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I noticed that on some higher-end transceivers, the panadapter/waterwall is still being displayed during transmission. How is this possible? If the panadapter is part of the receiver, it should be disconnected from the antenna during transmission and if it was using some sort of directional coupler or tap it would lose way to much signal to be of any use.

Is there some special circuitry at play here or is it only a display trick?

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I don't know what the specific devices you're referring to do, but a couple of things are all technically possible without great effort:

  1. the ADC that is used to calculate the waterfall in receive-only mode is still connected to the antenna, maybe with additional physical attenuation (which you could trivially reverse in digital domain by multiplication with a constant, the only thing you trade is sensitivity)
  2. it displays the transmit spectrum, which is inherently known to the digital logic, anyways, since it defines the transmit signal
  3. A combination of the above
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    $\begingroup$ After checking again, I found a video of the IC-7300 where we can see that during transmission the rest of the spectrum disappear youtu.be/jzRNFcEOrvU?t=126. It looks like it is solution #2. $\endgroup$ – ITChap Oct 5 '20 at 14:31
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  1. The radio has multiple antenna ports and full-duplex capability, and the operator has selected different antennas for transmit and receive. Or,

  2. The radio just displays the transmit spectrum on the waterfall, and it isn't coming from the antenna at all.

I've used radios with both of those options, so they're both definite possibilities.

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I havent looked into the mechanics too deep, but FlexRadio has a full-duplex feature for those models with 2 SCUs (spectral capture units) in the radio.

Each SCU goes off to a different antenna, and as long as antenna separation and monitoring (or precalculating) dbm levels happens, it works well.

I dont believe however you can do full duplex on the same band for obvious reasons.

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