[Hammarlund] HQ140X Receiver Muting & Standby

[Richard Knoppow]

    The HQ-140-X will act as a monitor when the Receive-Standby switch 
is left in Receive although its sensitivity may be too great. I used 
this technique for my Super-Pro by also putting a small relay across the 
antenna terminals, right at the receiver. This relay shorted the antenna 
when the main antenna relay was activated. Gave me enough to hear my own 
signal.
     I've done something like what you describe on an RCA AR-88, this 
has a stand-by switch which shuts off the entire B+ line. Bad because it 
causes the B+ to rise enough to stress the filter caps. I disabled it 
and use the AVC line to mute the receiver. Works fine.
    BTW, the schematic of the standby switch is confusing, helps to 
trace out what its actually doing.

On 12/5/2023 7:45 AM, Rodger Singley wrote:
> Ray,
> 
> In stock form, the terminals of the standby switch are in parallel with the relay socket.  With the switch in standby and nothing connected to the relay terminals, B+ is removed from the mixer, first IF, and AF preamp stages to silence the receiver for transmit.  For use with a transmitter, connect a normally closed set of relay contacts on the antenna relay so that the B+ connection is broken during transmit to silence the receiver.
> 
> I don't like switching B+ for standby and I modify receivers like this one to use the RF gain control bus for standby.  To do this, remove the B+ wiring from the relay socket and with an insulated jumper permanently connected between the leads that were connected to the two terminals of the relay jack.  Then install a 10K resistor between what is currently the grounded end of R40 and ground.  Connect a lead from the junction of R40 and the added resistor to one side of the relay jack and a jumper to ground from the other side of the relay jack.
> 
> You will still use a closed on receive contact from the antenna relay but now it will put the receiver into standby by biasing the receiver gain bus off instead of switching B+.  A variant on this technique is to use a 10K wirewound pot configured as a variable resistor in place of adding a fixed 10K resistor and this will provide a variable gain control during standby allowing the receiver to function at reduced gain as a CW keying monitor.  The Hallicrafters SX-88 and a few other receivers are already configured this way to act as a monitor during transmit.
> 
> Rodger WQ9E

-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998