Testing a new antenna. (GM/SS-125)

We have had horrible WX in the UK this last week, a huge storm, lots of flooding, gales and wind damaged, 6 people killed. Today the WX was lovely for late October, about 10C but a cold wind and blue sky…antenna testing time!

Andrew GM3VLB gave the components to me a few years back when he was getting too old to go island activating. There’s an adjustable loading coil (like a slidewinder), a coax connection and some wire radiators and radials. I have set it up before and found it would match on 40/30/20 but I have never used it in anger till today.

Usual drill and I was at the summit of Scald Law GM/SS-125 in 45mins. The wind was colder at the top. It took a few attempts to get the antenna setup and stay set. Then it was tuning time. KX2 tuner into bypass and Xmit selected. The loading coil was adjusted from its initial 23:1 SWR to 1.1:1. Then onto 20m CW. Well maybe conditions were up or maybe the antenna works well but I was busy with chasers. Both CW and SSB. 41 chasers with ODX being PY2BNL and second best WB2FUV, an S2S with IS0/LB5JJ, plenty of Europeans and some Ukrainian stations too.

OK, now from previous experience in the garden, I know if I can match it on 20m it will match on 30/40 but with the bands appearing to be good I tried 15m next. ATU activated and it took the match from 25:1 to 1.0:1 in a few seconds. Really? On SSB Czech Rep., Spain and Ukraine and on CW KA1R, WB8BHN, ND0C, N2AF, NE4TN and some Europeans. Finally I checked it on 10m and worked KC1NDQ and S52AU on SSB. I had another 2 hrs of daylight but I was cold so quit. Feeble I know!

So some pictures and descriptions:

Basic setup on the slope looking South West. 5m Decathlon fibre glass pole guyed around 1m. The loading coil is approx in the middle so 2.5m of wire above and below. You can see one of the 2x 5m radials laying on the ground running towards me.

The coax connector. Wing nut to attach the two radials. BNC socket for the coax to the rig. 2mm banana socket for the bottom radiator section. Teryy clip to attach it to the pole. The bottom section of the pole is covered with transparent heatshrink to protect it.

The loading coil. Attaches to the pole with 2 Terry clips. There’s another 2mm banana socket for the top radiator to connect to. The adjustable section looks like sliver plated wire wrapped around several small te wraps in series. The tiewraps are pulled tight and can be slid over the loading coil. The coil is wound on a Tufnol former 38mm in diameter, looks like 1mm tinned wire, 50-55 turns over 90m, the former is 112mm long. There’s a groove turned into the former so the turns stay in place.

Showing the wire from the wiper to the bottom connection and bottom radiation. Another 2mm banana plug attaches to the coax connector. An FMF index finger for scale :wink:

It was trivial to get a match on 20m and the KX2 ATU has such an enormously wide range it had no problems getting a 1.0/1.1 to 1 match on 15 and 10m. I’m sure this would be better if the feed point was raised but then there would be 1m less wire in the radiating section. We’re into the discussion we had with Ignaccio EA2BD and his short vertical. See Short loaded vertical antenna for restricted summits

Anyway this setup worked spledidly for a 1st attempt on a summit. It needs “SOTAising” so it’s a bit easier to deploy but seems quite promising.

Some nice WX pictures.

Carnethy Hill. It was one of those days when all the clouds had wonderfully fluffy tops and solid flat bottoms.

Black Hill GM/SS-167, just a few km across the valley. A trivially easy hill. Looking North-ish with bits of Edinburgh and Mid and West Lothian behind it.

A view of Scald Law GM/SS-125 from the overflow car park, everyone was out today so the normal car parks were full.

EDIT: I’ve just checked RBN and I was heard by VR2FUN-77 in Hong Kong on 15m.


Tried, but no joy from Arizona, Andy.

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I finished at about 1410Z. Another hour and conditions would probably have been better to the US Ken. But I was getting cold. I was also on the more Northern side so I stopped whilst I could still see the sun above the horizon. If I’d have been in the sun on the other side I’d have been in the strong winds. Sometimes you cannot win.


Great idea Andy using that style of clip to attach the coil to your pole save it flapping in the breeze. Good work.
Ian vk5cz …


Hi Andy,

A novel means of adjusting the coil. Probably better than the roller method.

Thanks for the info and pics.



Good looking antenna Andy, and works well! Thanks for the transatlantic QSO.

Randy, ND0C

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Interesting stuff Andy, and thanks for the QSO. You sounded well here.
Agree on the comment of an elevated feed point whenever possible.

Looking forward for a S2S with you using my short antenna as well.

73 Ignacio