> Recently, though, I had some 160 m antenna
> problems under high power and blew the fuse lamps that protect the rx
> PIN diodes.
Wrong ... the fuse lamps protect the transceiver if the "receive"
PIN diodes or HV power supply fails and amplifier RF gets through.
They are also there to prevent the amplifier from running away in
the event of a diode/HV failure.
> I'll check the schematic, but does anyone have an idea or two about
> what might be going on?
Check D2, D3, D4 and D11. Also make sure that the high voltage is
present on L6 in transmit. Flashing of the fuse lamps indicates
that RF is getting back from the output of the amplifier to the
transceiver. D2/D3/D4/D11 should be reverse biased (through Q3)
in transmit and forward biased (through D6 and Q4) in receive.
If you had a high SWR or arcing situation, I would expect D4 and
D11 to short and significantly impair the isolation between the
antenna (amplifier output!) and transceiver during transmit!
In the QSK-5, D1 is the normally open path from transceiver
to the amplifier input (drive). D2/D3/D4/D11 is the normally
closed (amplifier bypass) path between the transceiver and the
antenna, and D7-D10 are the normally open path from the amplifier
output to the antenna (RF Out).
73,
... Joe, W4TV
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Kim Elmore
> Sent: Saturday, January 31, 2009 8:55 PM
> To: amps
> Subject: [Amps] Internal QSK-5
>
>
> I have an AL80A with an internal QSK 5 switch (one of the early ones)
> that I've had since new (S/N 095). For well over 20 years, it's been
> working flawlessly. Recently, though, I had some 160 m antenna
> problems under high power and blew the fuse lamps that protect the rx
> PIN diodes. Blowing these is no biggie as it's happened before when I
> mis-selected an antenna or has a switch set wrong. I replace them and
> go on my merry way.
>
> WIth K3LR's help, may 160 m antenna seems to be going again. So, as a
> final smoke test, I stated testing it under high power. But, this time
> I'm seeing the fuse lamps light up when I transmit with more that a
> few hundred watts on 160 m into a dummy load. I don't see this on 80 m
> or any of the higher frequencies. As far as I know, this is new,
> though I've never had much of a 160 m antenna and so didn't use the
> amp it much down there.
>
> I'll check the schematic, but does anyone have an idea or two about
> what might be going on?
>
> 73,
>
> Kim Elmore, N5OP
>
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