the direction pot for the same prop pitch motor; despite the high tension there is still occasional slippage that requires re-zeroing the indicator
• Build, install and test new capacitance hats on the driven element of the 3-element 40 meter yagi; if they do well I hope to undertake the far more difficult job of replacing the hats on the reflector and director elements (see early construction phase above)
  
• Ground all the Beverages in preparation for lightning season; this will not be an inconvenience since I must roll up the radials of the 160 meter vertical in preparation for the summer haying
• Find and install better straps that bind the mass of cables to the overhead cable run; the new rubber straps I installed in the fall rapidly deteriorated, while the far older ones are fine: quality matters (see below right)
  

With all of these jobs, yard work and other activities there has been little time for operating. As I write these words, I've made less than 10 contacts this month! I usually monitor 6 meters (50.313 MHz) when I'm busy elsewhere, but even that has been pretty quiet due to the low solar flux. We are in the doldrums between March equinox-enhanced north-south propagation and the start of sporadic E season a few weeks hence.

There are also a growing number of requests from friends to help out with their tower work. That doesn't happen as often as it did years ago with elderly hams holding fast with what they have and not undertaking new projects. I help out where I can. Others have also been making their lists in preparation for spring warmth and they reach out to me.

With all of the maintenance work to be done and the many new projects in my 2023 plan I expect to stay busy this year. If you enjoy QSO parties, please come out for the Ontario QSO Party on April 15 and 16. I will again be hosting one of the bonus stations so my presence in the contest is guaranteed.

Auxiliary Antenna Switch

Woe to those with too many antennas! No, not really, but it does create a switching nightmare that isn't present in most stations. I have finally reached the capacity of the switching hardware in my station.

The core of my switching system is the 2×8 Hamplus antenna switch that is at the base of the closest tower. Putting it there means there are only two coax runs into the house, one for each operating position. Eliminating that multitude of coax runs into the house simplifies cable management and keeps the holes in the wall quite small. 

The cost of the remote switch is ~18 control lines from the shack to the switch (3 × Cat5), weatherproofing (and insect-proofing) and occasionally having to stomp through the snow drifts for mid-winter maintenance. Few contesters of my acquaintance do it the way they have. They prefer staying indoors to work on their switching systems.

I've been able to stay within the 8 antenna capacity of the switch until now mostly by luck. I freed one port when I moved the VHF antenna (6 meters) to a separate run of Heliax into the house. The Acom A1500 amplifier has 3 antenna ports, and I do the switching there. But the 6 meter antenna can't be accessed by the other operating position unless I add an antenna switch inside the shack. There is little point since the second station's L7 amp doesn't have 6 meters.

When I add a 2 meter antenna, I may switch them at the top of the tower with a remote switch. I have no great need to access both antennas at the same time. How I switch the coax within the shack will depend on what I settle on for 2 meter equipment. For now it is enough that I have removed VHF antennas from occupying ports on the 2×8 switch. 

Before installing the additional transmission line, I could plug either the 6 meter or 160 meter antenna into the 2×8 switch. I did it once in the spring and once in the fall. It's good that I no longer have to do this since 6 meters has become a year round band with the rising solar flux. I am also investigating methods to make the 160 meter vertical a year round antenna rather than having to roll out and roll up the radials before and after the winter season.

The addition of the 80 meter inverted vee spells the end of seasonal port swapping as a viable strategy. The 80 meter vertical yagi had to be disconnected. That's not a problem right now since it developed a fault this winter and isn't working properly. But I'll fix it soon and I need an antenna port to plug it into.

The 8 ports are currently for: 160, 80, 40 (2), 20, 15, 10 and the TH6. The time had come to build auxiliary antenna switches for 80 and 40 meters. There is rarely a reason that more than one antenna for these bands would be in use at the same time. By freeing up a port from the two allocated to 40 meters (3-element yagi and XM240) I can use it for another multi-band antenna or perhaps antennas for the WARC bands, when I have them. 

One antenna switch port per contest band makes it possible to place single band high power BPF at that point in the switching system. No matter which antenna is selected for each band, the BPF will be the correct one. That can greatly simplify use of BPF since no switching is required. I am happy with my 6-band switched low power BPF and there is no plan to spend big on high power BPF.

