What to do when the bands suck?
Solar cycle #25 has reached its peak and is on the decline again. We may still have a few years of good propagation left but I am planning ahead. During the last solar minimum I adapted by … forgive me … increasing my transmit power. This time around I hope to keep working QRP, but increase my effective radiated power through bigger, more efficient antennas.
The peak of cycle 25 was actually quite a disappointment. The Sun became hyper-active spewing a few too many Coronal Mass Ejections, flares and high energy particles our way. Hopefully, now that the peak has passed, we might even get some less unpredictable propagation before we hit solar minimum.
As solar activity declines the higher bands seem to be open less often, so my personal focus is on 20m, 30m and 40m. Those bands are open throughout the solar cycle – except during solar storms of course. At least once per week I venture onto 80m for a CW rag chew with friends, but that is at the home QTH. When operating out in the woods 20m, 30m and 40m are my goto bands.
The sign should also warn that bears don’t react well to posing for “selfies”
On the subject of “out in the woods” (my happy place), our local black bear population has awoken from its winter slumber and has been seen roaming in people places in my local town.
Bears are not usually a problem, they avoid human contact, but in the spring they are hungry and some of them associate people with food. Female bears with cubs can be very protective of their young which makes them potentially dangerous.
Antenna solutions for challenging conditions
One simple rule should be all that is necessary for getting a signal to propagate when the ionosphere is in combat with an angry Sun – or even when the Sun is dormant. Wire in the air = signal in the air. That is when it is probably a good idea to leave those very short, inductively loaded whips at home and start buying reels of wire and poles.
When I look back at what has worked in the past, the picture becomes very clear. Some of my small collection of QRP radios support only 20m, 30m and 40m. The 20m and 30m bands usually favor longer distance contacts, while 40m is better at shorter range. Out of these three bands I use 20m the most and, during the bottom of the solar cycle, 40m is my most used band. I don’t get on 30m very often; it is a WARC band and some operators dislike “contest-like” activity such as POTA on the WARC bands. No sense creating friction.
Best option for 20m?
This may be a bit of generalization, but a half-wave antenna launches more signal in the air than a quarter-wave. All half-wave antennas are not created equal. For example the very popular End-Fed Half-Wave requires a very carefully engineered matching device. Improperly engineered, one-size-fits-all, high ratio transformers often have very low efficiency.
A 5/8 wave vertical antenna may be even better in some circumstances – for example when the base of the antenna and all the radials are raised above ground. But 5/8 of a wavelength is a bit of a tall order – on 20m that’s 41 feet of antenna waving in the wind. Raise it above ground and you may have to attach a flashing red light at the top.
There is an even better solution. How about a 20m wire antenna that is low to the ground, is slightly directional and offers over 3dBi gain? Ham Radio Outside the Box explored this antenna three years ago; it is called the VP2E. Although VP2E sounds like a callsign (and it actually is a valid callsign) it is an abbreviation for Vertically Polarized 2-Element. It requires no tuner – and the VP2E is one full wavelength long.
VP2E antenna
I had great success with my VP2E before I stopped using it. It fell out of favor because of just one thing. Proponents of the VP2E claim that no baluns, ununs or feedline chokes are required. Perhaps, in theory, if the currents on either side of the feedpoint are balanced that could be true. In practise, even a small imbalance in the currents can lead to feedline radiation. To prevent this I added a current choke at the feedpoint.
Now this is where a problem arose. The feedpoint is not supported, so a choke hanging from the feedpoint pulls the wire down creating significant sag in the wire. The original choke that was used was made from 3 feet (~1m) of RG-316 coax looped three times through four snap-on ferrites; it weighed 126 grams.
VP2E ready to deploy, showing new lighter air-core current choke
The world’s worst 80m Common Mode Current Choke!
When I decided to resurrect the VP2E I wondered whether I could improve the choke to decrease its weight. I chose to get rid of the heavy ferrites and build an air-core coil choke. I found about 9 feet of RG-174 coax in my junque drawer. I also found an old pill container made of plastic so light it almost defies gravity. After winding the entire length of the RG-174 around the super light plastic former I hooked it up to my NanoVNA to measure its effectiveness.
I ran a scan from 3 to 30 MHz and noted the attenuation across the HF bands. On the 10m band the choke is exceptionally effective with a common mode attenuation exceeding 30dB. On the other end of the scale, the common mode attenuation on the 80m band was a lousy 8dB. Well, the VP2E is a monoband antenna built for 20m, so the choke’s performance on 80m is not a concern.
Performance on 20m is marginal, but acceptable, at -20dB. Since the current imbalance is likely to be small 20dB of common mode attenuation should be quite adequate. And, the new choke weighs in at 67 grams, nearly half the weight of the old choke.
It’s stealthy too
Apart from its gain, another benefit of the VP2E is that it only needs a short pole for support. 4.2 meters (13.8ft) is the recommended height. My crappie pole is about 0.2 meters short but modeling the antenna shows very little impact – you work with what you got!
Where to buy a VP2E
This a real hobbyist’s antenna; you can’t buy it, you gotta build it! A 100ft reel of thin wire – I use silicone coated 22ga wire – is all you need. Cut it to the lengths shown in the diagram above. Solder the wires to a piece of coax feedline and you are ready to get on the air. Choke? I think it helps but you can use the antenna without one.
A versatile short, strong, light support pole
The center of my VP2E is supported on a 13ft crappie pole which is very light for carrying into the field. It is very strong too. Well actually, I threw away the very top sections of two crappie poles and a made a strong, light single pole out of the lower sections. It mounts on a fiberglass driveway marker pushed into the ground.
The exact same pole also works for my 40m wire antenna. It’s a low dipole built for NVIS (Near Vertical Incidence Skywave). More details on that in a later post. Stay tuned.
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