[Boatanchors] T/R switch question _ 221122

[w8au]

Bob, the B & W TR switch is simply a Vacuum tube rf amp
tied to the xmit line that saturates under xmit conditions
and limits the rf level to the rcvr input. Some TR
switches have a broadband toroid output transformer that
generally covers the HF bands.

Muting your rcvr is done separately.

Perry  W8au


On 2023-11-22 21:58, Richard Knoppow wrote:
> Old fashioned non-electronic TR switching, by which I mean the use of
> a mechanical relay and not a TR tube, generally have an extra set of
> contacts for muting the receiver. An example is the TR switch built
> into the Johnson Matchbox's. These have a heavy duty antenna relay
> operated by AC from the transmitter. Many transmitters had a switched
> AC output for running an external T-R relay. The relay in the Matchbox
> has a set of independent contacts for the receiver mute. Other antenna
> relays are similar. Most receivers (but not all) require a closed
> contact to receive. This may be on the B+ or a bias line for muting.
> In a few cases the receiver requires a closed contact for muting, for
> instance, the break-in relay in the Collins 51-J series. In that case
> a low voltage for the internal receiver relay can be had by putting a
> wall wort of the right voltage on the same AC line that activates the
> antenna relay. When the AC comes on switching the antenna from
> receiver to transmitter this supply activates the receiver break-in
> relay muting it.
>    However, most receivers have a muting arrangement that requires a
> closed contact to receive. It seems to me that requiring one to vary
> the gain controls on the receiver to transmit is extremely
> inconvenient.
>    In my original station, which was all home brew or modified
> surplus, I switched the mute connection on the receiver and also had a
> small relay right across the antenna terminals such that it shorted
> the terminals in "transmit". When on CW I could hear my own signals by
> putting the front panel switch in "receive", keeping the receiver from
> completely muting but the shorting relay kept the residual signal
> small enough so it would not overload the receiver. Worked very well.
>     A note: there is a device called a T-R switch that uses a vacuum
> tube. It is derived from a device used in radar. I am not sure I
> remember how they work well enough to explain it here but there is
> material on the web. I think the Barker and Williamson switch may be
> of this kind.
> 
> On 11/22/2023 6:28 PM, Rob Atkinson wrote:
>> I'm not familiar with the B&W switch.  T/R switching varies with
>> transmit power level.  If you are using a 100 w. transmitter and
>> receiver the Dow Key relay shoujld be fine.  Some vintage transmitters
>> have an AC connection on the back of the rig for a relay coil that
>> will power the relay when you transmit.  You don't have to have a
>> second set of contacts for muting.  Receivers mute in different ways.
>> I guess it's nice to have that but I have never had an automatic mute
>> switch here.  I just turn down the AF or RF gain on the receiver to an
>> acceptable level just before I transmit.
>> 
>> 73
>> 
>> Rob
>> K5UJ
>> 
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> SKCC 19998
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