Everyone Needs a Receive Antenna on 160

With the CQ 160 meter contest coming up this weekend I thought it worth a brief article on the importance of receive antennas. That is, antennas with directivity that improve reception (RDF - receive directivity factor) in the favoured direction(s). Top band big guns have them, and must have them, but too many others do not. 

Allow me to give you a perspective on receive antennas that you may not be familiar with, especially if you are a little pistol on 160 meters. I know operators that venture onto top band during contests and fail to do as well as they might. It's not because of a poor antenna -- an effective and efficient transmit antenna on 160 meters is very difficult for most hams.

This is the scenario. I have a very effective omni-directional vertical as my transmit antenna. I also have several long, reversible Beverage receive antennas. When I hear a weak station and call them, they often don't hear me. Many of those stations are little pistols with small antennas and no more than 100 watts. They ought to be able to hear my big signal since an inefficient antenna is no detriment to reception on top band -- both band noise and signals are similarly attenuated on receive, and therefore do not affect the SNR (signal to noise ratio).

The problem is one of reception reciprocity, or rather its lack. If the other station had a means to improve RDF, we would make the contact. It would only require a few db since in many cases they hear something but not enough to copy me. We both miss adding another contact to our logs.

I can't easily remedy the issue from my end. I run the legal limit and a transmit antenna with directional gain may never happen. A gain antenna is not a perfect solution since 2 or 3 db will put me in the logs of more stations, yet there would then be another layer underneath that I will hear and which won't copy me. Other than running more power, beyond the legal limit -- which I won't do, I like to play and win by the rules -- I'm stymied. .

If you are among the multitude of small top band stations, do not fall into the trap of thinking that a receive antenna is of no benefit. Other than those with exceptionally bad local man-made QRN, even a little receive directivity will help. The hams I've spoken to about it believe that there is no point to a receive antenna since they are pessimistic about their ability to be heard.

Don't assume stations you could only hear with a receive antenna won't hear you!

You might be surprised by how effective a receive antenna can be, and many stations have them. They'll hear you. Even if they're weak, they could be a little pistol as well assisted by a peak in the highly variable propagation. I've worked a surprising amount of DX with QRP on 160 during contests. There are pretty good receive antennas that can fit into a small space.

Always call the weak stations, no matter your antenna or power. They will often surprise you. You can't know in advance whether they have good receive antennas.

Be optimistic and make the effort to hear better. It might only take a small loop with a sharp null to drop a particularly bad noise source by 10 or 20 db to hear many more stations. You only need one in this particular situation. If the problem is noise from all over, a switchable multi-direction receive antenna can boost SNR by 6 db or more in each of its directions. 

Examples of very small antennas include the WD8DSB portable loop (March 2021 QST) or a fixed/rotatable loop with bidirectional nulls. Examples of larger but still modest antennas include the K9AY array, short Beverages or BOG (Beverage on ground). If a short Beverage is still too long, other options usually fit nicely into most suburban backyards.

Once you have a directional receive antenna with multiple available directions you will have a new challenge: constant switching, in my case by endless clicking of the mouse. 

The need arises because you almost certainly have an omni-directional transmit antenna. On 20 meters and up this is rarely an issue since a single directional antenna (e.g. yagi) is used for both transmit and receive. If you call me and I don't reply, call again. It may be because I missed you while listening in the wrong direction or hadn't yet determined the correct direction.

Unless the 160 meter opening is decidedly in a single direction (fairly common at sunrise and sunset) you will find yourself having to check multiple directions for stations. You have to do it whether running or hunting, though more frequently for the former case. It's worth the effort to add those precious contacts and multipliers. 

Speaking of the terminator, you will find that your omni-directional transmit antenna has an improved apparent RDF at sunrise and sunset. The reason is that one half of the "sky" is lit. The ionosphere's D-layer ionizes within minutes of sunrise (and a little longer to de-ionize after sunset) so that the hemisphere towards the sun goes quiet. That's a gift worth of 3 db or more of RDF towards the darkness, and that's where the signals are found. Little pistols without a receive antenna have this narrow window twice a day. If there is no serious competition for the DX station when the terminator crosses your QTH, you can copy them better and, hopefully, they will hear you. The transition doesn't last long so be quick!

If you are sufficiently motivated by your experience with a small receive antenna, there are better ones you can build. You'll just need the space for them: 1 acre or more for vertical arrays and perhaps more for Beverages. Vertical arrays perform better while Beverages are simple and highly effective. 

I have toyed with the idea of putting up a vertical array but not for the additional 2 or 3 db of RDF. My concern is maintenance. Those long wires through the bush take a lot of abuse from trees, animals and lightning. 

If you don't have a directional receive antenna and you are intrigued, you probably can't put one up in time for the CQ 160 contest this weekend. But you can do something in time for the next contest, or just for DXing. If you haven't yet taken the plunge I hope this article has given you food for thought.