Hardware

I used the smallest sheet metal aluminum enclosure that would comfortably accommodate all the parts and leave finger room to manipulate the connectors. Small size keeps the lead lengths short, and that minimizes impedance "bumps".

There are 4 different styles of UHF chassis sockets. I used what I had, and one I had to purchase at a local flea market. Extra holes were drilled to increase the number of sheet metal screws. That is to improve the seal against water and insects. There is no electrical reason to do that at HF; the wavelengths involved are too long to "leak". I was sloppy about it but there are no bonus points for attractiveness!

The +12 VDC control line terminals are #4 screws through plastic flanges that isolate the screw from the chassis. It's adequate and avoids the trouble of mounting a multi-conductor connector of some kind to the enclosure.

The 4 antenna ports point down for additional weather protection. The angle bracket on the other half of the enclosure is for screwing the switch to a wood panel alongside the 2×8 remote antenna switch.

There are no surprises inside the switch. AWG 18 wires carry RF. The SPST relays are positioned to minimize the lead length. Solder lugs ease wiring of the relay coils and suppressor diodes (1N4007). The relays are mechanically supported by the RF wires. The TE System high current relays are used in antenna switches throughout my station. They easily handle a kilowatt provided the SWR is not too high and hot switching is avoided.

Performance measurements

This is the kind of switch that hardly rates testing beyond a continuity test with the relay turned off and on. RF at 40 and 80 meters is very forgiving of sloppy layout and wiring. Nevertheless, it is worthwhile to take a few measurements for peace of mind and to see how it does at higher frequencies. I will likely need one or more similar auxiliary switches for the high HF bands and VHF as I continue to add antennas.

Testing the switch does not require a 2-port VNA when you have an accurate single port antenna analyzer. Two ports to measure insertion loss is pointless for this circuit, and port isolation is likely to be quite small. There is no requirement for high isolation between the antenna ports of each switch since only one of those antennas is used at a time. High isolation is almost certain between the two switches at low HF frequencies. I considered and rejected putting a shield between them.

A sweep of the SWR from 2 to 30 MHz is about what I expected. At 30 MHz the impedance is approximately 52 + j3.5 Ω. This is about j2 Ω higher than the 50 Ω load alone. That is due to the inductive reactance of the internal wiring and relay. Both ports of both switches have identical impedance curves(within measurement error).

The impedance at 50 MHz is higher at about 53.5 + j5.5 Ω. The 1.15 SWR is low enough for most applications. I experimented with TLW to design an L-network that would compensate for the stray inductance. As for the 10 meter stack switch and its longer wires, a shunt capacitor is sufficient since the calculated series L is no more than 0.05 μH. A value of between 20 and 25 pf works well to correct the small mismatch on both 10 and 6 meters. Addition of the capacitor hardly disturbs the match at lower frequencies. 

I'll eventually want a switch to share one run of Heliax on 6 and 2 meters. Compensation for the stray inductance would be needed at VHF even if I make the switch more compact with less stray inductance since the path through the relays can't be shortened. The present switch for 40 and 80 meters needs no compensation for excellent performance.

Software

Port sharing requires additional conflict management in the recently completed station automation system. The Arduino software and switching software already has 8 auxiliary control lines for controlling devices such as this. Each antenna has pair of values specifying the port on the 2×8 antenna switch and auxiliary control line (or none). However the Arduino software does not yet prevent conflicts. That job is left for the hardware lockout in the 2×8 switch.

The UI (user interface) software running on the PC has been enhanced to check for port conflicts. If another radio is using the same port as that for a selected radio, the antenna is unavailable. In almost all cases this should only occur with multi-band antennas since, for each port with two or more antennas, those antennas are for the same contest band. 

Antenna selection for mono-band antennas is by auxiliary switch, like the one described in this article, or stack switch (currently only for the 10, 15 and 20 meter stacks). In a contest there would rarely be a port sharing conflict for radios on different bands.

