Modify FM Transmitter

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danuke

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I have an FM transmitter that I bought a number of years ago that transmits on FM freq. from 88MHz to 108MHz. I was wondering if there is any way to modify it so that it will reach a little further. Right now it transmits to about 10-15 feet. I would like to modify it to transmit to about 25-30 feet. Is there an easy way to modify it so that it will have a gain in the output power? It runs on a single AA battery.

Thanks,
Joe
 
Try Audioguru's modded ver4 of FM Tx. it is ofcourse handwired on bredboard and well stablized (optimized).
 
My transmitter has a range of more than 2km across a wide river valley to a very sensitive FM home stereo or very sensitive FM car radio. Its range is about 300m to my Sony Walkman FM radio.

It uses a 9V battery that produces 36 times more power than a 1.5V battery.
Its antenna is 80cm long.
It has an RF amplifier transistor feeding its antenna.

I used it for only about 1 hour because it is illegal.
 
can I get your transmitter circuit please ??


may I have the curcuit which you talked about please ?
be sure that Iam not gonna use it in a bad fields...so can I ??!
 
Joe - I'll make the assumption that your circuit is compliant with all the rules and regulations that apply to your location.

A. Try changing the orientation of your antenna. Not sure what you are using.

B. Add an ammeter (probably milliamps is what you need to see) in series with the FM transmitter so you can see how much power is taken from the battery. With all other things left the same - tinker with the antenna to get the current to increase. The ammeter will show an increase in power in - as a result of better power transfer (maybe) to the antenna - with a possible increase in output power.
 
You haven't described the antenna, so I assume it is a piece of wire coming from the unit, or perhaps a simple telescoping rod antenna. Your desire to double your range to 30 feet is refreshingly modest. Most people want to improve range from 10 feet to 3 miles! I think you can improve things a lot by making your antenna longer or higher or both. You may find that certain lengths are better than others and longer isn't necessarily better, but to find those lengths you may have to experiment, the old cut-and-try method. Others have found that these lengths are often very good (+/- 25% or so): 1.25m or 0.63m.
 
A guy on another website souped-up my FM transmitter and got much more range out of it. I didn't try it because the range of mine is far enough.
It is mono, not stereo but it sounds great.
 

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  • FM transmitter pic + schem.PNG
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I'm not after trying to broadcast a radio station -- no need to... But I'm just looking to be able to have it transmit and reach across the house a room or two.

The antenna is a telescoping antenna that when fully extended, swivels 360 degrees.

Thanks for all the input. It's given me some ideas to try to see if I can improve the range a bit.

Thanks,
Joe
 
You forgot to post the schematic of your FM transmitter for us to recommend a mod that will increase its range.
You also forgot to say if your receiving radio is a cheap one with poor sensitivity.
 
audioguru said:
You forgot to post the schematic of your FM transmitter for us to recommend a mod that will increase its range.
You also forgot to say if your receiving radio is a cheap one with poor sensitivity.
Click to expand...

It's a store bought transmitter so I don't have a schematic for it. I wish I did though. Here is the same transmitter model and everything https://www.amazon.com/Arkon-SF120-SoundFeeder-Wireless-Transmitter/dp/B00006JPBS


The receiving radio I'll be using most is a moderate receiver. It's part of a portable mp3 player/radio combo made by SanDisk.
 
You have a very cheap FM transmitter and a very cheap receiver. 10 feet (3m) range is pretty good.
 
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