FM transmitter (mod4)

[bananasiong]

Even mono, this transmitter is still working well and good quality!!

 

[fever]

thanks for the quick reply.
why i choose that BA1404 is bcz it uses less no. of components and the site has pcb layout(at which i always sucks).still i'll try BH1417.
and if u have any more stereo transmitter ideas pls let me know
thanks once again.

 

[bananasiong]

I have no idea about stereo transmitter, I've just finish a mono one.

I've made the field strength meter, the digital multimeter shows 40mV when it is very close to the transmitter, the further the lower.

 

[fever]

i already have mono transmitter.but for home theater system i need this stereo type.if any one has some simple design pls share.

 

[audioguru]

You don't want a simple cheap toy transmitter for a home theater system, do you?

 

[fever]

simple cheap toy transmitter for a home theater system

??? i don't get it

 

[audioguru]

You said you want a simple design. Cheap toy transmitters have a simple design.
1) Their RF frequency drifts if anything gets near it.
2) Their audio beats with the stereo 19kHz pilot frequency causing distortion and odd noises.

Make the Stereo Micromitter because it is good.

 

[bananasiong]

Hi,
Just want to make sure, this (mod4) FM transmitter, the input voice signal is amplified, its output to the oscillator is 180 degree out of phase from the mic input right? Then at the antenna part, another amplifier to amplify the modulated signal then invert the signal again to get back the same phase as the original signal? Or the phase doesn't matter?

Thanks

 

[Nigel Goodwin]

It doesn't matter!.

 

[audioguru]

Phase is important if you have more than one microphone or speaker. You want them all to have the same phase.

Inverting the radio signal does not change the phase of the audio modulation.

 

[bananasiong]

Okay, thanks!
My field strength meter shows only 40mV maximum, when the meter antenna is very near to the transmitter antenna. Both of the antenna are around 70cm long. But you told me that yours can up to a few hundred mV isn't it?

Thanks

 

[audioguru]

My signal strength was measured nearly 2 years ago. I think it was almost 10 times more than yours.

 

[bananasiong]

Wow. But I don't think there is any problem with my transmitter, maybe the meter?

 

[audioguru]

Didn't you add an emitter resistor to the output transistor to reduce its power?

 

[bananasiong]

Oh ya, I did. So this can reduce the transmission distance isn't it? I thought it is only reducing the power dissipated by the transistor.

 

[audioguru]

The emitter resistor reduces the voltage and the current for the output transistor. Power is voltage times current so the power output and heat are both reduced a lot.

 

[bananasiong]

Yes, I got it. Thanks

 

[MALLI]

i want to know the range of this mod4 transmitter

 

[MALLI]

please iwant design a fm transmitter with range above 5km please help me

 

[audioguru]

My Mod4 FM transmitter has a range of "across the street" to a cheap FM radio.
Its range is about 200m to my cheap Sony Walkman FM radio with its antenna attenuator set to "distant".
Its range is about 2km to my very sensitive home stereo and my very sensitive car radio with nothing in between.

10km range will need a very sensitive radio and enough output power to cause interference and is probably against the law without a licence. If you make it yourself then you won't be able to licence it.