Cool hack, BLIZZARD; I'm definitely gonna have to try this out.

Unfortunately, that's a bit more complicated than it sounds...

First, it's not currently possible to use FM receiver and FM transmitter at the same time. There's probably a direct interlock, but there's also the fact that fmrx requires headphones (for an antenna), and fmtx won't run with headphones (presumably to avoid them functioning as an antenna and exceeding field strength limits). This stuff may be software-overridable (at your own risk of FCC wrath) but there's more...

Second, if you get RX on while transmitting, the recieved signal is likely to be too strong -- probably won't destroy anything, but it will overload the receiver and you will get garbage, on frequency and for any nearby frequencies (depending on the tuning filter, but FM tuning filters are generally not very high Q, because the capture effect eliminates the need for it).

Third, even if you get FM tx and clean rx in the same device, it will always hear itself strongly (because it's no more than 4" away) even when there's significant interference at your vehicle's antenna (10x as far away = 0.01x field strength), and because of the FM capture effect, it will be difficult to impossible to establish a meaningful interference measurement for those conditions.

So basically, you have to stop transmitting for a moment to check interference strength, which could plausibly be done between songs (assuming no interference). Then, if you do have interference, you'll again need to shut down the output to scan for a new channel, power the tx back up, and use RDS to hop the radio onto the new channel. Meanwhile, since there is interference, and you've just disabled the fmtx, the receiver will be picking up the interfering station for some seconds, before it eventually comes back on and switches channel.

To me, that sounds highly disruptive as a listener, and I'd much rather have the same stop/scan/restart/hop happen by user command -- e.g. a desktop widget to do all that -- when I want it to happen. So I think the logical extension of this is to do:

• pause music (if playing)
• stop fmtx
• scan channels (as is done now)
• start fmtx
• use rds to hop to the new frequency
• resume music (if it was playing)

IMO, unless the issues with antennas can be worked around, it may be best to also enhance headphoned so that if phones (or better a dedicated antenna cable with a specific resistance to emulate, e.g. AV cable, in order to preserve the stock FMtx off function when real earphones are plugged...) are plugged while FMtx is on, it triggers the channel-finder, then (when cables are removed) things proceed to the new channel.

I'll have to look into this some more; as you can probably tell, I'm writing this from the top of my head with no research, so please take nothing in here as definitive.