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Reception of others' portable FM transmitters

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Reception of others' portable FM transmitters

Post by bmw » Tue Dec 24, 2019 4:09 pm

So yesterday I was driving down US-23, flipping through the stations, and I heard a dead carrier on 107.3 FM. Complete silence, quite strong signal, and then on my RDS, the following appeared:


Also heard a few brief flashes of music.

Upon google searching that, it APPEARS to be some kind of consumer-grade FM transmitter that apparently pairs via bluetooth to a bluetooth device and then re-transmits that signal over FM. I never knew that any such device existed that actually transmits RDS data of any kind (or for that matter, any that worked on bluetooth). At any rate, I assume the device wasn't made in the US as there's no way it was FCC-compliant. It was strongest when driving right past the Wal Mart in Tawas City (probably someone in the parking lot) but I got at least a faint signal between 1/4 and 1/2 mile away. It is of course gone today.

Anybody ever "DX" catch someone else's portable low-power FM transmitter while driving down the highway?

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Location: Fremont, Mich. / Seoul, Korea

Re: Reception of others' portable FM transmitters

Post by cckadlec » Wed Dec 25, 2019 12:20 pm

This is absolutely constant these days. I run into this at least every week and I live in a rural area. My own transmitter in my car takes music from my iPod and transmits it to the selected frequency (I use 87.7) with RDS and my device is 5 years old. The newer ones can transmit a good 1/2 mile and wipe out local and semi-local stations entirely in doing it. I had one girl listening to Taylor Swift that suddenly faded up over WIIL (a pretty strong signal locally) on my way home from work. She must have been about 10 car lengths behind me. Eventually, we both turned on the same country road and she was behind me and I was hearing her music solidly for miles and watching her sing along with it. I set my own transmitter on the same frequency playing Korn and watched her look all confused for a short time. Her transmitter even when she was a half-mile away was on seek with a massively strong signal on my car radio. Mine, in comparison, may extend with that strength out to a car behind me at a stoplight. I couldn't justify using that ridiculous sort of power in your own car to impede other people's radio listening.

I regularly struggle with this nonsense while doing my coastal bandscans. People leave these transmitters on with dead air 24/7 in their car and will do that for the entire day at the beach completely wiping out a whole frequency for me after I've travelled 10 hours to do a scan somewhere. I've been lucky that usually people leave before I do and I can "recover" the frequency, but not always. You're left wondering if a commercial or LP station is running dead air, or is it a transmitter? And you never find out for sure what you heard. It is also the cause of a lot of UNID stations where you just don't know if it was a fade up from a transmitter or a legit station. I was doing a bandscan in Northern Ontario last year and Indian music appeared just as I was hitting 101.5. Two Indian guys appeared a few minutes later and the music ceased just before. I questioned them about it and they confirmed it was their car transmitter. 101 frequencies and I hit that ONE at that specific moment. If I didn't see Indian guys, I would have marked that as a fade-up of an unknown Indian station and started looking unsuccessfully for matches and it would annoy me for a long time.

This stuff has been around for years and is a regular topic of conversation in nearly every forum or group. I'm surprised you're just now running into it. (Consider yourself lucky.)

[ Radio and weather geeks, beware! Coastal tropo studies, the 3-hr. Seoul AM Radio Listening Guide, 6-hr. 500 Top-of-Hour IDs, and Chinese FM at www.chriskadlec.comTuner: Grundig G8 • Location: Fremont, Mich. ]

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