What Type of Radio Setup Allows Simultaneous Receiving and Transmitting?

[Harold Rutila]

No -- I am not talking about simultaneously receiving and transmitting on the same radio.

I flew in a C182 a few months ago that had a GTN650 installed. While transmitting on COM1, we were simultaneously able to hear radio chatter (or the AWOS, etc.) on COM2. The same thing was possible when transmitting on COM2; we could hear whatever radio traffic was on COM1. In my experience, most airplanes completely block out other radio or intercom traffic when the push-to-talk key is activated.

I'd like to know more about why this is the case in the C182. Is this normal for every GTN650, or is a particular arrangement of transmitters and receivers required to make this happen? Can it be done with older radios?

 

[Sam D]

Wouldn't this be driven more by the audio panel than the radio?

 

[denverpilot]

Wouldn't this be driven more by the audio panel than the radio?

Yes.

It's possible to have as many receivers operational as you like, all routed to your headset (install ten if you like) and the PTT circuit and mic connected to one of them. (Technically you could also connect the PTT and mic to all ten, but there's little call for that.)

One of the difficulties in doing this all the time is what's colloquially known as "receiver de-sense". A nearby transmitter in frequency can overload a sensitive receiver to the point where reception on it is lost during the transmission. Quality of the front-end filters on the receiver, and physical location of the transmit and receive antennas (shielding the transmitter from the affected receiver) can be done in most cases with a reasonable (but for GA, completely unnecessary) amount of RF design work.

Example: AWACS and ELINT type aircraft are just LOADED with receivers and transmitters, all often on 3rd multiple frequency harmonics from each other. (3rd order harmonics still have quite a bit of energy at short distances and radios are spec'd to keep 3rd order emissions below a certain value... any transmitter exhibits harmonics...) and designing the RF "stuff" that goes on board and where the antennas are located on the aircraft body is a HUGE part of the design of such an aircraft, so the systems can be utilized simultaneously.

But anyway... long story short, yes... listening to two receivers while transmitting on one, is simply a function of the audio panel, and most audio panels can do it.