Saturday, May 15, 2010

10m portable whip

My reason for getting the Intek H-520 Plus hand-held was to try to work some Sporadic-E DX from the great outdoors. I didn't think the supplied 18cm whip would be much good for that so I looked for the longest 10m BNC whip antenna possible. The best I could find was the AT-10 with a 4 foot telescopic whip which I believe is made by Sandpiper Antennas in Wales. It is sold by Waters and Stanton. I ordered one yesterday and it arrived in the post this morning - nice to see they can get it right sometimes.

The first thing I did with the antenna was put it on my AA-200 antenna analyzer. I was dismayed to find that the SWR on 10m was more than 10:1 and the best match was around 38MHz. I anticipated that this would be going straight back. However the instruction sheet "Getting the best out of your antenna" recommends using it with a counterpoise. I had expected to use one for best performance anyway, so I decided to try this before writing the antenna off completely.

The instruction sheet recommends a length of 6ft 5in for 10 metres, but I found that was too short as the best match was still well above 30MHz. By trial and error I eventually found a length of 7ft 6in was about right. The best SWR was still only 2:1 so I think the antenna is capable of improvement, but there is nothing else available to the best of my knowledge.

If a counterpoise is required you might think it would be a good idea for the manufacturers to provide somewhere to attach one. I tried using an alligator clip but it tended to slip off the BNC connector. In the end I managed to solder to the outer sleeve of the BNC connector using my biggest soldering iron turned up to maximum temperature so the counterpoise is now permanently attached to the antenna (until the wire breaks off, which it will probably do in the middle of a field just at the start of a massive band opening.)

Now I just need some Sporadic-E to see how far it is possible to work with a hand held radio.

1 comment:

Steve GW7AAV said...

Sandpiper make some brilliant antennas but I had a similar problem with a 2m/70cms mobile whip from them. I had several antennas damaged or stolen from the car at the time so I bought a low profile dual bander that was a quarter wave on 2m and 2 quarter waves on 70cms. It was worse than my home made quarter wave so I threw it to one side for about ten years. About a year ago I got the use of the radio clubs analyser and I could not find a single frequency the thing would resonate on. Best I got was about 20/1 on 338 mHz. Caveat emptor as they say. You seem to be having more than your fair share of duff buys lately.