Monthly Archives: August 2013

Frying antenna wire with QRO

RF Weld - Click to zoom

RF Weld – Click to zoom

In the process of testing out my 80m coil this morning to load up my 40m vertical, I pushed 400w AM up the antenna and the ACOM went into alarm, telling me the SWR had gone too high.

Upon investigation, I noticed that just at the top of the coil, as the D10 comms wire kinked around some insulation tape and started its travels vertically, the wire had welded apart.

I made a repair using extra heavy gauge copper to take the high high current and all seems well again.

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Adding a loading coil to a 40m Vertical for 80m operation

80m Loading CoilA successful morning today to convert my 40m vertical to an 80m vertical by adding a loading coil that I can switch out manually by just unplugging it. Nice and simple.

It’s not a great SWR curve due to the loading coil but I achieved 1.8:1 SWR at 3.79 Mhz, ideal for DX.

For the techies who want the dimensions: I wound 24 and a half turns on a fibreglass 2 and a quarter inch fibreglass former. The length of the coil itself is 3.5 inches.

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Tuning a vertical antenna with the ocean tide

cornwall qthHere’s a new one that you wouldn’t read in the books.

I’m seriously hammering the 40m band here in Cornwall and have tuned the vertical antenna so that the whole of 40m SSB is almost 1:1 swr, certainly from 7.05 through to 7.1Mhz. Over the last few days though, I’ve noticed that the tuning might change over a few hours to give me some serious SWR headaches. Enough to force me at one point to fold back the top of the element by 70cms.

It took me a while to track down what was happening but it turns out that when the tide is in, the vertical is effectively closer to the salt water ground and requires to be shorter than when the tide has been out for a while, long enough for the salt water to drain out the sand and reduce the salt water table by probably 15 to 20 feet or so.

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Amateur Radio with low electrical noise

40m and 20m verticals

40m vertical (left) and 20m/10m Nested Vertical (right)

I’ve been running many pile-ups on 40m this week and I think half the reason is that I can hear so well because the electrical noise is almost non-existent. Of course, my TX is also pretty good because of the salt water too.

Working conditions; My “holiday” rig, Kenwood TS-2000, Heil Goldline, NC10 netbook running N1MM “DX” mode with a RigBlaster for voice keying and my Acom 2000 to loaf around on.

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40m Quarter Wave Vertical, Cornwall

40m vertical

Quarter Wave Vertical 9.6m in length

I’ve tried many verticals and never had good results APART from this one.

This is a 9.6m long fishing pole and the length of radiator is the same. I fixed 16 x 10m long radials to an insulator that I had lying around. I would have preferred this to have been aluminium but I already had three of these. Most of these bits were salvaged from the three-element vertical array with raised verticals that James and I made back in 2009. Each bolt was bonded together with some copper wire that is out of shot, underneath the insulator and the radials were politely scattered in an approximate radial system on the ground. SWR is 1.0:1 according to my electronic controller on the Acom 2000.

The results have been amazing but I do realise that I had two things on my side; location by the sea and almost no electrical noise. Bliss.

As I write this, I’ve worked 48 DX entities over about 7 hours operating time on 40m. Quite incredible. I’m a convert.

Nested Quarter Wave Vertical Antenna 20m and 10m

20m 10m verticalWith my recent success at building fan dipoles that are more “nested” than “fan”, I saw no reason why I couldn’t put up more than one element on my 20m band vertical to achieve a match on 10m. I ran up a 2.4m length of D10 comms wire up the side of the pole, around 2 inches away from the 20m quarter wave element. After trimming a few centimeters here and there, it tuned it at 1.3:1 SWR and all was well.

To make sure everything really was good, I applied a QRO carrier and watched in amazement as the SWR hovered for a few seconds before moving up and down and finally going off the scale with the Acom shutting down with an alarm (what a great amp that is!).

It took a while to track this down but it turns out the D10 military comms wire had melted at the guying point about half way up the 10m vertical element. I had tensioned it around one of the bolts on the steel three-way guy point to stop it flapping around and it decided to try melt the insulation and finally and weld itself onto it before blowing itself apart. The joys of QRO.