Friday, February 13, 2009

Fake Diamond?

One reason why I decided to buy a Kenwood TH-F7E was that I thought it would be fun to try some FM satellite operation. I realized that I would need a better antenna for this than the supplied rubber duck, so after spending a lot of time comparing reviews of different dual band whip antennas with SMA connectors, and matching them with what was available at a reasonable cost here in the UK, I decided to order a Diamond SRH536 from PRJ Communicatons, who trade on eBay.

At least, that's what I thought I was ordering, though to be fair to PRJ, nowhere in their advertisement do they state that the antenna they sell is made by Diamond. However, the model number and spec are identical, and the antenna looks the same.

When I received the antenna the packaging states that it is made by Sharman multiCOM Ltd and the model number is WTA-SRH536. The name Diamond is missing from the antenna base as well. So I am guessing that it is not made by the same manufacturer, and its performance may not be the same.

As I am still awaiting the TH-F7E I decided to try the antenna out on my FT-817 using an adapter. The SWR is not great - three bars at full power on either band. Performance on 2m seems to be about 3dB down on a quarter wave telescopic whip, and also down on the FT-817's stock rubber duck. This is the difference between accessing a local repeater and not accessing it.

My SRH536 appears to work better on 70cm than the telescopic whip shortened to 5/8 of a wavelength, though that is based entirely on a field strength meter measurement - there are no 70cm repeaters within reach of this location. I couldn't compare it with the FT-817 rubber duck because the radio complains of high SWR whenever it is used.

I'm disappointed with the performance on 2m, which is the uplink frequency for the satellites, and wonder whether a different whip antenna would have performed better. I know that a short dual-band hand-held Yagi is the best solution for portable satellite operation. But that isn't portable enough for me, so I really wanted the best performing dual band whip antenna to use with a small HT.

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