At my home location, I have been on a quest for a decent multiband antenna that fits in my crowded back yard. By multiband, I mean a single antenna that does multiple bands well, without manually adjusting the antenna. Just switch bands on the radio, I do not mind needing to use a tuner, if the antenna will perform. I don’t quite have room for a fan dipole or a DX Commander with a proper radial field.
I have 2 antennas that are decent, and that both fit in my yard AT THE SAME TIME, each with some issues that effect performance.
1) My Hustler 6BTV (six band trap vertical).
Positives: It gives me vertical 10, 15, 20, 30, 40, and 80 meters with no need for antenna tuning. My radio’s internal tuner surprisingly gives me a good enough match on 6 meter to use it to hit local repeaters, even though I know barely anything is making out of the antenna.
Negatives: In reality, 80 on it is pretty useless, so it’s really a 5BTV. I was unable to mount it with an effective ground radial field, and use the fence as a ground supply. This works ok, but I know not efficiently. It’s location is also close to the garage with aluminum siding, and some trees that definitely effect performance when the leaves are out.
2) My EFHW-4010 end-fed wire.
Positives: It gives me 40, 20, 15, and 10 meters without a tuner, 12 & 17 with the radio’s internal tuner, and 30 meter using an external tuner. I’ve also been able to use the external tuner with it on 80 and 160 to fool my radio enough top use ft8 there but nothing else. It’s practically deaf there as it is not designed for it at all.
Negatives: I had to move the antenna 3 times before I was able to get at least one end of it high enough. (The manufacturer even says not to expect much of it under 30′ up.) Once I got it up that high, one end of it was very close to power lines, interfering on the higher bands especially. It also has the when-the-trees-have-leaves issue because of its location.
Between these two antennas, I can do a lot, and have been mostly happy with them a lot of the time. But we hams always want more. I keep looking for decent ways to get on 80 meter, for example, but I don’t have room for a full length wire. I also don’t particularly relish an antenna that is only for one band, or a third antenna crowding up the back yard.
But then I started paying more and more attention to doublets. One of the biggest performance issue with both my antennas is the long coax runs. When I do use a tuner, I know I am mostly just making my radio happy, and that most of my signal is leaking out of the coax on the return trip anyway. A major advantage of a doublet is that it uses balanced line such as ladder line or window line. With balanced line feeder, losses can be very low, even with high SWR, and the tuner can successfully redirect the returned power back to the antenna without much loss. The disadvantage for most people is that an external tuner is required, and running balanced line can be tricky compared to coax, Neither of these are issues I worry about.
But a good doublet is long. At least long enough to be near a half wave on your lowest band. And I pretty much already concluded that I’m not adding antennas unless I get 80 meter as well. So a doublet project was something I was reserving for if I ever move.
Recently, though, I started seeing people experimenting with linear-loaded doublets. A common trick is to build the doublet out of window line, and twist the wires together at the far ends so the current doubles back and electrically lengthens the antenna. Even doing this, the length may be pretty long for my yard if I want 80. Until I stumbled upon the concept of a “Cobra” antenna, which is simply adds a 2nd bend in the path (so the electrical path is now a “S” instead of a “C”. It looks something like this:
I have a spot I can fit a 40 foot antenna in, and it will provide a nice path for the window line to my shack window. Actually, I plan to run the window line to a 4:1 balun outside the window, and then run a short length of coax through the window to my coax-only tuner.
Parts are on the way. I plan to take pics during the build, and update the results here. If they are GOOD results, and I can get good performance on multiple bands 80-10, I will likely also make a video.
Moral: planning projects keeps your brain busy and distracts it from the angst of existence. I mean, Moral: Do stuff!