Installation

The auxiliary switch has been installed and connected to the 80 meter port of the 2×8 antenna switch. The photo shows it mounted under the rain and snow shield before weatherproofing was completed. Both 80 meter antennas -- the inverted vee and the vertical yagi -- are connected to the switch. 

The control lines are not yet connected so only the inverted vee is currently accessible -- I made it the "default" for the time being. I used a permanent market to label the NC (default) port and the NO port, corresponding to the relay contacts. The letters are barely visible in the photograph.

The software and hardware additions to the automation system are in place and partially tested. Final testing has to wait until I patch the auxiliary switch Cat5 cable to one of the spare cables running to the tower base. That job will be completed in the coming days now that warmer weather has finally arrived. I will only take the opportunity to diagnose and repair the fault with the 80 meter yagi. The 40 meter antennas will be moved to the auxiliary switch later this month.

Band Slot Fatigue

What is the meaning of life? Too pretentious? How about: what is the meaning of amateur radio? Lest you imagine that this will be a sad philosophical tract and stop reading, please stay with me for a moment.

Each of us has motivations and interests that spur us to build stations, operate and relish achievements. At the top of my list are contests, DX and 6 meters. For others these might be AM, portable operating, EME, public service and much more. As the years pass, our interests change. We may abandon the hobby for a time (as I did) or we may increasingly focus on one particular interest. There is no one right way to do amateur radio, and that's one of its great strengths. There is so much to learn and do.

I began writing this article while the CQ WPX SSB contest was raging on the HF bands. I made 100 contacts, got bored and quit. Since I have a passion for contests, my disinterest may seem surprising. That is why I built and keep improving my "big gun" station. Most hams are impressed by what I've built when they come by to visit, although, truth be told, some think that mine is a pointless pursuit. They are correct, from their perspective; they have different interests and motivations.

Too much of a good thing can be bad for you. It leads to fatigue. No matter how much you love doing something, taking breaks from it can be very refreshing. The break can be a day or 20 years. There are many days that I won't even turn on the rig or monitor DX spots. I avoid the shack and do something completely different and unrelated to radio.

DXCC Challenge

When a break doesn't refresh your interest, it may be time to find another passion. This brings me to the subject of this article: pursuit of DX band slots. The idea is to work as many countries on as many bands as possible, and even for every mode. There is an award for this pursuit: the DXCC Challenge.

With 340 DXCC entities and 10 bands (160 to 6 meters), the award pinnacle is 3400. You can work them on SSB, CW or a diversity of digital modes, but you'll never work them all. With no end in sight, what exactly is the objective? It can be a lifelong project.

I have a friend who is closing in on his 2500 endorsement for the DXCC Challenge. He'll never approach those at the top of the DXCC Challenge list (over 3200), but he is passionate about getting to 2500.  He has resorted to FT8 to find DX stations in rare entities that are not active on the traditional modes. 6 meters is another option he's pursuing. He is making progress and I expect that he'll reach his goal this year. I wish him well in his quest.

After that? Quite a few have stretched the possibilities to surpass the 3000 level. How many? Hundreds! Do the arithmetic and you'll see just how difficult that is: it's just about impossible to do it on HF alone, even by dedicating decades to the pursuit. 6 meters is mandatory if you're serious about the pursuit. But it can be done. Is it worth it? I am in no position to say.

I am close to 2000 band slot confirmations on LOTW (Logbook of the World) for the DXCC Challenge award. Over my long ham career, I have hundreds more worked and confirmed on paper that I refuse to sift through. I've gotten this far without really caring about the DXCC challenge. I'll probably never apply for the award. It's interesting to track my progress, but that's all. I have even less interest in chasing grids on 6 meters. Again, it's interesting to monitor how I'm doing on the VUCC grid count. Many hams are as passionate about the VUCC award as others are for the DXCC Challenge.

The role of technology

Despite these sentiments of indifference, I do have the urge to work DXpeditions on every band they activate. I like chasing DX, so why not. Many who fish can enjoy themselves without catching any fish: drop the line into the water and soak up the sunshine. You can enjoy the chase whether or not you log the rare DX. Catch and release of fish is a little like working the DX but not confirming the contact. I'm like that.

