Hi Dave,
I don't remember my Mark V Field doing that with an Alpha 99 I had at the
time. I take it you have the Mark V that is 200 watt version? In the Mark
V Field unit there is a menu setting for limiting maximum power. I bet your
200 watt version has that same feature?? You might want to set it for 50
watts max if you have that menu setting and see if that helps. You might
also install a ALC line and just drive it so the ALC makes the power stay
where you want to drive the Acom. Are you FSK or AFSK?? On AFSK it could
be a mic or processor gain adjustment? That is all I can think of. I am
like you, I don't think the rig is suppose to do that. The power will
fluctuate, but not that much.
73 de w5jay/jay..
>I am using a pair of Mark 5 Fields to an Acom 2000A system in all modes.
> During the last RTTY contest I played at, I used the Fields at 40w drive
> and
> that produced about 1000w out. However there were 2-3 occasions when the
> amp went into fault mode because of "overdrive" and indeed the 40w had
> increased to about 60-75w which meant there was well over 2000w out...no
> wonder the amp faulted!
>
> Since that time I have been trying to understand the events better. I have
> found that both of the Fields react identically:
>
> If I set the RTTY output at, say, 50w using the digital, Array Powermaster
> and transmit....in about 3-4 minutes the output will increase to about 70w
> and plateau there. If I stop transmitting the power out may continue to
> rise
> say 5w . If I leave the rig for 15-30 min and then transmit, the initial
> value might have fallen back to 50w more or less.
>
> If I transmit again, keeping the output to 25w over the next few minutes,
> and then leave the rig alone once more, the output will have fallen to
> say,
> 4-5w!
>
> This does not happen with CW key down,,,
>
> The fans seem to be working fine and the heat sinks are just a bit warm to
> the touch...say, in the 80's deg F.
>
> I wonder if these observations suggest that the heat build up during
> transmission is causing the power transistors to have a greater output
> than
> normal? I have never heard of such a phenomena ...but of course, this is
> not
> my main field of endeavor. Has anyone ever seen this happen when using
> RTTY
> mode? Could it hve happened to others but remained obscure because we had
> no
> such digital precision in output meters?
>
> Will my only option be to "warm it up" first to reach plateau output and
> then set drive where I want it....seems unusual....hhmmmm
>
> 73 de David MD VE7KET
>
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