[ARC5] Backwave

[Bill Cromwell]

Hi,

I went back to the original post from Rich, KB8TAD,  and reread it. The 
first time I read it I took it that the friend with whom he is working 
on the transmitter project was hearing the backwave at a distant 
location. The message is ambiguouis about that detail. QRM from the 
backwave has been discussed in the 'classic' literature and that is 
where my my mind went. Maybe Rich can clarify that. Other replies have 
been about the backwave in the adjacent receiver.

Dennis says the backwave is "exceeding weak" as transmitted but does not 
say weaker than... what. Later he says that the frequency shift cannot 
be heard at a local friend's home. Maybe he means the backwave cannot be 
heard there and *that* is encouraging. There is a significant population 
of hams who work the world with a few (single digit) milliwatts 
demonstrating that signals escaping from our transmitters *can* be heard 
at great distances and *can* cause QRM. If the backwave cannot be heard 
in the local neighborhood it probably cannot be heard, nor cause QRM to 
more distant hams. Dennis has apparently checked for that.

Thanks to Neil, ZL1ANM, for reviewing how those circuits worked 
originally. A couple of others pointed out those transmitters work fine 
"as designed". I have used keying relays in the past to key high 
voltages but that was in my home in the middle of the night and NOT in a 
B-17 at altitude! The mechanical clattering was unacceptable and I moved 
to blocked-grid keying. Any keying system has it's own caveats but 
mechanical noise is not an issue with blocked-grid keying. The relays 
are one of the reasons I have not had interest in using the transmitters 
with the receivers that I do use. Thanks to Dennis's comment about the 
keying transistor I will review that and maybe look for transmitters to 
"go with". Meanwhile I am happy with old ham transmitters with 
blocked-grid keying, including keyed oscillator and with one or two 
stages of isolation between the oscillator and the output stage.

I have a half dozen of the command receivers that I have been gradually 
'moving' back in the direction of "original" operation. If I live long 
enough they will be used with remote controls (probably home brewed) 
through the connector on the back. Maybe not museum pieces but as others 
have said..working "as designed". Meanwhile they are 'on the air' where 
radios belong. I do use mechanical relays with one switch for the T-R 
function but NOT for CW keying. Simple. Effective. Tolerable at 1 AM.

73,

Bill  KU8H


On 10/25/2015 11:16 PM, Dennis wrote:
> I run the osc in my T-22 continuously and key the PA cathodes via a transistor.  The back wave is fairly strong in the receiver but exceeding week as transmitted.  Key down the osc pulls down about 2 KHz.  Because I spot the rig key down into a dummy load, the osc runs 2 KHz above the transmitting/listening freq. so a decent IF filter or notch eliminates the potential self QRM.  On 80M the pull would be less (1 KHz?).  Osc and PA screens are regulated so minimal classical chirp.  One cannot hear the very fast 2 KHz pull in the home receiver or at a local friend's house.
>
> Dennis AE6C
>
>