Chinese hand held radios
Optimise the antenna on your cheap hand held radio
Have you got one of those cheap Chinese hand held transceivers that you
see sold on eBay? You have! Well in that case have you ever checked that
rubber duck antenna on an analyser? If the answer is no maybe you should.
Cheap hand held radios are flooding into the UK through eBay and names
such as Wouxun, Jingtong, Puxing, Linton and Quasheng are becoming
familiar to radio amateurs around the country. I must admit that at
first I was very sceptical about the quality of these radios, but when
you check them out they turn out to be in the main of at least
acceptable quality. You can of course get a duff one but most people I
speak to have been very happy with their purchases. There is no doubt
that you tend to get what you pay for but putting a few of these radios
through their paces has shown them to be at least as clean and sensitive
as their more expensive Japanese rivals.
Discussions down at the local radio club and on air has lead me to
realise that a lot of amateurs are using these radios straight from the
box and are wondering why they are such a poor signal into the local
repeater. The problem lies not in the radio but in the antenna and the
wide band nature of these sets. The popular four metre Wouxun 689E for
example actually comes two antennas and the set covers 66-88MHz receive
and transmit. One antenna is for 66-77MHz and the other is for 77-88MHz.
For use on the 70MHz amateur band the first antenna is used but try it
on an antenna analyser and you will see what would be normal considered
a somewhat poor match. Looking at some of the other Chinese hand
portables we find the VHF ones cover 136-174MHz which is nearly 40MHz
band width on the one antenna, have these guys discovered something we
do not know? Unfortunately not! The UHF sets are even worse with some
covering 320-470MHz on a single antenna. No wonder they seen to be poor
performers. The fact that theses sets work at all straight from the box
is probably testament to the bulletproof output circuits on the rigs alone.
The answer to this problem is simple if you have access to an antenna
analyser you can simply remove the little plastic end cap on the antenna
and trim the antenna to resonance and the glue the cap back on
afterwards. The result will not be Earth shattering but you will at
least be putting out most of the rigs meagre power instead of a few
milliwatts. While a rubber duck is no alternative for a proper antenna
it may just be enough to make that ‘scratchy’ signal into your local
repeater fully quieting.
If you don’t have access to an antenna analyser you might think about
joining your local radio society/club or asking around on the air. Some
radio amateurs have been known to actually be quite helpful. The
alternative is to buy a rubber duck aerial that is meant for amateur use
but that could cost you more than the radio and there is no guarantee
that what you buy has been optimised for the band. For example, a lot of
two metre antennas are sold cut for the American market and might be
tuned for anywhere between 144 and 148MHz were as we might want to
optimise ours for 145MHz. If you trim your own you can at least cut it
for wherever you want to operate, which I feel is a better solution.
Even better and more fun is to make your own but that is another story.
Steve Studdart GW7AAV
This article was published in the July 2009 copy of RadCom, the RSGB's official magazine.