Eking Out the Decibels on 160 Meters

160 meters has a lot in common with VHF and UHF. Propagation effects are subtle and often there is no skip zone. This means that the farther the station, the weaker the received signal.

From day to day the signal strength of the same station varies a modest amount, and not to extremes we see with HF ionospheric propagation. If you can't work a station today there's a very good chance you can't work them tomorrow, or if you do it'll be marginal. Every decibel counts, even if you are patient and willing to wait for enhanced propagation. 

On HF,  due to the wide hourly, daily and monthly signal strength variation, you need only wait a little while for propagation to come your way. When it's good, QRP can work the world. When it's bad, a kilowatt and stacked yagis are not enough. Power and antenna gain certainly matter on HF for more reliable communication (and contest scores!), but for the casual operator it is usually acceptable to work what they can with the station they have.

Which brings me to the frustration of the CQ 160 contest last weekend. Overall the conditions were atrocious. It is in these conditions that every decibel counts when it comes to being heard. The small differences among stations -- antenna, power level -- made a large difference in the outcome.

When signals are close to the noise level even 1 decibel can make a large difference in whether a QSO can take place. When conditions are good that slight edge is nearly irrelevant: S7 and S7 + 1 db are indistinguishable.

Under the poor conditions prevailing during the contest only the very best stations and the most persistent operators did well when it came to working stations far away, whether it was across the ocean or across the continent. Success also requires good ears and high RDF receive antennas, however in this article I want to focus on the strength of the transmitted signal; that is, being heard far away.

Barring a change of QTH, there are several strategies available on 160 meters to improve transmit signal strength:

• Improve antenna effectiveness
• Improve antenna efficiency
• Increase antenna gain
• Increase power
• Wait for the other station's reception to improve

Antenna effectiveness

An effective antenna on 160 meters is difficult for the majority of hams. My first effective antenna went up in 2017 and I've been a ham for almost half a century. Many never have the opportunity. The wavelength is so long that it is difficult to have an antenna that is big enough or high enough.

An effective antenna is one that is compatible with the propagation mode and direction. With limited exceptions the most effective antenna on top band is a vertical. A horizontally polarized antenna, such as an inverted vee, is so low to the ground with respect to wavelength that it is very poor at low elevation angles, and like a vertical it is vulnerable to ground loss.

The 160 meter antennas of most hams are only moderately effective. For casual DXing it may be acceptable to wait, but in a contest waiting isn't an option. Unable to wait or raise a more effective antenna, the contester must focus on other strategies.

Antenna efficiency

An efficient antenna is one that radiates most of the applied power rather than dissipating it in the antenna or the local environment. Short antennas require loading or matching networks that can turn a large portion of the power into heat. Low horizontal antennas and vertical antennas lose a lot of power in the environment surrounding the antenna, most notably the ground. The wavelength is long so the antenna near field is large, with ample opportunity for loss.

A half size antenna (e.g. 20 meter high vertical) has a radiation resistance of several ohms. As a consequence, the ESR (equivalent series resistance) loss in loads, matching networks and ground can easily surpass 50%  (3 db) of the applied power. It is often far worse. For example, in my on-air tests of my short vertical (base matching of an 80 meter vertical) it is at least -6 db compared to my full size vertical.

For greatest efficiency the loading elements (coils, capacitance hats) should be far from the feed point and have the maximum Q (minimum ESR) we can attain. Inverted L and T antennas are examples of short verticals with large capacitance hats.

Verticals need a ground with the lowest possible ESR. This requires many on-ground radials or a smaller number of elevated radials. The elevation of the latter should be at least 10 meters or you'll still need lots of radials. As the vertical gets shorter, and the radiation resistance drops, the radial system becomes ever more critical. Unfortunately, an extensive radial system for a short vertical is often impractical, usually for the same reasons the vertical is short: not enough land.

For the same radial system, an antenna with gain will be less efficient because the gain is almost always accompanied by a lower radiation resistance. Efficiency on top band is never easy.

