n Dec 11, 2008, at 11:55 PM, Gary Smith wrote:
> I received reports my signals were seen on multiple
> frequencies at the same time and there were poor characteristics to
> both CW and SSB. The problem was only when using the remote
> antenna, unplugging the
> remote antenna resolved the issue....
This is a more general problem that is commonly realized, and it can
happen with many different station configurations whenever the
transceiver has a separate RX ANTenna input in use. The problem is
that the RX ANT input is often left floating when the rig is
transmitting. Signals appearing at the RX ANT during transmit periods
can become coupled to low level gain stages in the transmitter chain
-- through bundled wires inside the transceiver, neighboring copper
traces on shared circuit boards, excessive ground trace impedance,
etc. Observable symptoms will vary from rig to rig, but may include
randomly varying ("wandering") SWR seen by the transceiver's SWR-
monitoring circuitry. Long Beverages and antennas with preamps (such
as described by KA1J in his posting) can put rather large voltages on
the RX ANT terminal unless somehow grounded or otherwise inhibited
during transmit periods.
Some Kenwood transceivers exhibit this behavior, and I believe (but
have no direct experience) that other hams have had to resolve it for
certain Yaesu models. It would have been nice if manufacturers had
simply added or utilized a relay contact on the internal Main ANT T/R
relay to ground the RX ANT input.
Keep in mind that during transmit periods the strongest signal on your
Beverage or other receiving antenna is likely to be your own signal.
Bringing your own RF back into the low-level stages of your
transmitter (via the RX ANT input and unexpected coupling paths) can
potentially lead to positive feedback and unstable operation -- what
The Old Man would have classified as "Rotten Signals".
Congratulations to KA1J for caring about the quality of his
transmitted signal, and for diagnosing the source of the problem.
Bud, W2RU
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