[AMRadio] In Defence of Old Buzzard Transmissions

Mike Sawyer w3slk at verizon.net
Mon Oct 12 13:43:18 EDT 2015

FWIW, I use a garage door 'Open-Close-Stop' switch box connected to P&B
latching relay. The relay mutes the receiver and keys the transmitter. When
I hit the Close switch, it breaks the latch and I'm back in receive mode.


 Do you have
> two separate sequencers in tandem, so that step 2 of the first 
> sequencer initiates step one of the second, or did you design the 
> sequencer to operate in three steps? Mine is two-step. When I first 
> actuate the switch to transmit, the antenna change-over relay, the 
> monitor scope and the VFO all come on instantly, as the receiver turns 
> off, along with the antenna shorting relay I use as an added 
> precaution to protect the receiver's rf input coil. In step two 
> following about 2/10  second of delay, the transmitter comes on. When 
> I switch back to receive, the whole  process is reversed.  One master 
> relay controls power to all the plate transformers in the transmitter, 
> so the rf exciter, modulator and final all come on simultaneously.  I 
> use arc gaps across the primary of the modulation transformer to 
> protect it in case the load is lost as a result of a failure associated
with the RF final.

I spent an entire day a few years ago experimenting with relays to come up
with a method that would best isolate the rx on transmit and
protect the input coil.   The way I do it now is almost too good
because I can't hear the 122 VFO for spotting on the CW rig.  On the
3-400 rig I spot with both the vfo and driver.   The RCA mod iron in
the rig also has arc gaps.

Like you, I use a  pilot relay to activate the
> big antenna change-over, since its heavy-duty coil is 115 volts a.c. 
> while all the rest of my relays run on about 30 volts d.c. The main 
> purpose of my sequencer is to avoid  hot-switching the antenna 
> change-over relay, which was burning up the contacts.

I put a large P&B 4PDT 24 v. relay in a die cast aluminum box for the main
T/R relay.  It is made with copper arms, silver contacts and brass/aluminum
lugs.  3 poles handle RF; the 4th one is used to short the rx line to ground
on tx.

> Speaking of annoying and chaotic, the very worst has to be to operate 
> AM using VOX, particularly making long transmissions with the carrier 
> dropping out and back in at every pause in speech.

AM VOX is one thing I have yet to hear (fortunately).


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