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I've been pondering for a while what to do for a casual HF antenna for home use. Putting up a portable doublet when I need it doesn't really lend itself to a quick scan around the bands when I've got half an hour to kill, and the MFJ mag loop is pretty poor on 40m and doesn't cover 80m at all. I don't want a lot of overhead wires, and while there are trees around they are in neighbouring gardens, so it's a bit of a cheek to start suspending wires from them. So I started thinking about a loop antenna around the garden fence.... After trying M3XPR's W3EDP design, I'd been wondering about sneaking that up into one of the trees, but couldn't figure out how to do it.. then I started pondering a bit more... I started thinking a bit more... what if I took the measurements of the W3EDP, and laid it along the fence. It would get the feedpoint away from the house a bit, be pretty much invisible, and would be a good NVIS antenna if nothing else for local contacts. Well I set it up via my MFJ Z-11 Pro tuner, and after a couple of periods of casual operating I'm encouraged by the results. The wire runs through bushes and under a big tree, and is rarely more than 5 feet off the ground. But I worked GM4SSA in Shetland on 40m SSB with about 75 Watts and got a 5/8 report, and was really surprised to hear a W3 station last night - though I didn't even try breaking the pileup of 1.5kW Italian stations to see if I could work him. I've also heard a reasonable number of stations on 80m but haven't tried working any of them yet. The next step is to move the tuner closer to the feedpoint of the antenna, which will require some remote power - probably sticking it with an SLA gel battery in a waterproof box in the garden, and to see if 80m will tune better with the counterpoise disconnected (and if it does, find some way of remotely switching it). But if initial reports are anything to go by, the real next step will be to weatherproof all the connections as it's likely to be there for a while! And the lesson learned is that any wire you can leave out is going to make more contacts than something efficient that takes time to put up when needed. Update 1 Looking at the antenna with my Mini-VNA analyser showed it had a very odd resistance pattern with a very poor VSWR match at 80m. Since then I've moved the tuner into a plastic box in the garden to minimise line loss, and added a nice hefty earth stake. The earth stake has not only brought the noise on 80m down to a manageable S3, but means the match is better than 3:1 on top band, 80m and about 8:1 on 40m and 20m. Contacts on 80, 40, and 20 prove the antenna is working, including 59+30 from M3AFF in Devon with a nice high dipole. I still need to make the coax run a bit more permanent rather than hanging out the window, and possibly upgrade it to RG-213 instead of RG-58, and hide the wire a bit better, but I have a workable solution for the lower HF bands. |
