another FM transmitter project

[audioguru]

Again, here is my ASC file (for LTspiceIV)of the RF parts of my Mod4 FM and a photo of the resulting schematic and output waveform:

 

[audioguru]

The 3.23KB ASC file was attached but it opens as a very small 45bytes GIF file instead of the ASC file that opens with LTspiceIV and I do not know why.
I copied the ASC file to my desktop and it opens with LTspiceIV perfectly.

 

[Willen]

May I ask about this little unusual FM Tx? I don't think it can give 12 watt. And how parallel transistor can work at MHz as an RF amplifier? Plz
www.schematicdiagram.s4s.in/2011/07/12-watt-fm-transmitter-circuit.html?m=1

 

[audioguru]

Your link: **broken link removed** does not work.

 

[Willen]

OK this one
https://wireless-schematic.blogspot.com/2011/07/12-watt-fm-transmitter-circuit.html?m=1
Describe there 2 buffer stage, i think these are not amplifier actually.

And also, your ASC file (u attached above) is not working on LT spice. Showing some "invalid schematic..." or somthing like this.

 

[audioguru]

I don't know why my LTspice files do not work when I attach them here.

The new FM transmitter has problems:
1) R1 feeds noise on the 13.8V supply directly into the audio input. Also the value of R1 is too low.
2) The value of C2 is much too high so it cuts high audio frequencies.
3) There is no pre-emphasis so the de-emphasis of all FM radios will make the sound muffled like an AM radio.
4) It is silly to connect 2 little transistors in parallel (buffer2) instead of using a larger transistor that can dissipate the heat.

 

[Willen]

Edited!

 

[audioguru]

My ASC file does not work when I post it here so it probably also will not work when posted in an e-mail.
Besides, if you have my e-mail address then you will probably bother the heck out of me.

 

[Willen]

Besides, if you have my e-mail address then you will probably bother the heck out of me.

If you were a girl of 16, may be i will probably bother you hahahahaha don't worry!

 

[audioguru]

If you were a girl of 16, may be i will probably bother you hahahahaha don't worry!

A girl who is only 16 years old is (was) not yet a woman. But I notice that they are maturing earlier nowadays because some of them are very attractive.
I am a dirty old man who is just looking.

 

[Willen]

A girl who is only 16 years old is (was) not yet a woman. But I notice that they are maturing earlier nowadays because some of them are very attractive.

Yes, time has been changed lot, but I don't like this kind of attractive qualityless girls, men, women, persons.
Sorry,
You are ideal person for me!

 

[transistor495]

A girl who is only 16 years old is (was) not yet a woman. But I notice that they are maturing earlier nowadays because some of them are very attractive.
I am a dirty old man who is just looking.

'Pretty girls are really attractive and makes huge temptation'...

 

[Willen]

Can I add 100nF capacitor parallel with 470R at the emitter of 1st transistor to get pre-emphasis like on Mod-4?

What you think about the performance of this Tx? I think it's so nice!

 

[audioguru]

Can I add 100nF capacitor parallel with 470R at the emitter of 1st transistor to get pre-emphasis like on Mod-4?

The first transistor in your post #365 is the RF oscillator. It oscillates because of positive feedback from its collector to its emitter by C4. If you add a capacitor parallel to its emitter resistor then it will not oscillate anymore.
Pre-emphasis is used for audio, not RF!

What you think about the performance of this Tx? I think it's so nice!

I don't know because I never tested it. It is missing pre-emphasis so its audio will sound muffled. FM is supposed to sound very crisp and clear.
It uses a high supply voltage and has a powerful output stage so its high output power will be very illegal. When it causes interference with an airplane, an ambulance or fire department communication then you will be TORTURED, SHOT and HANGED!!

DONT DOO DAT.

 

[Willen]

The first transistor in your post #365 is the RF oscillator.......

Oh sorry! I forgot to paste the link and you described #365

actuallly asking for this one :-

http://www.talkingelectronics.com/projects/CrystalLockedBug/CrystalLockedBug-1.html

 

[audioguru]

ANOTHER schematic!!
I think that the negative feedback produced by the collector to base biasing will cancel most pre-emphasis if the 470 ohm emitter resistor is bypassed with a capacitor. Bias the first transistor with a normal voltage divider and the pre-emphasis will be the same as mine.

 

[Willen]

The frequency is locked by crystal, then the purpose of the tuned (LC) cricuit is to set higher gain at its resonance friquency, isn't it? But why the inductor has very higher value with ferrite slug than your Mod-4? (even this and your Tx both has same frequency arroung 90MHz).

May be this inductor is not more critical because the designer didn't specified the details about ferrite slug's and wire diameter.

 

[audioguru]

The 10MHz crystal has a 27pf capacitor in parallel and its oscillator operates at the 3rd harmonic at 30MHz. The frequency tripler also operates at its 3rd harmonic at 90mHz.

Details of the size and material of the ferrite slugs and the size and number of turns for the coils are in the parts list.

Notice that the circuit is missing pre-emphasis so it will not sound good.

 

[Willen]

then will remove its Q1 and Q2 and will add your preamp(including pre-emphasis). Done!

 

[audioguru]

I don't know if FM radio frequencies in your country are even (90.0MHz, 90.2MHz, 90.4MHz etc.) or are odd like they are here (90.1MHz, 90.3MHz, 90.5MHz etc.).
I also do not know if this crystal controlled FM transmitter can "stretch" its frequency from 90.0MHz to 90.1MHz without distortion.

Here, many digital FM radios are designed to receive only the odd frequencies.