Greetings,
According to the *QST* Review of the IC-706 (March '96, page 65), 'Rus'
Healy, NJ2L, said: "The radio will not key an amplifier relay directly. You
need an external relay or switching circuit like the one in *QST*, November
1995, p 84, 'Cure for the missing First Dot Problem...' "
73, Glenn, KB1GW
ARRL HQ
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>From: AA6KX
>To: cq-contest
>Subject: Output Spike on Icom-706
>
>Return-Path: <AA6KX@aol.com>
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>In preparing for an upcoming CONTEST expedition for WPX, I recently set out
>to test my new Icom 706 with my Alpha 87A.
>
>Anyway, when I try to drive the 87A with the 706 I see some very unexpected
>behavior. No matter how low I set the drive power on the 706, the very
first
>dit I send causes the power output lights on the Alpha to flash full scale.
> Succeeding dits which are closely spaced will give the expected power
>reading based on the amount of drive supplied. In SSB, a similar situation
>holds. I can pull down PTT so that all the T/R switching is complete but
>then the first bit of audio supplied causes a momentary full-scale reading
on
>the 87A's power meter. After that momentary flash, the reading is
expectable
>in the same way as it is in CW.
>
>I first contacted Icom Customer Service about this and they had no
>explanation at all. Their representative mentioned K1KP's article in the
Nov
>'95 issue of QST on using a optocoupler for T/R switching, but even he
>acknowledged that the problem I was seeing didn't sound like a timing
problem
>with T/R switching. This morning I contacted ETO Customer Service (Ray
>Heaton), and he gave me what I think is a totally plausable explanation.
> This is that the 706 is actually putting out a momentary spike when it
first
>starts transmitting that is full-scale (or worse) output. Some time delay
is
>required for the ALC circuitry in the 706 to kick in and cause the output
>power to be cut back to the proper amount. This time delay is in
>milliseconds, of course, so a peak-reading wattmeter is not fast enough to
be
>able to record it. The LEDs on the Alpha do show it, though, and Ray
>suggested that I was risking damage to the PIN diodes in the Alpha if I
>operated it with this initial spike coming down the line from the 706. He
>suggested that what I really need to do is use a scope to measure the size
>and duration of that leading spike and then go back to Icom with the
>information.
>
>This sounds fine, but I don't have access to a scope these days. So, for
>those of you with the perseverance to read this far, I wonder if there's
>anybody out there with a 706 and a scope who would be willing to take a
look
>at this for me? Alternatively, I'd eagerly be willing to go anywhere in
the
>SFO bay area to set up a test with my 706 if you have a scope we can use.
>
>Bruce Sawyer, AA6KX
>
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