High Power SO2R Novice

I am not very good at SO2R contesting. It takes a lot of skill and practice, and I have little of each. I am working at improvement, but slowly. The IARU contest last weekend was particularly challenging for me since I was not at my best (bad year for allergies). It was my first SO2R experience with high power. My band pass filters are built and working and the two amps are wired up and ready to go. 

I've come a long way since I first tried SO2R. The filters were an interesting project that will in the future (but not the near future) be a topic for the blog. They are prototypes, built from kits, that the designer plans to develop into a product.

Since everything in my SO2R setup is manually switched, all the equipment has to be on the operating desk where I can access the controls. The desk is becoming very crowded (and my photography skills have not improved).

When I change bands on one of the two operating positions the actions I must perform are:

• Change the band on the rig
• Switch the band pass filter band
  
• Switch the antenna
  
• Switch the amplifier band
  
• Tune the amplifier

Over time my intention is to make all but the first automatic. That will take a lot of work and, yes, money. Some are not so difficult (filters follow the rig or software band data) while others require home brewing (antenna selection) and the purchase of auto-tune broadband amplifiers.

The following notes describe my SO2R experience with high power in the IARU contest. There are no great revelations. I document these items to help me decide what work to do on the station and which operating skills to improve. Other contesters might benefit from these notes as well.

The attraction of power

Big signals attract big crowds. This is great in a contest, if you deal with the pile-ups and weak callers. It takes skill and talent to make the most of it, and even more to do it SO2R. Having your concentration and focus rapidly alternating rapidly increases the challenge. With two radios the challenge is more than doubled. The progression is not linear. With power you run (and must run) more frequently and that imposes a discipline that is difficult to perform well without years of experience and dedicated practice.

I admire those who can reliably isolate one caller among many. It is more difficult when (on CW) they have almost identical audio tones, stations call out of turn, all amidst the QRM of a popular contest. Mortals like me often resort to sending partial calls (hoping the rest standby) and narrow filters. When the two QSOs slip out of sync (it's inevitable and frequent) you end up having to copy on both receivers at the same time. It is difficult but it can be done.

Weak callers are a different and in many respects a more difficult problem. Pulling out a weak signal may require temporary adjustment of receive audio level, RIT and selection of antenna or receive antenna (low bands). Many of those weak stations aren't QRP but stations in a direction not favoured by your antenna. Remember, you have a big signal so hams everywhere will hear and call you, not just those you're pointing at.

The solution is practice, practice and more practice. At the moment I am struggling to deal with the many callers a big signal attracts. It can be a lot of fun but, oh, what a mess!

Signal quality

SO2R is one of those rare occasions when you have to eat your own dog food. Does your transmitter have key clicks, phase noise, excess harmonics, IMD, hum and other signal quality problems? You have to put up with it on the other radio. The majority of hams never really know how their signal sounds to others on the band, and most hams are too polite to say. The transceiver monitor feature is of no use to assess RF signal quality attributes that impact others on the band.

For low power BPF the transmitter harmonics are strongly attenuated. This is not the case for amplifier generated harmonics. No amplifier is perfectly linear so there will be harmonics; the BPF on the other radio does not filter in-band harmonics. You remove harmonics with band-switched notch filters (coax stubs) or more expensive high power BPF.

This is more frequently a CW problem since the harmonic relationship of the HF bands permits more opportunity to encounter harmonics your own harmonics. One avoidance technique is to operate near the lower end of the higher band and the higher end of the lower band. Compare the potential interference of the combinations 7020 and 14040 versus 7040 and 14020.

Harmonics are broader than the fundamental signal, being two and three times broader at the second and third harmonics, respectively. The harmonics of a dirty signal can be brutal. These include key clicks, phase noise and IMD. The second 40 meter harmonic of my FTdx5000 can wipe out 15 to 20 kHz of usable spectrum on 20 meters. This is with the latest firmware and options set to minimize key clicks. High power worsens the problem by 10 db, which is a lot.

I am increasingly disillusioned with the quality of Yaesu equipment. Signal quality flaws have been baked into their designs for decades. When the shack equipment is updated the Yaesu transceivers will be replaced.

Managing the amplifiers

Both amplifiers -- Drake L7 and Acom A1500 -- are tube amplifiers that must be manually tuned. Correct tuning of the latter is more difficult due to the power tetrode design. The grounded grid triode design of the L7 is more forgiving.

