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Posts: 1
Joined: Thu Sep 05, 2019 5:57 pm

FM Radio to use Intercom antenna

Thu Sep 05, 2019 6:02 pm

This may not be possible but it would be great if the FM radio could utilise the Intercom antenna instead of finding headphones. This would make the phone even more useful to use in emergency situations, or when away without any headphones. Thank you! I love the BV9500 pro.
Posts: 27
Joined: Fri Feb 01, 2019 3:36 pm

Re: FM Radio to use Intercom antenna

Fri Sep 20, 2019 11:25 am

This is definitely possible but I cannot tell how. I'm thinking of my baofeng walkie talkie that uses the same antenna for fm radio. As a hardware solution you could try to solder a thin wire from antenna to one of the 3.5mm jack's pins (this you'll have to figure out). It's not an ellegant solution but maybe it will work. As for myself, I use a selfie stick with a wire (connected directly to the metal part) and a male 3.5mm jack. It's a pitty to have to use wire earphones for fm radio these days... I remember there was a nokia x2-02 that had fm radio without earphones! Like 7 years ago!?! Also it had fm transmitter inside :)
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Posts: 138
Joined: Sun Dec 02, 2018 4:53 am

Re: FM Radio to use Intercom antenna

Fri Sep 20, 2019 11:35 pm

That solution would work until direct RF from the UHF transmitter fries the FM chip's amplifiers (which is also your Bluetooth and WiFi chip). Even at only a few watts and even at four to five times the frequency, directly fed to the chip might be more than it can handle.

But then it might not. >shrugs< I wouldn't know.

Same time though, if you do go this route, you'll need to engineer a way to trigger the "headphones are plugged in" switch. I think this is a physical contact-break in the jack, but at the same time I've seen that some designs use an electronic signal to detect the impedance of the headphone speakers, microphone, etc. (especially on TRRS jacks such as are used in phones) to detect the difference between headphones, mic+headphones, or a selfie stick/camera remote shutter button.

It's possibly a bigger job than it would seem on the surface.

That Baofeng turns off the FM receiver when you hit the transmit button while listening, and there's an almost palpable delay between the receiver turning off and the transceiver keying up, then again when it switches back to FM receive. There's certainly a chip/relay that disconnects the FM receiver from the antenna during transmission.

I live in an area where radio signals are strong enough that just a short adapter (e.g. TRRS-to-TRS-headphone+TRS-mic splitter adapter) is enough antenna, and I carry one of those in my laptop bag for work. Small enough, light enough, etc. that if I listened to radio often enough I'd have no problem adding it to the numerous items I already carry in my pockets everywhere I go. Might work for you.

But I agree, the headphones-plugged-in requirement for an antenna is stupid.

(Edited for readability after editing to include a forgotten item)

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