[Icom] Spike on transmit: Pro and L-7

[Joe Moraine]

I received the following message from a fellow ham in Finland who is
using an N8MIS amplifier interface between his IC-756Pro and Drake L-7
amplifier.  I tried the test on my identical setup and notice no SWR
spike at all on initial key up.  Does anyone have any ideas what might
be causing his problem that I can pass on to him?
Thanks for any help,
Joe, W5LX
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Hello, Joe.

Ref. our discussions 6 months ago I acquired N8MIS outboard relay and 
it seems to work OK. 

I wonder, if you still have IC-756 PRO + Drake L7 combination, 
so that you could make a following test? 

Only recently I found out (poor reading of the 756 PRO II manual!) 
that I could have all the meter readings as bar-graphs. All concurrent 
meter readings looked good except, when using the IC-756 and the L7 
on CW. Pressing the key would momentarily bring the SWR reading up 
to more than 3:1 and then quickly return to a normal value . 

Do you see the same phenomenon? As if there would no full connection 
in the circuit IC-756 - N8MIS - L7 before the transmission starts? 

Funny thing is that I do not notice it on SSB when pressing the tangent 
of the SM-20 microphone. 

With the plain IC-756 PRO II on-line, no such action of the SWR reading 
occurs on either mode. It goes directly to the normal SWR reading.

If you still have the 756 PRO and L7 and N8MIS relay in between with 
no ALC line connected in service, could you make a similar test? And 
what your bar graph meter shows? 

What could be the explanation and possible cure? The L7 is unmodified 
(except the fan changed) and works since 1981 here. 


73 and have good week-end.
Tapani/OH2LU
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