>Rich said:
>
>>With RF switching. the amplifier's RF relays can not begin transitioning
until
> >RF is >present. This is not good news.
>What about the situation where switching is done by PIN diodes? There must be
a
>finite time during which the transceiver and/or amp see a high VSWR, but this
>could well be short enough that it doesn't matter - provided there's no funny
>oscillations during it, which could give a key click effect each time the
>rx/tx transition occurred.
>
// No transceiver that am aware of puts out RF After the
T/R-transition starts. Thus, hotswitching on break is not possible. The
problem with a slow relay break time is that the relay may not be ready
in time for the next R/T-transition.
>You would also need to ensure that the switching took place at a low enough RF
>level that a 'soft' word (such as 'electron') still had enough power to
>switch - probably meaning a 40 or 50dB range on the switch, in which case the
>carrier leakage would probably hold it over. That shouldn't matter, though.
>
// RF-actuation is undoubtedly a looney-tunes situation. The
amplifier's RF-in and RF-out relays need to be fully closed Before RF
drive arrives.
>Where the transceiver uses relay contacts to control the amp, you can get
useful
>speed up by bringing out the relay coil drive, and using that to drive a
>transistor to switch the amplifier relay, rather than waiting for the
>internal relay to close.
>
// Amen to that, Peter. I removed the amp control relay in my
transceiver and replaced it with a 300V, 0.5A NPN transistor and 2,
1000-ohm 0.25 watt resistors. The price was under 40-cents. It's
fast, makes no noise and there are no contacts to burnish. However, the
NPN transistor will not key a negative-V.
>Although I have some suitably rated PIN diodes, I do have a certain (almost
>certainly unfounded) suspicion about reliability.
>
// With only a 1000 piv rating, high SWR or near field lightning could
be a problem for PIN diodes. Some years ago, a cloud-to-cloud lightning
discharge at a distance of 1-mile (5-second thunder delay) destroyed a
5000v ceramic doorknob capacitor in my 160m tuner. The good news about
vacuum relays is they recover reliably from static discharges.
However, PIN diodes are a whole nuther ballgame.
cheers, Peter
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|