a question about fm radio

[mister_ed]

hello again ..to all i have a question if it is possible to do something with a fm receiver(you know the kind we can buy at cheap shop less than a 1$ ..is it possible to convert it to transmit in same freq range instead of receiving.my question might seem stupid to peoples but i want to know and how..

mister_ed

 

[Swanepoel]

Sorry it's impossible to convert a FM receiver into a FM transmitter.
The transmitter needs a modulator and your receiver has the opposite (demodulator)
I built a small FM transmitter from a site onec that had a range of about 50m and it cost me about (R20.00 | 1.5pounds | $3) so you can build one for around the same price as that elcheapo receivers.

 

[Andy1845c]

I don't think so.

Check out this thread.


Then scroll down to AudioGuru's reply. Try his circuit for a low power FM transmitter. I havn't made it, but others say it works good!

 

[Nigel Goodwin]

I don't think so.

Check out this thread.


Then scroll down to AudioGuru's reply. Try his circuit for a low power FM transmitter. I havn't made it, but others say it works good!

But what's that got to do with converting a $1 FM receiver?.

 

[mister_ed]

ok i posted before about i want make a r/c car maybe optic one but i got another idea i want used a 1$ radio fm one for the receiver and i need help for the transmitter.. i just need 1 fonction to do for my car now activate counter clockwise(motor) only for the reverse ..i hope you follow me my idea was used a fm radio (1$) for the receiver is possible? second what is the simplyest trasmitter i can do for just the function i explained.


thanks in advance!

mister_ed

 

[Hero999]

But what's that got to do with converting a $1 FM receiver?.

I think he ment you can build a transmitter for the same price that transmits on the same frequency.

 

[Swanepoel]

I suppose if you want to use the FM Radio Receiver you can hook up a filter at the receiver output that allows only a certain frequency or frequencies above a certain level to pass (high pass or band pass filters).
Then connect the filter output to a transistor / FET to drive the motor.
At the transmitter end you'l have to generate a frequency that will pass through your filters and send that is an input to your receiver.
As you can see this will be very hard to achieve and will cost alot.
Building RF circuits is not that easy.
If you want to stick to low cost RF try AM transmitters and receivers, they are much easier to build and cost less.

link for a basic FM Transmitter (if you still want to stick to FM)
https://www.aaroncake.net/circuits/fmtrans.asp

 

[Swanepoel]

A few links for AM transmitters and receivers

https://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html

https://www.antiqueradio.org/transmitter.htm

 

[Andy1845c]

I posted at the same time as Swanepoel.

I ment - No, I don't think you can do that with an FM radio.
Just thought I would suggest AG's transmitter if its is somthing he wants to try and build.

 

[audioguru]

I simulated the preamp transistor in the "garbage" FM transmitter. It is severely distorted with a typical 2N3904 transistor and is worse if the transistor has a high gain. The radio part of the transmitter will drift its frequency all over the place.

 

[enahmadbs]

I don't think so.

 

[audioguru]

The preamp transistor in Aaron Cake's FM transmitter is also severely distorted.
The preamp transistors are not biased properly.

 

[Leftyretro]

I bet Mcgiver could have done it

 

[Hero999]

I agree with audioguru, that simple transistor amplifier is crap!

 

[Sceadwian]

Couldn't you add negative feedback by adding some emitter resistance?

 

[audioguru]

I added an emitter resistor and the gain became reduced and the distortion also became reduced.
Then I bypassed the emitter resistor with a capacitor to eliminate AC negative feedback but keep DC negative feedback but since the transistor is incorrectly biased it still is very distorted.