At the other extreme are those for whom the award is all, and they will bend and break the rules of the competition to get it. Fake contacts, paid contacts, fake confirmations, excess power and more. You see it in DXing just like you see it in any competition. I won't say more on this aspect of award chasing other than to note that it exists and I don't let it poison my enjoyment of the chase. I am not competing with either the cheaters or the non-cheaters.

DXCC Challenge is to some extent a product of technology. Decades ago it would have been a Quixotic pursuit. Without the benefit of spotting networks, live streaming and real time updates, an inordinate amount of time would be needed to hunt down each DXpedition on every band slot. In many cases the propagation is so marginal the rare DX station wouldn't be able attract callers by CQing. Sometimes they will self spot to announce their presence. 

Even retirees have limited time to spend in front of the radio. Few want to spend that time slowly spinning the VFO knob across every band and at frequent intervals become the first to find the elusive DX. Sure, the pile ups can be intense when the DXpedition is spotted or an alert comes from their we site, but it eliminates the tedium of always searching.

And when you do find the rare DX by your own hard work and work them, what do you do next? In the old days you would call your friends and they could work the DX without fighting through a pile up. You can find descriptions of these techniques in the now very old but excellent book, The Complete DXer by W9KNI. DXing was not always a solo pursuit. Groups of friends would draw up a schedule of bands and times for each to monitor for that elusive and rare DX. When one of them found the DX the telephones and pagers started ringing.

With technology these small circles of friends have become far larger. It no longer matters who you know and nothing is asked of you in return. Technology gives everyone a chance for acquiring a multitude of new band slots. The competitive playing field is more level than ever. The old ways are obsolete. DX clusters are globally networked and skimmers often find CW stations before humans do.

Digital levels the competitive field further. Those with small stations can get through the pile up far better than on CW or SSB. Digital decoding algorithms don't care if you're weak or strong, and will pull you out even when you're buried beneath stronger stations. I know many little pistols thrilled by how much rare DX they can work on FT8. With their small stations they often work DXpeditions on FT8 before I do it on CW.

Technology enables everyone -- big station or small, skilled operator or merely competent -- to climb high on the DXCC Challenge ladder. Not everyone would agree that this is a good thing: it's called a challenge for a reason.

What's the point?

There are so many possible band slots that it can lead to fatigue. Just how hard do I want to chase CY0S (a recent example) on the high bands, where working them from a short distance is not easy. I did try on 6 meters, just because 6 meter DX is a special passion of mine. They did show up on CW but quickly turned to digital since it put more stations in the log. First it was FT8 and then MSK144. 

It's possible that they logged me on MSK144, but without a definite acknowledgement of my RR73 message it's impossible to say. It is profoundly unsatisfying to wait for their log upload to learn the answer. This is a question that has to be asked far less often on the traditional modes.

(Credit: ClubLog; screenshot taken March 29, 2023)

[I can now answer my own question. As of March 30 I am indeed in their log for the MSK144 contact. However, my statements above stand. I haven't bothered to update the screenshot.]

I could try again. I won't, nor will I turn on the amp and try to break through the pile up to work them on the high HF bands. Perhaps I should write this in the past tense since CY0S is about to go QRT as this article is being published on the blog. Eventually there will be other DXpeditions to Sable Island when, perhaps, I'll feel more motivated to try to fill those band slots.

Running the bands when every DXpedition pops up can become a chore rather than a pleasure. It isn't a great challenge most of the time when all I have to do is watch for a spot to appear and apply maximum power to my large antennas. Often I create a handicap for myself, to artificially boost the challenge, by leaving the amp turned off or use whatever antenna is more or less pointed in the right direction. I enjoy practicing my pile up skills. I practice related skills by occasionally operating QRP in contests.

For me the most important challenge was in designing and building this station, and then to practice and hone my operating skills. Piling up the DXCC band slots is one way to profit from my labour. I don't do it too aggressively since, for me, the fun soon fades. My band slot enthusiasm is mostly reserved for 6 and 160 meters, finding and working rare DX on difficult paths, or by skillfully threading large pile ups. The DX doesn't necessarily have to be rare. Nor do I get too disappointed when I fail to work them. There's always next time.

