I think you can rewire the antenna switching to eliminate one set of contacts.
RX common port: ANT on RX, GND on TX
TX common port: dummy load on RX, ANT on TX
(Slaps palm on forehead.)
Of course! Many thanks, that's much better. Revised schematic:
I'll get going on building this one soon, should be able to find all of the parts at my local electronic components store.
Martin: I'm very surprised at the various responses. Seems that nobody recalls the "good old days" when the RX/TX was done with a simple relay and switch.
The relay was between the transmitter, receiver and antenna. Switch activated: Relay pulls in and switches the antenna to the transmitter. Switch deactivated: Relay drops out and signal goes from antenna to the receiver.
When the switch is activated for TX, the RF gain control on the receiver is backed off and the CW tone is monitored with the receiver.
That wasn't practical with my set because it gets overloaded -- you cannot get tone, even with the antenna input shorted (it's a regenerative set and doesn't have an RF gain control). Hence, the existence of a sidetone oscillator inside the transmitter -- this was in the original ARRL design, which makes it rather sophisticated for a total beginner's Novice project! In the original ARRL setup, the receiver's headphone output is wired in parallel with the transmitter's sidetone oscillator. Thus, all you have to do is provide a knife switch at the antenna (to switch between receiver and transmitter). Changeover between RX and TX required two maneuvers: change over the knife switch; and turn down the AF gain to zero to avoid getting your ears blasted by an overloaded signal from the RX (if you leave the AF gain above zero, the carrier signal white noise blanks out the sidetone that's fed from the transmitter).
Then, I made things more complicated for myself by adding an extra AF stage, and a speaker, to my receiver. In order to monitor the sidetone on the speaker, it was necessary to feed it from the transmitter's sidetone oscillator to the input of the final AF stage in the receiver. In order for the AF gain control to continue working properly both with the headphones and the speaker, while still "muting" the overloaded signal on transmit, I came up with the above-described proposal for a (now three-pole) TR switch and relay. It will have the additional advantage that T/R switching will now require only a single maneuver: flicking the switch (no need to back off the AF gain any more).
It's a case of getting hoist with my own petard. The only reason I added the speaker was for casual band monitoring, and also to "show off" my station to visitors without their having to wear headphones. But actually operating my station with the speaker switched on requires this rather more complex T/R setup. I think it will be fun anyway, and in the end slightly more efficient than the original ARRL setup: a single maneuver for T/R, plus easy "zero beating" of the receiver with the transmitter.
No one has answered my question about positioning: logically (from an electronics point of view) this switch goes on the extreme right of my desk, near the telegraph key (this enables a simple left-to-right cabling at the back of the desk). But this would mean that the right hand is doing three things: keying, switching over, and writing down the incoming code. Meanwhile the left hand only has a single task: operating the receiver. Is this a bad idea?
Yes I know, these are picayune details. I'm trying to occupy my ham radio time usefully while my next-door neighbors ponder my antenna proposal: finalizing the T/R setup will help me get on the air quickly once those negotiations are completed.
73 de Martin, KB1WSY