Topband: Pro3 problem

[Herbert Schoenbohm]

Paul Beringer wrote:
> I recently built a hard line coax loop for RX and am pretty happy with it.However, my Pro3's RX antenna jack doesn't seem to have the feature to disable RX during TX. So what's happening on the coax loop is that it's getting RF back into the radio and causing the radio to disable power out.
>   
Yes Paul your PRO-3 radio protection features is being trigger by 
excessive RF on the RX antenna. Sometimes a series low voltage light 
bulb will help but a better solution is a positively driven relay on 
TX....not by RF but DC derived from the TX.

 With my PRO-3 I simply put a relay in a metal box with BNC connectors.  
The relay is 12 volts DC but the trigger for it on TX is drawn from the 
plus 8  volts which occurs on TX. The box also has a toggle switch to 
allow me to transfer the relay from external RX antenna to the straight 
through functionality.  I have tried to use the MFJ noise  canceling box 
backwards as a mean to provide a second RX port...and also other and 
other RF actuated devices but after to many complaints of chopped 
leading edge characters I stopped that.

On ACC-2 (If I recall) there is a plus 8 volts on TX which will 
drive...as in my case the Darlington pair of 2N2222 or equal...without a 
worry about the current demand of the relay.  You can get 12 volts from 
the same socket but it is not switched on TX and the current is only 
about 200 ma but enough for a small TX/RX relay which when configured 
will give you a RX separate port for the PRO-3.

Ever since Earl Cunningham, K6SE did a critical review on the Icom Pro-3 
I was sold on the fact that there is *not* a better low band radio the 
market today that, with the rebates and free supply, can get anywhere 
near the weak signal performance.  It has clean CW, so many so many 
firmware driven feastures, along with super DSP and just over $1200 even 
today with a switching power supply.  Only I just don't know why ICOM 
never felt it required to have a external antenna for RX......they do 
have other switchable antenna ANT 2 AND VHF with PL-258. but for TB they 
have never offered a mod....perhaps to protect the front end from 
RF...but a small pc relay circuit on their MB would have solved all that.

73,

Herb Schoenbohm, KV4FZ