> Okay, now, can you explain to me how an FM transmitter, transmitting somewhere between 87 MHz and 108 MHz will interfere with your emergency services?
The fifth harmonic will land squarely in the chunk of band between about 435MHz and 500MHz, and being roughly 200kHz wide even assuming they're not overdeviating like hell it'll obliterate a huge chunk of the band. Given how poorly constructed many "pirate TXes are it's almost a given that they'll have ridiculous amounts of out-of-band radiation.
There's one very popular design available on the Internet which I won't link to but will leave as an exercise for the reader, which has a rather nasty sproggie that's only about 10dB down at around 156MHz when it's tuned for about 104MHz. Now, that chunk of the FM broadcast band is quiet around here, but the sproggie passes through the transmitter's largely untuned (at least, broad as a barn door) PA and out the antenna.
The whole thing is not terribly efficient at radiating something 200kHz wide all over the bottom end of the Marine VHF band, but it sure is noticeable.
I have measured some cheap aliexpross specials and they ware remarkably dirty.
A forest of spikes around the fundamental thanks to parts of the TX strip oscillating.
I guess the manufacturers just pulled every last bit of gain and output power from their transistors with minimal amounts of additional parts.
And the end result is something you cannot run even if you had a licensed FM broadcast band frequency.
The fifth harmonic will land squarely in the chunk of band between about 435MHz and 500MHz, and being roughly 200kHz wide even assuming they're not overdeviating like hell it'll obliterate a huge chunk of the band. Given how poorly constructed many "pirate TXes are it's almost a given that they'll have ridiculous amounts of out-of-band radiation.
There's one very popular design available on the Internet which I won't link to but will leave as an exercise for the reader, which has a rather nasty sproggie that's only about 10dB down at around 156MHz when it's tuned for about 104MHz. Now, that chunk of the FM broadcast band is quiet around here, but the sproggie passes through the transmitter's largely untuned (at least, broad as a barn door) PA and out the antenna.
The whole thing is not terribly efficient at radiating something 200kHz wide all over the bottom end of the Marine VHF band, but it sure is noticeable.
Source: literally my day job.