Meaning

The meaning of DXing, as it is with life, is up to you. It is not handed down from on high. I love chasing DX but it does not define me. I'll do a lot to bag the DX and, yes, on every band slot I can, but only up to a point. I have no interest in spending the time and effort to reach 3000 band slots for the DXCC Challenge. I don't chase any DXCC certificate. I enjoy watching the numbers increase, and that's good enough for me.

Radiosport will only grow in our hobby. Extreme DXing is one part of that, and contests are another. Participation in both is growing. Hams find meaning and enjoyment from those activities. Despite my disinterest in chasing every band slot, I would never say that others are wrong to do so. Meaning is a personal choice and I don't begrudge them their passions.

What I really need right now is spring weather and not the blustery cold and wet we've been dealing with. That would be especially meaningful. I can then spend more time outdoors working on antennas and less time writing philosophical tracts!

Automating VA6AM 6-band BPF

The VA6AM switchable 6-band low power BPF (band pass filter) product does not exist. Or at least, not yet. I believe that mine are still the only two in existence. Pavel has little time for this product to have a higher priority. I was fortunate that he undertook completion and testing of the relay boards and the 6 BPF modules at my request. I've used these filters in many SO2R contest operations and I'm very satisfied with their performance. 

Eventually (as I've promised a few times) I intend to say more about these filters on the blog. This will have to do for now. Pavel had not completed the control board for the filters and I needed one to integrate with my station automation. 

I purchased 8-position rotary switches to enable manual band selection as a temporary measure when the units were built. Rather than wait any longer I decided to proceed to integrate the filters into my station automation project with a home brew solution. 

The BPF are now automatically selected when changing bands. Manual operation remains an option when automatic switching is disabled or not functioning. There is a bypass feature for when a non-contest band is selected or it is manually turned off. I leave the BPF wired into the station at all times since their presence, in bypass mode, has no measurable effect.

The 8-positions of the rotary switch are (clockwise): Automatic (no written label); Out (off or bypass); 160; 80; 40; 20; 15; 10. Until the recent upgrade the Automatic position was equivalent to Out. The front panel control is ugly, with temporary labels and no LED indicators. Perhaps I'll add them when I get the urge. It isn't difficult but it also isn't urgent or necessary.

Manual operation is quite simple. The wiper of the switch is connected to the +12 VDC power socket on the rear panel. The relays for each band on the two relay boards for are connected to their respective positions on the rotary switch. The bypass relay is powered by diodes that leech the power from all the band relays. There are 4 relays energized when a BPF is selected. The total current draw is 120 ma. Two indicator LEDs would add another 40 ma.

The Automatic position on the rotary switch has more complex wiring. It is connected to the band selector DE9 connector on the rear panel. Of the other 8 conductors, one is power (+12 VDC), one is ground (as is the cable shield) and the other 6 are band selectors that carry +12 VDC when the band is selected. These are wired to the rotary switch in tandem with the wires to the relay boards, as described above. The straight-through DE9 shielded cable connects to the BPF driver board in the automation system.

Yes, the wiring of the rotary switch is a mess! Had I planned everything in advance it would have a connector board. The LEDs, when I get around to it, will go in a row on the front panel or positioned around the rotary switch. I'm not sure which would look better. The automatic mode LED will be a different colour than the band LEDs.

The Cat5 cable runs under the BPF boards and doesn't affect their behaviour. On the enclosure above the cable runs under one of the relay boards. I should have done them both this way but, as I said, there is no problem having it under the filters. Toroids isolate themselves very well and the more sensitive solenoid coils in the 10 meter BPF (above left) are sufficiently shielded by the PCB ground plane.

For automatic operation the power socket is redundant; power comes via the 9-conductor cable to the automation system. The BPF operates as before for manual operation. In automatic operation, the +12 VDC from the Automatic position on the rotary switch powers the switching electronics in the automation system. This is shown below (connections from the band lines to the rotary switch are not drawn).

