[ICOM] is there some sort of protector on the RX ANT, input of a 756 Pro?

[Gary P. Fiber]

I am not sure of the newest Icom products, but I can tell you the 
earlier radios, IC-745, 751 / A, 761. 765, 781.... NONE of them had any 
sort of protection in the receiver input.
If you removed the coaxial jumper and attached your receiving antenna to 
the Receive Antenna In jack, you were connected directly to the receiver 
front end.
Use of some sort of protection or relay circuit to remove the RX antenna 
during transmit was always recommended at least by myself when I worked 
at Icom.

Using the UHF (S0-239) connector there is a small relay between that 
connector and the Receive Antenna Out jack.
During transmit that relay would open placing an air gap between the 
Transmitter output and the Receive antenna input so the receiver front 
end would be protected.

I was never sure what the reasoning was for the ability to open the 
circuit to having an unprotected receiver input, maybe a preamp.
So the long and short of it, if you attach a fine receiving antenna to 
the receive antenna input you need some sort of signal attenuator that 
operates when you transmit.
Sending 100 or 1500 Watts out your transmit antenna will certainly cause 
you likely high millivolts of RF energy presented to the receiver input 
being picked up by your receiver antenna.

Gary K8IZ.

On 2/9/2011 9:56 AM, Carl N9GC wrote:
> The 756 line has long had a history of that sort of failure. Burghardt
> Electronics built a protection circuit for this purpose a number of
> years ago. They only repair rigs now but may still have the protection
> circuit available.
>
> 73, Carl N9GC
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-- 
Gary P. Fiber K8IZ

General Radio Telephone Operators License PG-19-6691,
with Shipboard Radar Endorsement.
Washington State Resident.

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