Need help, fm transmitter

Thread Starter

Virtual

Joined Nov 25, 2018
6
Hi im new here so sorry if something is not up to the rules i just need a bit of help, im working on boosting the fm signal of my car fm transmitter x8(the ebay one ofc) and for the hell of it i cant find the antenna by poking around, i hope some of you will be able to help me couse ive tried using a radio far away and poking with a copper wire, and ive tried searching online but no help, thanks alot guys any help is welcome
IMG_20181125_115650.jpg IMG_20181125_115705.jpgIMG_20181125_115714.jpg IMG_20181125_115719.jpg
 
Last edited:

absf

Joined Dec 29, 2010
1,943
Isn't it obvious that the antenna is printed on the PCB on picture #3, on the bottom right (looks like square pulses waveform).

Allen
 
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Thread Starter

Virtual

Joined Nov 25, 2018
6
Isn't it obvious that the antenna is printed on the PCB on picture #3, on the bottom right (looks like square pulses waveform).

Allen
Yes but does no difference in range while addint a wire to it or even an full antenna
 

MisterBill2

Joined Jan 23, 2018
6,058
The device in the pictures is intended to transmit to a car radio from inside the car, a quite short distance. It is probably designed to NOT send a signal any farther. So how far do you want to send an adequate signal?? Please let us know. Adding an antenna to that device will not improve the results very much.
 

Wendy

Joined Mar 24, 2008
22,141
You could add a small inductor to make the antenna appear electronically longer by small I'm thinking 1μh, I have no clue what the value should be.
 

BR-549

Joined Sep 22, 2013
4,938
I am not real familiar with those units......but I would guess the squiggle ant. is for BT. And I would guess the FM TX is just an osc.......might not have ant. Or loosely coupled to a power lead. FM radios can be swamped with a local signal.

One might try coupling a wire to the FM osc........if you can find it.
 

MisterBill2

Joined Jan 23, 2018
6,058
The first question is does the thing even work at all? It could be that it does not transmit exactly on the indicated frequency, and with a digitally tuned car radio you will not hear it at all. So first, verify that it actually works sending to an analog tunable radio, such as a cheap clock radio. If it does work, you still need to tell us how much range increase you are seeking. The intended range of such a device is only a few feet to your car's FM antenna. It may be that the radio in your car has a problem.
So we need more information in order to provide a useful suggestion.
 

Thread Starter

Virtual

Joined Nov 25, 2018
6
Thanks for all the reply's, im looking to increase the transmitter to radio signal just by a few meters becoise it is just too weak, it loses signal any time there is anything on nearby frequencies, i would experiment with inductors or adding to the osc, but i cant find the bastard, my guess too is that the little printed antenna is for bt becouse that part works great,
Thanks again for all the reply's and effort
 

BR-549

Joined Sep 22, 2013
4,938
Have you got an SDR dongle. They can be found for 10 bucks or so. Great piece of equipment....and great radio. Check it out.
 

MisterBill2

Joined Jan 23, 2018
6,058
Thanks for all the reply's, im looking to increase the transmitter to radio signal just by a few meters becoise it is just too weak, it loses signal any time there is anything on nearby frequencies, i would experiment with inductors or adding to the osc, but i cant find the bastard, my guess too is that the little printed antenna is for bt becouse that part works great,
Thanks again for all the reply's and effort
That small section of trace that zig-zags , with nothing close to it, is the antenna. If this is for an installation in a car, and you only want to hear this device on the car radio, it could work to get another cable like the car radio antenna cable and route the end of the cable near the device. If it is not a car installation then it gets more complicated, but still possible. And the added advantage of not having to modify the thing.
Thanks for all the reply's, im looking to increase the transmitter to radio signal just by a few meters becoise it is just too weak, it loses signal any time there is anything on nearby frequencies, i would experiment with inductors or adding to the osc, but i cant find the bastard, my guess too is that the little printed antenna is for bt becouse that part works great,
Thanks again for all the reply's and effort
If this is for a car installation, an option is to use another cable like the car radio's antenna connection and run it up to the device. That would allow the radio to hear it much better. But if it is not for a car system it gets more complicated. AND it may also be that there is a problem with the antenna connection of your car's radio antenna.
 

Thread Starter

Virtual

Joined Nov 25, 2018
6
Car antenna is great, i van get foreign stations and im abou 150km from t je border, ill try connecting it like that as soon as i get home, tnaks alot guys u gave me great ideas
 

Audioguru

Joined Dec 20, 2007
11,249
The Micromitter was a project in Silicon Chip magazine then a kit was made. It used an FM stereo transmitter IC made by Rohm that is obsolete today. It used an attenuator at its radio output made with 3 resistors that are probably near the antenna on your circuit. Short or remove one or two attenuator resistors then your circuit will cause interference that will get you in trouble with the RF cops.
 

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MisterBill2

Joined Jan 23, 2018
6,058
The Micromitter was a project in Silicon Chip magazine then a kit was made. It used an FM stereo transmitter IC made by Rohm that is obsolete today. It used an attenuator at its radio output made with 3 resistors that are probably near the antenna on your circuit. Short or remove one or two attenuator resistors then your circuit will cause interference that will get you in trouble with the RF cops.
I do indeed see something in series with what may be an antenna, and if it is a resistor then possibly reducing the value can increase the range. But it is a very small part so measure it first, in case it vanishes.
 

Audioguru

Joined Dec 20, 2007
11,249
I see a zero ohms "resistor" (jumper) in series with the IC output to the antenna. There are solder pads on each side of the jumper with missing parts. The IC might have the attenuator inside it.
 

MisterBill2

Joined Jan 23, 2018
6,058
I see a zero ohms "resistor" (jumper) in series with the IC output to the antenna. There are solder pads on each side of the jumper with missing parts. The IC might have the attenuator inside it.
I was just thinking about the benefit of a resonant dipole antenna. Consider a series resonant connection to that IC with a parallel resonant secondary, coupled to a dipole about 27 inches each side, presuming that the frequency is in the middle of the US fm broadcast band.
 
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