[SOLVED] need a stable FM transmitter for home use

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zsolt1

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hi,
I would need a small range & stable fm transmitter schematic . I search for something simple to build, with nowadays components that provides good quality transmission, specially of audio signals...

:grin:
 

hi,
I would need a small range & stable fm transmitter schematic . I search for something simple to build, with nowadays components that provides good quality transmission, specially of audio signals...
Click to expand...
Hi Zsolt
Well , you're looking for an FM transmitter . based on PLL ? or based on varactor ? or perhaps miller modulator ?
if you mention it i can send you a good circuit .
BTW ; what range of power ?
Best Wishes
Goldsmith
 

The odd thing about both those designs is the modulation level drops to zero at both ends of the tuning range! I'm suprised a better voltage/modulation arrangement wasn't used.

Brian.
 

If all you are after is FM audio, there's a lot of car stereo
FM modulators out there for cheaper than you can build.
Power levels are very low on the ones that use dry cells
and better on the ones that plug into the lighter.
 

hi,
the modulator can be any type (of course PLL would kick ass...), and low power RF amp,just for home use in short range.. max3606 would fit just fine my application, unfortunately it's not available at my electronic components provider so will have to look if it's reliable (speaking in terms of cash ) to order a pair of ic's from abroad ... meantime i'm still searching, starting with SMOVPO's website ;-) ... FM car modulator is a good option (and really cheep here...) but for now it's for plan B ............

zsolt
 

zsolt1 said:
hi,
I would need a small range & stable fm transmitter schematic . I search for something simple to build, with nowadays components that provides good quality transmission, specially of audio signals...

:grin:
Click to expand...

the difficult part about FM is not the modulation - this is easy to do with varactors and so many other VCO's available these days. The difficulty lies in ensuring that the carrier frequency stays stable & firm for short-term and long-term.

All of the small and simple circuits ignore this requirement, so your frequency will change all the time.
 


yes i agree , that is why i am asking for circuits that have been tried out before

- - - Updated - - -

what about this circuit:

has anyone saw it before?

PLL can be aded later
 

It isn't the schematic that causes the problem, it's the construction and choice of component materials. Even a simple single transistor oscillator will work fine under ideal conditions but might drift wildly as temperature changes or something moves nearby. The one you show in post #9 should be OK provided:

1. you stabilize the supply voltage
2. you DO use the extra amplifier stage, not for more power but to isolate the antenna from the oscillator.
3. you build the oscillator inside a screened box.
4. if you are picking it up on domestic VHF/FM receiver, you apply audio pre-emphasis.
5. you choose capacitors with suitable temperature properties to cancel thermal drift.

Ideally you use a PLL as this would make the circuit far more forgiving of component types.

Brian.
 

unfortunately not .... anyway i already have a solution, i use a AM transmitter from a long time ... it's just that i thought it would be nice to update with something new... meantime i'll give it a try with a car modulator next weekend ....... ...
 

kripacharya said:
The difficulty lies in ensuring that the carrier frequency stays stable & firm for short-term and long-term.

All of the small and simple circuits ignore this requirement, so your frequency will change all the time.
Click to expand...
Agreed, this is a problem with most cheap kits and simple circuits found on the net.

However, what I like about SM0VPO's circuits (aside from the very simplest) is that he puts some effort into addressing this very issue. So we see things like the oscillator being supplied by a voltage regulator (to avoid frequency drift as the battery voltage changes), and a separate power amp stage being used to isolate the oscillator from the detuning effects of the antenna.
 

godfreyl said:
what I like about SM0VPO's circuits (aside from the very simplest) is that he puts some effort into addressing this very issue.
Click to expand...

agreed. Harry's Homebrew Homepage's have been a source of inspiration & information for me for some time now.
 

@ Goldsmith
ok, send some circuits......... just for fun & pleasure for the eyes
Click to expand...
Hi Zsolt
sending some circuits . certainly . but with what method ? would you like that i send you an Fm transmitter via a PLL or perhaps a miller modulator or perhaps a varactor modulator ? which one exactly ? or perhaps you're interested in all of them ?
For instance this one is a miller effect FM transmitter which is good ! ( in fact it's out put will deliver both AM and FM modulations !! ) . take a look here please :



Best Wishes
Goldsmith
 

hi ,
plan B worked ! I got myself a fancy fm car modulator, i just need (to destroy it ;-) ) to increase it's range to ~50 m , i think a simple RF final stage will do...

.. so problem is solved

thanks to all for suport
 

hi sir i need a video and audio sender circuit diagram, most of the i got on line isn't working..i will be grateful if you can provide me with one here is my mail add get2kunle@yahoo.co.uk....thanks as you help me in this regard.....
 

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