[Spirit FM] mikereidis:
Yes, TI and Broadcom both have circuitry to allow Bluetooth and WiFi to share one 2.4 GHz antenna.

FM antenna is different: 76-108 MHz; Samsung has nice schematics that show a N and a P wire. I want to say separate for Tx and Rx, but I've gotten some conflicting info on that, based on some "info" I found.

I was going to say more about the info, but having considered that Broadcom might actually try to sue me for some stuff I have done and might do, I'm starting to think I shouldn't be so open about the "info" I've found and heard. Anyway, it's really not that interesting unless you are hardcore into this.

FM actually has 2 control paths and either can be used. The most common is via the HCI UART and thus potentially through Bluetooth. The 2nd is a dedicated FM I2C port that is rarely used. Dell Streak uses it, but my app can ignore it and go through HCI as usual.

I think there are some reasons why Tx and Rx might be on separate chip pins, but I'm not an RF expert and can't give anything close to an expert opinion.

One reason is to prevent software (even official software crashes) from transmitting. I suspect this makes FCC certification easier.

Maybe by "hardware" you mean the PCB and components, instead of the chip pins. IF the chip pins for a possible distinct FM TX function are grounded, then TX is impossible unless you modify the PCB.

Absolutely. Code get's re-used for many years, and IMO it's got nothing to do with "lazy developers".

Frankly, I don't understand why people are so quick to blame devs. They/We operate under commercial pressures; Managers are always pushing. That's what I've seen in over 90% of the 20+ SW companies I've worked for. Race to the bottom/globalization and all that.

The registers are pretty much known, if you know where to look. Some Tx code is in V4L drivers and some other obscure places. I don't think software is the problem. Assuming the software is understood (BIG assumption): Run the software, see no transmission and can't blame anything but the hardware or some mysterious reason.

That said, I've never tried to transmit with Broadcom hardware, only TI. I have 2 Broadcom phones, one with the cheaper 4325 (Rx only) and one with a 20780 (Not clear.)

I also have a Galaxy S with a 4329 but the S uses a Silicon Labs chip, and it appears no FM antenna connections run to the 4329.

So I'm leaving it to others to figure out if their phone does transmit. If any phones DID transmit, I suspect they would be the exception rather than the rule, and I can't afford to spend money buying all these phones and hoping... And anyway Transmit would IMO be a nasty pothole on the way to trying to improve my UI and support proprietary FM APIs... and I think it would only work on a few phones... And I think most people want their normal audio output to be sent to their FM receiver, and I'm not convinced that many phones would allow the needed audio routing.

So I still think FM Tx, if at all possible, might be a novelty confined to a few phones; Heck, sometimes Rx seems a novelty, there are SO many phones with FM/combo chips and no antenna connection, it saddens me (and en-richens the carriers). I've had HUGE numbers of requests for phones like the Atrix and even the new Galaxy Nexus and the prior Nexus S, and Rx just isn't possible (it seems.)

If I recall correctly, the Nokia N900 does FM transmit, but it's the doomed Meego. Nice phone, wish it was Android...

EDIT: Oh yeah, here's my post on that thread I linked where I point out a schematic showing FM_TXN and FM_TXP pins, as well as the RX counterparts: http://xdaforums.com/showpost.php?p=15415120&postcount=74