[Hallicrafters] B&W TR switch

[Kevin J Ward]

Recently Parker Buckley wrote about problems using his B&W 381C
electronic TR switch.  I've been running full break-in (QSK) with an
assortment of transmitters, receivers, and TR switches for 45 years, and
one of the things I've learned is that a TR switch, when used by itself,
will not provide smooth break-in.  Proper receiver muting and transmitter
control are also needed.

Unless the gain of the receiver is reduced while the transmitter is
actually transmitting, the receiver will be overloaded.  Feedback, loud
and distorted audio from the speaker, clicks, thumps, and more will make
the setup unusable.  The TR switch's job is to protect the receiver
front-end from actual damage when the transmitter is on, and couple the
antenna to the receiver when the transmitter is off, nothing more!

Complications arise when we try to use a transmitter in which the output
stage is always drawing plate current.  Most SSB transmitters used on CW
operate the final as a linear amplifier.  When the transmitter is in the
MOX or manual transmit position, the final is drawing static plate
current.  Even class-C rigs that use a clamp tube draw some static plate
current.  This generates copious amounts of wide-band noise that the TR
switch feeds directly to the receiver, effectively masking received
signals.  One solution is to use the VOX function to turn the transmitter
on, and perhaps even use the VOX auxiliary contacts to reduce the
receiver gain.  For true QSK operation, it will be necessary to modify
such a transmitter.  There is an excellent screen-switching circuit that
was designed to work with the Collins S-Line, and it provides smooth CW
break-in without affecting phone operation.  I'll be glad to look up the
article for anyone who is interested. 

Last, but not least, a TR switch is useful no matter what mode you
operate, and it is NOT limited to CW.  You just have to add all the
necessary ingredients.

Kevin   N2IE

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