How to make a stealth amateur radio wire antenna

Until recently, I had a) a 40m triangular loop in the back garden which I called a “micro-mega-loop” and b) a 60m loaded loop that allowed me to get on 80m. The two loops looked a bit horrendous not only because of the wire in the air, but because I used halyards to lift them in the air to the top of wooden stair rails. It was all very messy. They were also extremely close together along the back of the garden which meant some of my RF was absorbed by the other loop. See here: http://www.m0mcx.co.uk/sg-230-feeding-60m-skyloop-deltaloop/

DSC_0217I like loops for two reasons, a) for my small garden plot, I can achieve in half the size, what other do with a full size dipole and b) a resonant loop will also resonate on every harmonic, that means tuning a 40m loop at 7.1 Mhz means I also get 14.2, 12.3 and 28.4 Mhz.

The bigger loop utilised the loft / attic space and at the time of installation, about 10 years ago, I was worried about visual impact so most of the antenna ran along the inside of the loft, popping out at gutter height. Not only was this probably pretty inefficient – but I didn’t have the WARC bands either.

Recently, I cut out the loading coils off the bigger loop and installed a high-power feedpoint ATU (800w PEP). For 6 months now, I’ve been enjoying the WARC bands, particularly 30m band and the ATU has proved reliable – certainly reliable enough for me to have the confidence to take both loops down and construct a much better one.

DSC_0190I’ve been spending time buying up redundant 4.6m sailboard masts off eBay of late. This is harder than you might think. Most are still expensive and the seller normally wants them collected. Some negotiation is normally required for a successful purchase under £40, however, they are ideal wire antenna supports. I painted a pair camouflage colour using some matt paint from Halfords. It’s pretty amateur but seems to keep the neighbours happy.  There’s a bonus that most sailboard masts (not all) seem to happily slide over a standard 48mm scaffold pole.

Stealth Loop Antenna

My new (only) loop is 62 metres D10 comms wire fed through the loft but with 16mm holes drills right at the eves to allow 15mm plastic water pipe to thread through them. This allows the D10 comms wire to easily go through and also supplies some springy strain-relief when the wind blows. The loop goes to the bottom of the garden, through some cut-down dog bone connectors and then straight back up to the loft. No halyards this time. It makes maintenance slightly harder but the visual impact is great and I achieve the maximum size of loop for the garden space.

I feed this “random” loop my high-power antenna tuner, similar to the SG230, which I use to run the 200w vertical. However, the one I use in the loft is from MyDel, apparently now a defunct model, the CG5000. This gives me 400w continuous, ideal for high power RTTY and I’m all-band from 80m through to 6m – including WARC. Computer modelling suggests some strong gain on a number of compass points, particularly on the higher bands. Of interest, although the MyDel spec doesn’t claim to tune up 6m, I do actually get a tune of under 1.5:1.

Achieving the height in the garden was easy with the sailboard masts at around 7.5 metres to the tops and inside the loft, about 8.5 metres. Quite high compared to my previous attempts with wooden hand-rails designed for stairs (which bent over the years into a kind of banana shape). There are again, simply bolted to the garden fence posts using screw threaded coach bolts.

A couple of tips if you are thinking along similar lines: I “gooped” up the hole inside the 15mm water pipe with a small amount of mastik. The D10 comms wire can still “float” inside but hopefully the wasps won’t find it. I also used some special plastic inserts at the ends of the plastic pipe so that the raw edge of the pipe was smoothed out so not to wear down the D10. Plumbers use these inserts when using “speed-fit” connectors. They are “cheap as chips” for a bag of 10. B&Q sell them.

I also applied more strain relief to the antenna in the form of some 14mm elastic cord near the feedpoint attached to the D10. This should partly eliminate issues when we have the winter storms. This “bungee cord” *and* the springiness of the plastic pipe should give enough to keep everything pretty stable and reduce the potential for a wire-snap.

Results:

Too early to tell but all bands tune fine and tonight on the 80m ROPOCO contest, the big loop loafed along just fine. One blast of RF to tune the ATU at 3.7Mhz gave me 200Khz bandwidth at below 1.5:1.

73. de m0mcx