The chip KT0915 of the other DSP radio project has a bonus frequency range well covering avionics frequency (around up to 140MHz) and it is curious how the Si4720 covers the frequency band. Here I checked it..

The first one is the lower limit of transmitting. As is written in data sheet, the lower limit is 76MHz (I am not sure the 400kHz offset).

And the next one is the upper limit of transmitting. Also as the same as lower limit, it is up to 108 as in datasheet. Off-band data can be sent to Si4720 but it simply cease to operate outside.

Next is the receiving lower limit measurement. It was 64MHz. The frequency data below 64MHz can be sent but it simply not receive any signal.

And the result of receiving. I indeed expect bonus extra upper limit but,,,,,

108 MHz

is the upper limit of reception. Not so interesting at all...

So the summary is

Hummmmm.....