broad fm transmitter

Hi all first poster here, I am a crazy artist but am interested in getting into circuit building more. I have done a few robotics and radio kits, and received my ham license, never designed anything though.

I am interested in making an FM transmitter which would broadcast on the full 88-108 mhz range. I know that would be illegal to do in normal circumstances, but I am a bit of a survivalist nut, and I would like to know how to build something like that.

I have assembled a little 1watt fm modulator kit, but again no design involved. For my next project I would try to keep the same low power, but transmit a wider signal. Does anyone have experience building something similar?

Thanks for your time!

There are many FM transmiter kits. Start thare. Andy

FM radio stations have a fairly narrow bandwidth and the same with FM radios. If you make an FM transmitter that modulates its frequency from 88MHz to 108MHz then you will need to design and make a radio with a very wide bandwidth to receive it. If you receive it on an ordinary narrow-band FM radio then it will be extremely distorted and nobody will understand anything you say.

Survivalist Nut? Why will anybody hear your transmitter on their FM radio? Unlike AM, an FM radio has a "capture ratio". If it receives two transmitters that are both on the same frequency then it plays only the stongest one and ignors the weak one. That is why AM is used for airplane communications to allow another transmitter in the same frequency to break-in and be heard.
But I don't think your transmitter will have more power than a high power radio station so it will not break-in and will not be heard.

Interesting to note about the AM radio aspects...However my radio station may overpower other stations if I happen to be much closer to the receiving radio. It is also possible (at least hypothetically) that most other radio stations would be shut down in some sort of nationwide emergency.

Now I get what you are saying about a broad signal needing a broad receiver, but what if you were simultaneously transmitting on each station (88.1, 88.3, 88.5...108.9)? Would it be possible to send and receive such a signal? Would that be a very complex circuit?

Another option would be to have a computer driven circuit and have a signal that cycles quickly through each frequency so quickly that you could not tell it was doing it. Any thoughts?

Whatever the case may be, I'd like to hypothetically assume I could build this to be mobile, ideally fitting in a bag or backpack, or operated by a 12V car system.

Thanks for the feedback!

audioguru said:

If it receives two transmitters that are both on the same frequency then it plays only the stongest one and ignors the weak one.

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I get two equally strong stations on the same spot, but the radio plays single station when the areal turned to the corresponding directions where one signal dominate the other in terms of strength.

wiznas, I know there's commercial fm transmitters available cheaply that can transmit signals anywhere on the FM band allowing around 200 selectable stereo channels. It is cheap too. It can be a modified circuit using a Chinese version of BH1417.

wiznas said:

I am interested in making an FM transmitter which would broadcast on the full 88-108 mhz range. I know that would be illegal to do in normal circumstances, but I am a bit of a survivalist nut, and I would like to know how to build something like that.

Click to expand...

OK, I'll bite. What does survival have to do with being able to broadcast on all FM channels simultaneously?

This is a 'band jammer' I think, not even just a channel jammer