[AMPS] hot switching

[David J. Riehl]

Hello, everybody, I'm new to the reflector, but have been following some
of the threads for some time now.  I've reviewed much of the literature,
even back into the '60's and am wondering whatever happened to the
QSK/TR approach written up by Dick Frey, K4XU, in April '78 HR 
magazine?  (This also appeared in the ARRL Handbook until the mid-80's,
as I recall.
Advantages IMHO:
1)No need to make/break contacts which will carry the high-power RF.
  The amp is always connected to the antenna.
2)Only items requiring switching are the grid-bias and (maybe) the 
  receiver protection circuitry.
3)In receive mode, peaking on the noise, will normally get the amp
  within 5-10% of tune.
    
Disadvantages:
1)Requires a lo-capacitance connected to the hi-Z end of the amp's
  pinet, for the receive tap.  INSTALL WITH CARE, NOT FOR NEOPHYTES!!
  Also this connection is frequency sensitive, but should be good for
  a 20-and-up, or 2:1 frequency range.
2)Requires separate receive antenna port on the transceiver or 
  separates.  Most modern rigs provide this.
3)There is some attenuation on receive, but an inexpensive pre-amp
  should overcome this as well as provide another "layer of protection"
  for receiver front-end.
4)There is possible damage to the receiver port if the protection fails,
  but this is not likely, if done properly.
      
QSK TR switching for the receiver port (well under 100w) could be
implemented by a medium-power RF reed relay, a simple SPST pin-diode
switch, or an electronic TR switch (tube or FET).
   
I'll try to keep future posts briefer, but this subject has been on
my mind for a while now and I wanted to do it justice.  I'm am really
hoping that a number of the experts, who have been involved in the
evolution of the art, can enlighten us as to why this approach is not
used (to speak of) in ham gear and whether it might be updated to be
fully useful at this time.
           
73,
Dave Riehl   AF5B

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