In manual operation when the switching electronics are not powered, the GPIO pins driving the 6 band lines cannot power the BPF relays. There should never be conflicting control of the BPF relays from both manual selection and the automation system. Switching two BPF inline would be bad. However, there is an unfortunate though non-destructive interaction that I'll discuss towards the end of the article.

The software does not have to be aware of whether the BPF are operated manually or automatically. The operator decides whether to operate manually or automatically by turning the rotary switch. Software does not trigger any GPIO for bands other than the 6 HF contest bands. When only one radio is in use (SO1R) the other radio's GPIO are idle. There is no check for whether the two sets of BPF are on the same band. Conflicts must be resolved by the operator(s), software or by antenna port lockout.

There are other ways to accomplish both manual and automatic switching of the BPF than what I've built. You may be able to think of one or two. I did it this way for simplicity of hardware and software, and intuitive behaviour for the operator. At least it's intuitive to me, and I'm the one who matters most at this station! 

One alternative is to have a band decoder for Yaesu/Elecraft or Icom coding within the BPF. The decoder must manually or automatically detect the coding scheme for different manufacturers. If the band data from the transceiver is needed for other automation task such as for an amplifier, they must be wired in parallel. I have done away with hardware signalling by extracting it from N1MM's RadioInfo UDP messages. The Arduino thereby knows the band and can send +12 VDC to the BPF on each band's dedicated line. 

The BPF requires no control board when used with my home brew system automation. There is just a straight-through DE9-DE9 male shielded cable. There are commercial BPF that support a similar per-band DE9 pin, so my interface is not unusual. However, the connector pin out is likely to be different from any existing product.

Driver circuit

Two types of driver circuit were considered: electronic and electro-mechanical. The first is compact and silent, and the second is noisier and larger. I have opted to use relays for all control lines exiting the house since they are better at handling lightning surges and precipitation static. I ground the control lines via the SPDT relays for high side switching. That cannot be done for low side switching. All my home brew antenna switching systems use high side switching. The 2×8 Hamplus antenna switch is the only device in my station using low side switching.

Since the BPF and the control lines are inside the shack and not directly susceptible to weather events, I decided to use electronic switching. I have a spare Arduino-compatible 16-relay module that was my fallback in case the electronic solution became too difficult. The BPF require high side switching.

I learned something new about PNP transistors while bread boarding alternative driver circuits. A pull up resistor is needed to quench the switch and turn it off. The same appears to be true of the PNP Darlington transistors I am using. It isn't enough to set the GPIO pin High since the GPIO's 5 volts is lower than the 12 volts being switched. Since I am using reverse logic (GPIO Low is On), I naively thought I could drive the Darlington transistors directly from the GPIO with just a base resistor. A pull up resistor would be disastrous in this circuit since it would place +12 VDC on the GPIO pin and fry the microprocessor. 

I resorted to the more common 2-device solution. An NPN transistor drives the PNP Darlington. No pull up resistor is needed for proper operation and the Arduino GPIO pin is protected from the higher voltage. This may be an odd implementation of a complementary Darlington transistor but I had the parts on hand and it works. The doubled parts count, from 2 to 4, requires more PCB area. There is no cost penalty since the parts are absurdly cheap.

I bread boarded two drivers to test them before proceeding to construction. Testing a circuit is highly recommended before soldering 12 of them on a PCB. LEDs are a convenient substitute for relays since no extra test equipment is required and they glow. Keep in mind that an LED is inadequate for testing applications where the actual load is high current (an LED only consumes about 20 ma). The driver circuit schematic is shown further below.

There are 4 Omron SPDT relays energized when a BPF is selected, along with two optional LEDs. The total current is roughly 200 ma. For a PNP high side switch the voltage drop across the Darlington transistor is approximately 0.7 volts. Since P = EI, the power dissipation is 0.15 watt. Heat sink are not required on the Darlington transistors. The voltage drop itself does not affect the BPF relays since the nominal 12 VDC coils operate over a wide range.

The PCB is small and crowded with 12 drivers, connectors and wiring. A larger proto board would have been easier to work on. I chose a board with two holes per pad rather than one with long connected vertical and horizontal rows. Layout has to be sparse for the latter and there would be much wasted space in this application. Those proto boards worked well for my Beverage antenna reversing electronics since there were fewer components to mount. A custom PCB would have been easier to work on by eliminating all the wiring, but at a significant cost for just one board. 

