Simple RF transmitter

[wmmullaney]

Hi all, I found this ~Antoon circuit and I wanted to know what does it transmit? If anything about what frequency would it be? How do you change it?


Thanks for any help...

**broken link removed**

 

[matk95]

the circut is an ocilator atached to an antener (i think) it sais in the text next to the image that by changing the capacitor/risitor you change the frequency

it could have things like an ldr ect on it to

 

[wmmullaney]

the circut is an ocilator atached to an antener (i think)

Yes it is, could I use a tuning capacitor in place of C1?

How would I go about hooking up an input?

 

[RadioRon]

The oscillator frequency is very dependent on the inductance of the coil, and yet no information is given about that coil so it is impossible to say what frequency this will operate on unless you design a coil yourself which is easy. This is a very poor transmitter and is only meant to demonstrate what can be done with very few components. It would be a terrible transmitter to add other functions to. If you want to build a voice transmitter, please look for a better circuit. Here is a good thread to look in :

https://www.electro-tech-online.com/threads/some-more-simple-fm-transmitters.12489/

If you want to build a really good one that operates at 88 to 108 MHz, use this, from Audioguru:

https://www.electro-tech-online.com/attachments/fm_transmitter_mod4_pic_schem_212-gif.7058/

 

[wmmullaney]

Ok, i'd still like to know what this transmits?


Can I use a tuning capacitor?

 

[wmmullaney]

Thanks for the links!

 

[stevez]

Some energy from this oscillator will radiate via the antenna and is likely to be heard as a hiss on a nearby receiver that is tuned to the fundamental frequency or on integral multiples.

You could use a tuning capacitor. When the oscillator is working it will likely drift and will be affected by proximity of nearby objects. Touch it or put your hand near it and it will detune. The signal will also likely be modulated by physical movements.

It might be a nice demonstration but I would not expect any kind of performance from such a circuit.

 

[nomadicbrew]

I think it is a purely basic RF Transmitter and you should Hear some kind of sounf from a nearby Sound receiver. Nothing much though.

 

[wmmullaney]

Some energy from this oscillator will radiate via the antenna and is likely to be heard as a hiss on a nearby receiver that is tuned to the fundamental frequency or on integral multiples.

You could use a tuning capacitor. When the oscillator is working it will likely drift and will be affected by proximity of nearby objects. Touch it or put your hand near it and it will detune. The signal will also likely be modulated by physical movements.

It might be a nice demonstration but I would not expect any kind of performance from such a circuit.

Thank You for answering!

I think it is a purely basic RF Transmitter and you should Hear some kind of sounf from a nearby Sound receiver. Nothing much though.

Would the signal be closer to the AM spectrum or the FM? Thanks Again!

 

[Nigel Goodwin]

It's a plain carrier, it's neither.

However, like pretty well all the circuits on that site, it's pretty crap!.

 

[wmmullaney]

Ok, so this could be picked up with AM radio? I wanted to use this with a simple AM radio as a tracking device(you push a button on the remote and the object with the radio beeps).

 

[mneary]

It probably won't transmit at one frequency; it's a non-resonant relaxation oscillator. My simulation shows that it puts out wideband garbage from about 1MHz to 100MHz. A lot of the crap fell at 11MHz and its harmonics; yours will be different depending on how you wind your coil, your battery voltage, and transistor.

 

[RadioRon]

It probably won't transmit at one frequency; it's a non-resonant relaxation oscillator. My simulation shows that it puts out wideband garbage from about 1MHz to 100MHz. A lot of the crap fell at 11MHz and its harmonics; yours will be different depending on how you wind your coil, your battery voltage, and transistor.

Actually, I am quite glad that you did this work as I was a bit puzzled at the configuration, but too lazy to analyze it further myself. It seemed that the capacitor was not involved in resonating the circuit, so there appeared to be no tank, just a feedback path. Your explanation hits the nail on the head, so thanks! It is possible that its spectrum is narrower than your sim suggests mainly due to parasitic and perhaps miller capacitances. If I had to guess where to start looking for energy, it would be higher than 20 MHz, and I'd use my spectrum analyzer set up for 0 to 300 MHz to start with so as not to miss it. I would think that the transistor runs out of gain in the high VHF region, wouldn't you?

 

[wmmullaney]

thanks all for the help!!