Electronics > RF, Microwave, Ham Radio

full duplex SSB with the two parties on opposite sidebands?

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cdev:
Does anybody think that would be possible?

You would need to use a directional coupler of some kind to isolate the receiving and transmitting signals, also they would need to be really clean! Also you would need very low SWR.

ivaylo:
Sure, this beast used to be able to do it

Richard Head:
Been done years ago. For some reason never caught on.

vk3yedotcom:
It's a bit of a novelty and both stations would need to be set up correctly with very clean transmitters and high dynamic range receivers.

Another approach to full duplex I've heard work here in VK3 involves a remote receiver, one station transmitting AM and a VHF link. 

Station A (the crossband controller) transmits an AM signal on 3.6 MHz.  He has a remote AM receiver about 50km away. Its audio is transmitted via a UHF link to Station A's home location.  Audio from this link goes into a mixing box and fed to the 3.6 MHz AM transmitter (along with audio from the microphone of Station A). This audio is also transmitted on a local VHF frequency.

Station B transmits LSB on 3.6 MHz.  His signal is picked up by the remote AM receiver and transmitted to Station A via his UHF link.  Even though it's only an AM receiver, the carrier from Station A forms a BFO so that the signal as heard by Station A is resolved correctly even though the remote AM receiver does not receive SSB by itself (without the carrier from Station A).  The transmission from Station B is retransmitted by Station A on Station B's frequency as well as on the local VHF frequency.  Station B doesn't have to listen to that local VHF frequency but if he does he can enjoy full duplex communication with Station A and also hears his signal come back. 

Potentially Station C could be transmitting USB on 3.6 MHz and be retransmitted by Station A so it could be a 3-way full duplex (triplex?) crossband.  I haven't heard this but can't see why it wouldn't work.

voltz:
If you're talking true full duplex TX RX on either sideband, then my main concern would be front end swamping or even component break down. The more you can attenuate the TX at the RX section during transmit the better. You'd also need a very selective receiver.

1) using some kind of super narrow notch filter tuned to the TX frequency in the RX path.
2) using a 3 port circulator arrangement allowing both TX and RX to be connected simultaneously to one antenna.
3) internet connected remote TX or RX station in another location.

If its not full duplex but more like a break in system, (listen only during the TX gaps) then RF pin diodes could be used to block the RX during TX speech. Better than VOX, where is actives during the speech envelope and has no delay.

Well there's some ideas, but yes, pretty sure its possible one way or another...

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