Built-in FM Transmitter?

[Lawnboy]

here is an interesting observation: this evening i had just finished building an fm transmitter and was trying to test it when i noticed something strange was happening with my radio. to make a long story short, i found that when i had a cable plugged into the line out jack on my (cheap) portable cd player, an area on the dial from 101.15 to 101.8 mhz went silent. around 101.6 mhz you can hear both the left and right channels very faintly through the radio. it only happens with the line out jack, and it will even occur with nothing plugged in if the player is within a few inches of the antenna. the silence drops off quickly beyond 101.8 and below 101.15 mhz. what is interesting is that it drowns out a fairly strong station even several feet away. i wonder what kind of circuit would cause it effect. has anyone else discovered anything like this?

[DrZarkov]

Yes, I've created a "pirate FM station" by accident when I was a 12 year old boy. (Of course I've made a real pirate station from that circuit). The transmitter was an Elco of 125 uF in an oscillating circuit with a coil of 30 windings around a small piece of wood. Power came from a 9 V battery, the sound input was a telephone microphone. It transmitted somewhere around 104 MHz, and you could receive it around several hundred meters in the neighbourhood. Actually it should not have worked, but it did.

BTW: The station "Antenne Atlantis" went offline after 2 days, when my father found out what I am doing...

[johnrpm]

Has anyone tried using an audio sender from a cd player, then from the receiver into a monitor, it would be a bit like broadcast tv, I think they use FM at 2.4g. I intend to try this but wondered if it would work OK.

[DrZarkov]

I've tried one of those now legal fm-transmitters with 50 uW. Result: Forget it! No recognizable picture. That 2,4 GHz transmitters are worth a try. The sound is transmitted somewhere in the UHF-area very close to the HAM 70 cm-band, 2,4 GHz is used for the picture. Unfortunally there are only 3 channels, our neighbour is using all three of them for his CCTV. I can receive all of them here...

[johnrpm]

I have tried a I-sender 2.4ghz audio sender, (no video) from maplins, it has
3.5mm jack cable to connect to the cd player or whatever into the transmitter and 3.5mm jack to phono for the reciever end, the units are rechargable from mains or usb, they claim up to 12 hours on a charge but have not tested this, the range is claimed to be 30 metres.
I charged the units and connected it up to my partly finished monitor, I am using peter smiths led amplifier and motor drive which works well with direct connection to the cd player, I did get a picture but it was lower quality and although the disc spun up to near the correct speed I had to manualy adjust it to get sync, so the result was not as good as I had hoped, but maybe with some though it could be improved upon.
It was strange to hear the disc spin up in the next room without me being present, similar to remote control.

P.S the audio was ok.