Antenna gain

Gain requires more than one antenna element. For those struggling to raise one antenna that is both effective and efficient, imagine how much more difficult it is to raise 2, 3 or 4 elements. It may be more than 2, 3 or 4 times more difficult. There is the increased land area, increased material quantity, pattern-destroying interactions with towers and buildings, and a switchable and complex network to phase, steer and match the array. 

The radial system for each element must be more extensive than for a one element antenna due to the lower radiation resistance. Otherwise the realizable gain will be reduced, calling into question the additional investment.

Should you decide to proceed, be prepared to achieve a maximum of 4 to 5 db. Getting beyond that will require an effort that only a handful have done. For example, a full size 4-square with 10,000 meters of radial wire. The simplest 2-element vertical array will net you no better than 3 db gain.

On top band, antenna gain does not come easily. It requires passion, time, money and land. Acres of land. The poorer the soil the more that must be invested in the radial system.

Power

Changes in the shack are always easier than changes outside. Wire an outlet, plug together a few more cables then browse the web site of your favourite ham retailer and click "Buy". A few days later you will see a 10 db boost to your transmit signal, on 160 meters and all the HF bands. 

This may not the cheapest path to a big signal but it is a dependable one. Many hams are old enough to have a little money saved up, so the purchase is within reach of most. You can't buy a 160 meter antenna that will get you anywhere close to the same improvement. Antennas must be built, while power can be bought.

You are not necessarily limited to 10 db. Starting with 100 watts that will take you to 1000 watts, and in many countries you can legally go beyond this by 2 db or so. I am sure you know hams who have not stopped there. I have been in shacks where a 4CX2500 is humming, and sometimes two of them. 

Many years ago I had an amp with a 4CX1500B and a stiff power supply that easily exceeded our legal limit. I rarely used it that way since that was back when home electronics were more susceptible to EMI. I chose to minimize friction with the neighbours. In any case, I didn't have an effective 160 meter antenna. I rarely operated on top band.

Unlike antenna improvements, boosting power is not reciprocal. Unless you invest in high RDF (directive) receive antennas the improvement may be wasted. We have all experienced the alligators with big signals and no ears. They're solid copy but respond to few. CQ machines only benefit the local electrical utility. But they do keep the shack warm through those long winter nights.

Other station's reception

Waiting for better propagation is always an option. Unfortunately, like Godot, it may never arrive. Hope is not a strategy. We need a more predictable outcome, whether it is during the heat of a contest or for chasing rare DX.

One semi-reliable method is to watch the sunrise terminator as it sweeps across the target. For a brief time, from a few minutes to half an hour, their noise level drops and the path remains open. The key on our end is the former: their receive SNR increases at their sunrise as atmospheric noise from the other direction, towards daylight, is attenuated by the re-ionization of the D layer.

I did not stay up until European sunrise either day of the contest. Those who did were able to work stations they could not work earlier. Of course I knew this might happen but I didn't think it worthwhile to stay up into the wee hours to win multipliers in a contest I was not competing in. 

A few decibels on the other end of the path can do wonders for your contest score or to put a new country into your top band log. Those decibels are a gift because you cannot buy them. When it happens you need to be there to receive the gift.

Summing up

The quickest route to being heard is more power. Going from 100 watts to 1000 watts is 10 db, and it is impractical for the majority to get anywhere near this from antenna improvements on 160 meters. If you're already using a small 800 watt amplifier, going to 1000 watts is 1 db, and even that small increase can be difficult to get from antenna work.

During the CQ 160 contest, with my Beverage receive antennas I heard far more DX stations than heard me. My enthusiasm to continue operating quickly waned since my top objective was to use the contest to work DX. A full size vertical with 8 radials didn't give me the edge I needed. 

With lots of effort I can squeeze a few more decibels from my 160 meter antenna. Some of that work I will certainly do, however I won't go to an extreme effort. I can already put plenty of contacts and multipliers in my contest log, and I am competitive in the pile ups. A better amplifier will suit me better.

Although I love antennas and antenna work this is one of those places where power rules. I am not saying that antenna work is pointless, just that the fastest, biggest and often the cheapest solution is more power. To be a top band big gun you must do both. There are no shortcuts.

In the end, you invest the time and money you want. After that, for most of us, you learn to appreciate what you have.