Basic FM transmitter

[audioguru]

@audioguru,

this is just a basic transmitter so u can't use a powersupply to power this circuit! recharge the battery if it is low will be good!

No.
Of course the FM transmitter can be powered from a power supply but then it will not be portable.

 

[carbonzit]

bcz it will generate hum and distortions when use powersupply or u might need a very well filtered (smooth) powersupply

What? Where do you get that from? Any power supply with a capacitor filter would work as well as a battery with this circuit.

 

[audioguru]

Maybe power supplies in his country do not have a filter capacitor.

 

[colin55]

This is entirely untrue.

What? Where do you get that from? Any power supply with a capacitor filter would work as well as a battery with this circuit.

A lot of the other comments are entirely untrue. The circuit you posted was drawn by me and works very well. I have sold over 30,000 kits using this type of circuit and the output is absolutely perfect. You cannot tell the difference between someone talking in another room and the reception from an FM radio.
It would be better for you to build the circuit before you make any comments, as it is obvious most of the posters know absolutely nothing about FM transmission. I wrote 5 books on FM bugs and sold over 100,000 kits of different types.
The stability is phenomenal and the range has been over 27 miles from a 3v, 15mW bug left on top of a mountain as reported by a customer.
The bug does not “splatter all over the band” - firstly because it does not have the power and secondly the output transistor is not over-driven.
See Talking Electronics site for a full description of how these circuits work – most of the circuits have never been explained before and I can understand why very few know how they work.

 

[Ziddik]

any "Holy" filter capacitor can't solve the hum on this circuit as its directly connected to powersupply! It will NEVER stable using powersupplies! Maybe u might need 100s of capacitors to filter the supply well.. Looks like audioguru never made a fm transmitter because he doesn't make any sense, he still doesn't knw it

 

[Ziddik]

like collin said most of u must try to build an fm transmitter before posting this useless comments

 

[alec_t]

re post #24

the output is absolutely perfect

When the RF waveform is so different from a pure sine-wave it isn't perfect! Because of the distortion (it looks as though the transistor is clipping the wave) the output waveform will contain lots of harmonics of the fundamental oscillation frequency and hence WILL cause interference across a wide frequency range.

 

[alec_t]

Maybe u might need 100s of capacitors in series to filter the supply well.. Looks like audioguru never made a fm transmitter because he doesn't make any sense

I think it would make better sense if the caps were in parallel, Ziddik!

 

[audioguru]

The circuit you posted was drawn by me and works very well. I have sold over 30,000 kits using this type of circuit and the output is absolutely perfect. You cannot tell the difference between someone talking in another room and the reception from an FM radio.

Deaf people like you cannot tell the difference between your transmitter that is missing pre-emphasis (treble frequencies boost) and live music or speech that goes up to 15kHz. The de-emphasis in all FM radios cuts the treble boost back down to normal and cuts hiss. But your transmitters sound muffled on an FM radio.
My FM transmitter has pre-emphasis so it sounds perfect to a person with normal hearing.

 

[audioguru]

"Looks like audioguru never made a fm transmitter because he doesn't make any sense"
Where did this quote come from?
My FM transmitter fixed many problems with an FM transmitter that did not work. It is fairly cheap and simple but it works and sounds very good. I explained its good points.

 

[carbonzit]

any "Holy" filter capacitor can't solve the hum on this circuit as its directly connected to powersupply! It will NEVER stable using powersupplies! Maybe u might need 100s of capacitors to filter the supply well..

This is just more ignorant tripe from our Indian friend here. Hundreds of capacitors??!? Obviously you know nothing about how to calculate power-supply ripple.

 

[Ziddik]

This is just more ignorant tripe from our Indian friend here. Hundreds of capacitors??!? Obviously you know nothing about how to calculate power-supply ripple.

that means u dont accept the truth as i am an indian? Have u ever made an fm transmitter? Try to make one before posting useless and ignorant comments! its gud than babbling like a little kid who knows nothing.. Its definitely true u cant power this type of circuits using a powersupply!..
And stop posting ignorant and racial replies!

 

[audioguru]

Here is the assembly manual for an excellent Ramsey FM stereo transmitter kit. It uses a modern IC with a frequency synthesizer, quartz crystal oscillator and phase locked loop for a rock solid RF frequency. It can be powered from a simple wall-wart AC-DC adapter.

The instructions talk about the law in the USA about not causing interference to a licenced radio station's listeners.

 

[carbonzit]

cz,
Look at the .IC [ initial condition] on the base of the 1st transistor.
If you start from zero V, the 4.7uF cap takes ages to charge up via the 100K, so the transistor is not biassed on until the Vb reaches ~0.65V.

Aha! That's what your ".IC" is for--you're setting initial conditions.

To see the 'RF' you must select a time interval shorter than the wave form you want to see, look at the .tran values

Well, your simulation certainly does work, I'll say that.

But I'm still in the dark concerning the time interval ("step") setting for the .tran command. What exactly does this do? Yes, I've looked at the online help; it explains nothing.

Does this set the absolute step used in the simulation, the smallest step or what?

[/quote]Also you dont want to see the start up initial conditions.[/quote]

I end up using "uic" a lot too, but the online help advises against it:

Uic is not a particularly recommended feature of SPICE. Skipping the DC operating point analysis leads to a nonphysical initial condition. For example, consider a voltage source connected in parallel to a capacitance. The node voltage is taken as zero if not specified. Then, in the first time step, an infinite current is required to charge the capacitor. The simulator cannot find a short enough time step to make the current nonsingular, and a "time step too small convergence fail" message is issued.

So I guess one ought to use it with care.

Anyhow, thanks again for increasing my knowledge of LTspice.

 

[bloki]

Ziddik is absolutely right. Power supply ripple of only 100uVpp will produce about 200kHz of frequency deviation for the first circuit. Here is taken into calculation only oscillator part of the circuit. This 200kHz of deviation is actually maximum deviation for any FM transmitter and voice from microfone will be practicaly muted.
And a question for some quys here. How many kilos if smoothing capacitors do you need to acheive at least 40dB of S/N for this FM troublemaker?
My admiration goes to India and it's people.

 

[ericgibbs]

cz,
Look at this extract from the web page link.
**broken link removed**

Its explains the use of the 'maximum time step' and what it means.

 

[Ziddik]

i am getting sick of audiogurus "pre emphasis" and "trouble boost", just add a 22n (223) capacitor to couple the sound input..

 

[audioguru]

i am getting sick of audiogurus "pre emphasis" and "trouble boost", just add a 22n (223) capacitor to couple the sound input..

Sorry, but if I make you sick then maybe you should talk about your poor quality FM transmitter on a website in your country in your language.

Pre-emphasis makes an FM transmission sound perfect. ALL FM radio stations have pre-emphasis. Yours has no pre-emphasis so it will sound very muffled without high audio frequencies (something like an AM radio).
Pre-emphasis boosts treble audio frequencies, it does not cut bass frequencies like your idea of a low value coupling capacitor.

 

[bloki]

This FM transmitter is practicaly capable of only telephone voice quality. Thus it needs no pre emphasis so as all variants of this transmitter does not have it.
audioguru is exaggerating all the time and is well known by his arrogance.

 

[Ziddik]

i have said u hundreds of time that its just a simple circuit for noobs (not a profesional one to make a radio station!) so it does't need your "pre-emphasis" nd "trouble boost" ok? We dont want it! Ok? Nd i dont want go to another website, ok? I get better and clear sound output without using ur "pre emphasis" and "trouble boost" (treble).. This is not to start their government approved radio station.