mercoledì 6 aprile 2011

Boost your HT for almost nothing

As almost every ham radio operator, I’ve a small portable radio. According to QRP philosophy, I choose to buy a Yaesu VX-2: very small, not very expensive, max power 2.5W with built-in battery. Using this nice radio I feel a bit frustrating for the short range of the communication allowed. The first thing I’ve done is changing the original useless rubber duck antenna with a telescopic quarter wave, and the results were very good. Navigating Internet, in HamUniverse Antenna Projects (in particular an article by Edward KE4SKY,, I’ve found another nice (and cheap) improvement to try: a quarter wave counterpoise.

The trick is trivial, and is surely well known to all hams operating in HF: a quarter wave vertical MUST be used with a good ground plane or against one or several counterpoises. This is true also in VHF region, but what is the amount of improvement? I soon arrange a quick-and-dirty counterpoise for my VX-2: 49 cm of speaker wire wrapped around the SMA antenna connector: the improvement in RX seems to be incredible, better than 1 s-point, in some conditions even 2 s-points!

The performance improvement is significant: we can note that 1 s-point is 6 dB; this means that my VX-2 with quarter wave counterpoise is more powerful that a 5W HT without counterpoise. In TX same situation: other hams reports that is a +1 s-point when I use the counterpoise.

I’ve built a more clean and stable version: a 6mm ring terminal and 49 cm of RG-174 (only braid connected). The 6mm terminal fits well in the SMA connector, and screwing the antenna lock counterpoise firmly in place.

I’ve also built a two band version, using speaker wire, one of which cutted at 17cm and the other at 49cm, the performances are a little better on 70cm. In past times, it was a commercial version of the counterpoise, which is called “Tiger Tail”. In the foto below, the two "tails":

The counterpoise is useful for all kind of quarter wave antenna, even shorted quarter wave or rubber ducks. Of course, I try also many conventional 5W HT, with the same (good) results in terms of performances. In UHF the improvement is less noticeable with my telescopic antenna, which is a half wave on 70cm.

This simple trick really performs well, is very cheap and fast to build. I’m surprised that is unknown by most ham radio operators. Try it!

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