The main cost of this board was the endless frustration of fitting and soldering small components and wires with magnifying glasses. I took care to avoid cold solder joints, bridging pads and overheating wire insulation and transistors. I was lucky to have only one cold solder joint and another where there was a high resistance leakage between stages. Aggressive cleaning of flux and spreading wires apart fixed the latter.

The cable harnesses for connection to the Arduino and BPF were another source of frustration due to their small size. A couple of bad crimps were easily repaired. The Dupont connectors with 0.1" spacing fit the board nicely. I went with all male connectors for their low profile and ease of cutting from the long chains they're sold as. The low profile eases component and wire mounting. The 9-pin connectors to the BPF are ideally female so that power pins are not exposed.

In retrospect, the layout could have been improved. I also didn't need the above board power rails. To avoid crossing wires, the 3.3 kΩ resistors are mounted below the board. In the end, what matters is that it works, and it's okay if it's ugly since it'll be out of sight.

You may have noticed the lack of bypass capacitors to prevent RFI. The cables are short and shielded, and the control lines are bypassed on the BPF relays boards. There has been no trouble with RFI. Capacitors will be added should RFI arise in the future.

The driver board was connected to one of the BPF units after testing each circuit with LEDs. That's when I discovered and corrected the problems mentioned above. I accidentally scrunched a couple of the bottom resistors when I was too aggressive pressing on the 9-pin connector. I was lucky not to do more damage when I levered up the scrunched resistors with a small screwdriver. 

Testing proceeded well after dealing with the aforementioned difficulties. But there was one problem I discovered that is not easy to resolve. It's an odd case that is very unlikely to occur in actual operation so I am not going to deal with it, at least not now. It occurs when the BPF is operated manually by the operator while the driver board is connected and operational.

Let's say you turn the rotary switch to 15 meters to manually select the BPF. The relays function as intended and the 15 meter BPF is placed in line. However, if the rig is on another band (10 meters), the BPF relays for that band are also energized. That connects two different BPF in parallel, and that's bad. 

The reason for the misbehaviour is inherent in my design of the driver board. Although there is no +12 VDC directed back to the driver board from the BPF via the Automatic rotary switch when a band is manually selected, it is present at the driver board via the 15 meter control line. It is therefore present at all 6 Darlington transistors. The NPN transistor for 10 meters turns on its Darlington and the 10 meter relays are energized.

This was an oversight in my design. Wiring the control lines for automatic in tandem with the manual controls for each band selection is responsible. There are a few ways to correct the problem but, as I said, this is not likely to every happen in real life. There is no reason to manually select 15 meters when the automation system is working and tracking the transceiver to 10 meters. The glitch can stay.

I mounted the driver board to the rear of the open frame automation system, connected the several cable harnesses, glued rubber feet to the bottom and re-installed it in the station.

Was it worth it?

With this project done, the shack hardware for my station automation is substantially complete. That is one of the objectives I set for 2023. Of course I'll continue to expand and improve the software and extend the hardware for new antenna projects. But that only involves connecting or moving wires and not hardware changes.

Use of the automation BPF band switching in a contest will have to wait. Although I set myself a deadline of CQ WPX SSB this weekend, there will not be a multi-op or SO2R operation that requires BPF. There will be other contest opportunities in the not too distant future to give the BPF switching a full workout.

Although it's done and working and ready to go, there is the question of whether this project was worthwhile. It would have been far simpler and easier to use another Arduino compatible board of 16 relays, connect it to the GPIO and stack it on top of the other 3 relay boards. While I do not regret the effort and experience of building these electronic switches, and I like that they operate silently, it was a poor investment of my time. In retrospect I would have gone with the relay board. I have one in stock, as a spare, and I could have automated the BPF in a fraction of the time.

Home brewing is fun and educational, and I had the time since it was winter and (being retired) I had time for indoor projects. Now that spring has sprung and the weather is warming my thoughts are turning to the great outdoors. It won't be long before I dig into my growing list of tower and antenna jobs.