I am certainly not in favour of any attempt to get
Icom to pay for the repair, and I think it very likely
that any such attempt would fail. After all the radio
is probably 10 years old. However, I remain convinced
that the problem was directly caused by a design
defect in the transceiver, and I see from other posts
that this defect is commonly found in equipment from
other manufacturers.
There is a major difference between happenstance rf
getting where it is not wanted, and a design 'feature'
that forces a potentially catastrophic feedback path.
The low level signal frequency transmit and receive
paths in the IC765 (and many, or most other
transceivers) use common circuitry. There is by
definition coupling between a transmit and a receive
antenna, and this coupling in the typical amateur case
may only be a few 10s of dBs. It would therefore be a
reasonable engineering decision to isolate a separate
receive antenna input from the low level transmit
paths when the rig is in the transmit mode. This would
require the use of a changeover relay (or equivalent).
Icom elected to use a single pole relay.
It is obviously very simple to put a relay externally
(or even internally as I did on my IC745 many years
ago), but the fact remains that it should not be
necessary. Neither should it be necessary to modify
expensive equipment to remove key clicks, or add
external interfaces because either the transceiver ptt
output or the amplifier ptt input do not meet their
published specifications.
Now I will climb down from my soap-box.
73 Roger
VE3ZI
___________________________________________________________
ALL-NEW Yahoo! Messenger - all new features - even more fun!
http://uk.messenger.yahoo.com
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|