HF Radios tuned to same frequency cause damage?

[jetfuelonly]

Trying to determine if this is true:

Tuning both HF radios to the same frequency could cause damage to the non-transmitting radio while the other transmits. This is slightly confirmed on the following webforum, but it is not specifically related to aircraft and may assume two antennas when I understand most aircraft have only one HF antenna.

Two HF Transceivers --- do I need to take precautions ? [Archive] - QRZ Forums (http://forums.qrz.com/archive/index.php/t-354947.html)

I would hate to damage expensive radios, but it's the first time I've heard this and if it's true we should keep educating each other on it.

[grounded27]

I had heard the same but never confirmed.

[HEATHROW DIRECTOR]

The receivers should be equipped with a muting function to "switch off" when a transmitter is being used in close proximity. I employed such as system when I had separate receivers and transmitters in my amateur radio station 30 years ago so I am sure that modern technology must have thought of something similar.

[aveng]

Most modern jets have 2 HF sets feeding one antenna - so when the key line for one HF is activated (mic keyed) there is a relay that electrically disconnects the other receiver.

[henry_crun]

Wiithout going into specific receiver designs, you are right to be cautious. The receiver first amplifier stage will receive the full blast of the transmitter signal and the filtering at that stage is only rudimentary so any close frequency (on the same band) could well be a concern. The only safe way is to simultaneously open the aerial connection and ground the receiver input. Be careful with screening and grounding arrangements.

Individual receiver designs may have electronic protection if they are intended to operate near to transmitters, but you would need to look at the schematics and specifications to verify.

[Wodrick]

Aveng has it.in most modern HF systems, using the term generously, using one antenna HF interlock prevents simultaneous transmission and grounds the input to the unused one.
This was usually the case with dual antennas too, although right now I can only think of one, the early 747s had a seperate HF antenna on each wing tip, so reasonable physical separation.
They depended on fit some had interlock some didn't.

[Badwolf960]

Hello, I do product line engineering support for airborne HF radios and the previous posters have it correct. It will depend on the exact equipment type and installation but the desired state is the have the "off-side" radio off the antenna when the "on-side" radio transmits. This would be advised even for dual systems with separate antennas unless the installation accounts for proper antenna isolation. Some equipment support simultaneous operations (SIMOPS), however, these tend to be military high power rigs.
I'll disagree politely on the "modern" as these radios are now software defined and use is much easier if Automatic Linking Establishment is used. It's a whole lot cheaper to use than that expensive satellite time! :>

[Andy_P]

Does not matter if they are tuned to the same frequency or not. The receiving radio will get the full signal regardless of the frequency its tuned too.

Receiver should be disconnected whilst transmitting on the other set.