Hi Rich,
What happens if you put the exciter in transmit mode by closing the
PTT line prior to applying RF? We had a similar problem using the
FT-1000D driving an Ameritron AL-82 (slow buildup from a few
hundred watts to full output) over at the local club station. When I
would close PTT line prior to sending the leading dit with a keyer,
there was no problem (in this case the amplifier T/R relay closes long
before the RF arrives). I suspect the T/R relay on the Ameritron was
hot switching due to the slow contact closure from the FT-1000D.
During the hot switching, a large pulse of reflected power is seen by
the protection circuits on the exciter, causing it to fold back (it thinks
its looking into a high VSWR). If this is your problem, then you may
need some way to speed up the contact closure on the Commander's
T/R relay. Its funny that it doesn't happen on 160-20, but this could be
related to the length of the cable between the rig and the amp and how
your exciter's protection circuits respond to different impedances.
Try manually closing the amp T/R by using the PTT function on your
rig, or a shorting plug on the amp's control line. If you still get
foldback,
then you may have another problem.
73 de Mike, W4EF.................
----- Original Message -----
From: "Rich Hallman - N7TR" <N7TR@rnodx.org>
To: <amps@contesting.com>
Sent: Saturday, November 03, 2001 3:10 PM
Subject: [AMPS] Power problems on 10/15 Meters HF2500
>
> I just noticed that on 10 and 15 meters there is a slow build from a few
> hundred watts to the full 1500 watts when I begin to transmit. On CW the
> first few characters are low in power then build. 15 meters seems to take
a
> second or so, and 10 meters seems to be a bit worse.
>
> 20-160 meters is full power out with no problems. I have also tried
> another rig with the same results.
>
> Could this be an indication of bad 3cx800's? This is a Commander HF-2500.
>
> Thanks...
> Rich
>
> ******************************
> Rich Hallman - N7TR
> Reno, Nevada
> http://www.n7tr.com
>
> N7TR DX-Cluster Access:
> telnet://dxc.n7tr.com
>
>
>
>
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