Monday, July 1, 2019

Rowland ring feed experiment

Diagram by VK3YE
When reading a article about feeding a simple conducting pole on VK3YE's blog. I immidiatly felt the need to experiment with this. Remembering my thoughts about feeding a large streetlight pole in front of our house when I just started with the radio hobby (1979). Wouldn't it be nice to have a universal system that could feed al kind of conducting large material like masts, poles, railing. A that time I was told a gammamatch would be capable of this task. But you can't drill a hole for a screw or whatever in public poles/masts streetlights of course, so a gammamatch is just out of the question. But now I found out about the Rowland ring. Officialy invented by Henry August Rowland as an experimental arrangement for the measurement of the hysteresis curve of a sample of magnetic material. In the vietnam war it was experimentally used by the US army to feed trees as huge verticals. This experiment was repeated in a art project by PA1RB. VK3YE Peter experimented with it loading up a football goal pole and a railing, in the drawing he mentions a clothes hoist. This would really be a nice experiment, very simple and easy. The only thing you need is a big capacitor (found one lately on a radio rally) and 5m insulated wire which you wind 33 times on a 40mm tube to get a coil.

Well, since it was mentioned in the drawing, I started testing a clothes hoist. I already expected it would not be suitable for HF but could be for VHF. Best SWR was on 62 MHz but a 1,8:1 match could still be achieved on 145 MHz. Second experiment was loading up the  16m antenna tower, I was not impressed with only one dip 1,8:1 on 10,140 MHz. Actually I expected better results...

So, in the Vietnam war the USAF experimented loading trees with this method to communicate over short distances. I don't expect too much from a tree antenna but as a experiment loaded up the largest tree here which is about 20m long. I was surprised I got a very good dip of 1,2:1 on 7,1 MHz. I decided to connect my FT-817 now and started to listen. I received reasonable signals from a station in Frankfurt and one from the Orkney Islands. I tried to make a contact but it didn't happen and I was out of time. Since this is interesting enough to continue experimenting I could try to do some WSPR and measure if the tree is really radiating. I time allows I will certainly try it and will report on t his blog.








4 comments:

  1. This is interesting, I would think that it would work best in winding a coil of insulated wire around a mast of some kind and then the coil tuned for resonance.

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  2. If you read the PA1RB article and view the photos you can see they used a rather large coil around the tree...73, Bas

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  3. Oh no! A fascinating idea I will now have to try! I'm heading straight for the pine forest...

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    1. I think it is all in the name.....go for it....73, Bas

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Thanks for your comment. Bedankt voor je reactie. 73, Bas