[ICOM] AMP INTERFACE TO 756 PRO II (CONTINUED)

[Larry Benko]

Paul,

I 100% disagree with you.  I have measured several Icom rigs (706mkIIG, 
746, 746PRO, 756, 756PRO, 756PRO2, 765) and on all radios both the 
"SEND" line and the relay precede any RF by 9 to 11 ms. on key down and 
both remain active for approximately the same time after the rf quits on 
key up.  I have made some postings to this reflector with the absolute 
data in the past.  Search on my call to find it.  If you have evidence 
based on scope measurements (do not run scope in alt. channel trigger 
mode) please post it.   My amp is keyed directly from the send line 
through a transistor buffer allowing more than 1 radio to key the amp. 
and have never had any problems.  If you have problems I would suggest 
you try the experiment when operating into a dummy load.  If your 
problems go away then the problem is RF getting into the circuit.  While 
RF might get into the send line a relay is much more RF resistant.

73,
Larry, W0QE

paul at w8aef.com wrote:

>> The exciter probably applies RF a few mS after extending a ground on the
>> SEND line. One could shorten this interval by using the ACC(2) Pin 3 
>> SEND
>> line to turn on a solid-state buffer, which would in turn ground the 
>> amp's
>> PTT line.
>
>
> I found that on my PROII the ACC(2) Pin 3 SEND lead releases before 
> the PROII's rf ends.  The symptom was that while operating QSK my 
> Alpha ran at reduced power output.  Actually it was the ALC in the 
> PROII seeing a (momentary) open circuit and the antenna spigot and 
> shutting itself down.
>
> The cure was to go back to using the PROII's relay output to key my 
> amplifier.
>
> de Paul, W8AEF
>
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