For every band change, large frequency shift or antenna selection the load and plate controls require adjustment. A quick antenna swap to work a multiplier is easier with the L7 since you can get by with a mistuning for a QSO or two. The A1500 is less forgiving. For that reason I strove to have the left radio with the A1500 always running. In the long run it saved time.

One particularly annoying aspect of tuning the amps is the transmitter power setting. Not all transceivers have a front panel control for power: the FTdx5000 does and the FT950 does not. For the latter it's a menu item. Before the contest I set the menu to the entry for power for rapid access. Rigs with small physical size are more likely to hide this item in a menu to save panel space. The power level must be higher when using BPF to compensate for filter losses -- in my case, from -0.22 to -0.55 db.

Eventually I hope to have all low SWR antennas and broadband amps, perhaps with an ATU. When that happens there will be no need to repeatedly fine tune the amps. Band and frequency changes would require no operator action in most circumstances. Not always, of course, since not all antennas are so perfect and weather can play havoc with antenna impedances. There will always be a need for manual tuning or reprogramming of the ATU

Time spent tuning is time not spent working stations. It is also a task that accelerates operator fatigue. SO2R is particularly difficult since you are working stations on the other radio while tuning the amp. I had to be quick or be interrupted by the QSO in progress.

Hot as heck

The typical efficiency of a linear amplifier running in class AB is no better than 60%. For a power output of 1000 watts there will be 700 watts or more of heat dissipation, plus that of the filaments (tube amps) and heat due to the inefficiencies in the power supply. The same is true of the transceivers. Luckily the duty cycle is not 100%. To be more precise, it isn't 100% on each radio but close to 100% overall with SO2R.

Since the objective is to transmit at all times, by alternating the two radios there is always a transmission occurring. With CW or SSB the effective duty cycle is about 50%. Put it all together and the continuous heat dissipation in a high power SO2R station is around 600 watts. It will be different in each country for those operating at the legal limit (e.g. 1500 watts in the US).

Our summers are short, hot and humid, and the peak is July. A mid-July contest guarantees that the shack will be uncomfortably warm. The air conditioner is not a perfect solution since the thermostat is not in the shack. Dress accordingly and have liquid refreshment within reach. In our cold winters the amps keep the shack warm and cozy.

Software reliance

Computer hardware and software are integral components of the modern contest station. You can resort to the 3 P's in an emergency -- pen, paper and paddles -- at the expense of time, rate and a horrible mess to deal with after the contest. Suffice it to say that the machinery should be kept in good working order.

I had computer and software issues for the first hours of the contest. SO2R was very difficult. From diagnosing the problem I discovered that Windows 10 was waging a forever war against a privacy protection app running in the background. The 2 keyboard feature of N1MM Logger+ is very sensitive to latency and I had severed latency. Key presses frequently went to the wrong radio's window. Once I corrected the problem the software preformed as it should. Microsoft won this round.

There is more to be done to reduce the severity or recurrence of problems like this. The PC is dedicated to the radios and I typically have no other apps running during contests. 

I have modest RFI issues with the PC which are exacerbated by high power. This is primarily a 40 meter problem since that is the only HF contest band for which I have an antenna nearby. The RFI has not yet caused a computer or interface failure. More ferrite chokes on cables must be installed to reduce the risk. I've been lucky so far.

Physical condition

SO2R is intense. It demands a lot from your mind and your body. You must remain alert for long periods and have the physical endurance to manage the equipment, listen, log and make frequent choices about bands and directions to target. With 2 keyboards the physical demand is greater due to swivelling back and forth between radios, and some awkwardness using the paddles and mouse which may be difficult to reach and use amid the desk clutter.

High power is more demanding because the rate is higher. QRP SO2R can be quite relaxed since there is often just one QSO happening at a time. Low power boosts the rate enough that it is almost never relaxing. High power SO2R is frenetic.

As we age our concentration and physical endurance deteriorate. On the positive side, SO2R helps fight the decline: use it or lose it. Although I am fit for my age it still becomes a grind as the hours accumulate. Although I practice and do the best that I can, I will never be an great SO2R operator. Oh, to be young again! Actually, I doubt that youth would help me. The inherent talent is weak in me. We can't be good at everything, so we do the best with what nature gifted us.

Next steps

For the next while my focus will be on antennas and not station automation. I'll live with the shortcomings of my SO2R setup until then. I could move faster to get everything completed sooner but, hey, it's a hobby.