I see a lot of these small transmitters that plug into the cig' lighter for power and accept USB and Bluetooth as a source for music to re-transmit to your car radio via FM.
Easy to find dozens on Amazon and other sites, but one spec that I don't see on any of them is how much power they transmit with ? Can I use one in the house and transmit to all the FM radios in the house ? I am looking for an effective radius ?
Any help is appreciated. Thanks
Not very far, if the one on our Subaru is anything to go by. On a recent trip in the countryside (no local interference) we had to revert to a wired connection to continue listening to the audiobook we had on. Obviously on the highway there's a limit tolerance for fiddling with radio tuning etc, so it might have just drifted outside the AFT range of the FM channel we were on, but still, that's something to think about.
If you wanted one for your house, I'd look for a device sold for that purpose, and failing that I'd open it to attach a better antenna.
CH
On a sunny day (Sun, 23 Jan 2022 07:47:11 -0800 (PST)) it happened Sid 03 snipped-for-privacy@gmail.com wrote in snipped-for-privacy@googlegroups.com:
No idea
I have one. works perfectly on the same floor to a big FM radio, not tried in other places in the house, plays mp3 music from SDcard. Payed about 9$ for it on ebay.
Your neighbors may receive the transmissions too, copyright?
I think you'll find the answer varies, and is very unlikely to be well specified. Clifford gave you a case where he had trouble within a car. I on the other hand have experience listening happily to the transmitter in another car when we were travelling together - mostly reasonably closely, but certainly not bumper-to-bumper. I think there would be no problem picking up the signal throughout the house when that car was parked outside.
Or you can make your own:
Nice links: When I get some time I will order one of the kits. Thank you.
The answer is actually very well specified, but many devices ignore the standard. The maximum effective radiated power in the UK and the EU is 50 nanoWatts when measured under specified conditions which include ferrite absorbers at regular intervals on the power cable. This means that without such ferrites, as for example in a car, the power radiated will be significantly higher than 50nW because of radiation from the wiring harness. This is just as well, because a genuine 50nW signal only gives a decent signal to noise ratio at a range of up to a few metres. I designed such a product a long time ago and was present in the test lab when the measurements were made.
John
I meant "not specified" in terms of documentation on the devices - as you say, not all devices will follow the rules and standards. But it is interesting to know what the standard says, even if it is ignored in practice!
Jan, looking at all those projects from the link(s) that you posted, most talk about minimum frequency drift. I thought that crystal controlled radios did not experience frequency drift, or at least negligible drift ?
Thanks
On a sunny day (Mon, 7 Feb 2022 19:41:57 -0800 (PST)) it happened Sid 03 snipped-for-privacy@gmail.com wrote in snipped-for-privacy@googlegroups.com:
Yes crystal controlled, in this case phase locked loop should have negligible frequency drift for an _FM_ modulated radio transmitter,
As long as the loop is locked that is.
But if you have a 2.4 GHz transmitter locked to a 10 MHz crystal then the 10 MHz is multiplied by 2400 / 10 = 240, and so is its error.
If the 10 MHz now drifts 10 Hz (1 part per million, so 1 ppm) then the 2.4 GHz will drift 2400 Hz. If the modulation type was SSB then a 2400 Hz shift will be totally out of audio range! So a solution in a case like that (QO100 ham satellite) is to lock the 10 MHz crystal to for example a 10 MHz Rubidium frequency source that has a much lower drift than 10 Hz. Or use some other precision 10 MHz source.
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