More on AntiVox while SV is looking for the camera on his mobile phone..
The AntiVox, you have described Nigel is most certainly the way and the solution in the rigs that I do remember.. This is exacly the way they operate; the opposite phase to the mic comming via wire, to the phase comming through air from the speaker to the mic and the adjustable level to trim, and - importantly the Vox being the "governor", i.e. if you insist to "talk" - the transmitter does comes on..
Enclosed is a different approach and I have been confused by not remembering the "ropes".
In the Vox/Antivox solution (as per your description) - you are the person who makes the decision to make the transmitter to come ON. Quite right.
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Altrnative approach:
In the enclosed "solution" you do not have that choice, you either force it by pressing the PTT or you wait for the AntiVox to allow you to transmitt. The Antivox becomes the "governer" of the Vox.
There is an AC pickup from your Rx-audio being delivered to an OpAmp acting as full wave rectifier outputting DC levels only. Subsequently, the R1-C1 and C1-R2 circuits - do controll the rising and decaying slope and - resulting "envelope" of the RX'ed signal.
The distinction between a valid received transmission and noise is done using the comparator taking as it's 2nd input the DC level from a pot set just above the noise floor of the RX'ed audio(adjustable).
The rest is just pure "logic"
The OR gate does accept the Antivox decission or it is overriden by the PTT and - the NAND gate ensures that any side tone will disable the operation of the Antivox while you are already in the transmit mode listening just to the sidetone, meaning - your Tx is already On.
The "output" from the OR gate energises the digital "relay" and disconnects both mic and the keyer from the possibility to transmitt when the valid RX signal is pressent.
This idea was brought in the effort to provide a
fast "break-in" especially in the CW mode and the Vox can employ exactly the same "slope detection/shaping technique" to ensure a true hands free operation (unless your hand is keying in the CW mode ofcourse
).
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I do wish it was/is mine
The attached picture, represents only the logical flow of the signal and is not the exact diagram. In particular - the shaping of the receiving envelopes can probably be done better using an op amp; the R1, C1, R2 are only informative here to show paths for the capacitor C1 to charge and to discharge.
The main difference is, that the AntiVox controlls the operation and not the Vox.
Except for the "PTT override", the Vox controlls only when to quit the TX mode and the AntiVox gives the the Vox permission - when to begin it.
Being fast, it allows to break in between words/sentences (on SSB) and letters (on CW).
Regards,
xanadunow
PS. Sorry for the quality, it was all done in a hurry. The OR gate should really be the AND gate and the contact from the PTT override should really be shown as NC too .. do I need to redraw it? (engaging the PTT should prevent the gate from operating and deactivate the relay)
This idea is old and this is why I do not recall the original author.
Yes, the time delays of your TRX to go from one mode to another are longer and all you can do is to give it the "best shot"