another FM transmitter project

[Willen]

My oscillator is powered from regulated 5V. The base of the oscillator is about +3.33V, not +5V.
A 5.1V zener diode can be used (with a series resistor from +9V) to power the oscillator and preamp. But a zener diode wastes battery power.

All Western semiconductor manufacturers make low-dropout 5V regulators.

- A series resistor from 9V like this ? www.circuitdiagram.org/stable-fm-transmitter.html
But how to seperate 5V for oscillator and 9V for Amplifier?
- I found a unusual circuit. There are no regulated supply on oscillator. But there is a varactor and crystal in previous stage. How it can be stable?
www.circuitdiagram.org/crystal-controlled-fm-transmitter.html

 

[audioguru]

- A series resistor from 9V like this ? www.circuitdiagram.org/stable-fm-transmitter.html

No.
That circuit is completely wrong. The circuit is powered from +9V and the zener diode does nothing.
The entire circuit should be powered from the zener diode and only the 1k resistor that powers the zener diode should be connected to the +9V battery.

I found a unusual circuit. There are no regulated supply on oscillator. But there is a varactor and crystal in previous stage. How it can be stable?
www.circuitdiagram.org/crystal-controlled-fm-transmitter.html

Its frequency is stable because it is fixed to one frequency (149.58MHz which is the third harmonic of the crystal oscillator) by the crystal. The varactor diode modulates the frequency slightly producing FM.
I don't think the oscillator will produce the second harmonic at 99.72MHz.

 

[Willen]

No.
That circuit is completely wrong. The circuit is powered from +9V and the zener diode does nothing.
The entire circuit should be powered from the zener diode and only the 1k resistor that powers the zener diode should be connected to the +9V battery.


Its frequency is stable because it is fixed to one frequency (149.58MHz which is the third harmonic of the crystal oscillator) by the crystal. The varactor diode modulates the frequency slightly producing FM.
I don't think the oscillator will produce the second harmonic at 99.72MHz.

-But I heared that 5V zener diode (in reverse) will pass above 5V (it will ground above 5-9V in 9V supply), then how i can connect it at series of 9V supply? Shouldn't i have to connect zener to ground?
-This is similar crystal controlled circuit. www.radio-circuits.com/bbg.htm There is a sentence :

If I use a 15 Mhz Barrel Crystal, the frequency at Q4s output is: Xtal X 5 Or: 75 Mhz into Q5. Q5 Multiplies 75 Mhz X 2 for an end frequency out of the final Q6 (Desired Output Frequency ) of 150.00 Mhz.

if it is, can i use 10MHz crystal for 100MHz? How can I tune desired friquency? There, any VHF transistor will work fine?

 

[audioguru]

-But I heard that 5V zener diode (in reverse) will pass above 5V (it will ground above 5-9V in 9V supply), then how i can connect it at series of 9V supply? Shouldn't i have to connect zener to ground?

There is a 5.1V zener diode available but not a 5.0V zener diode.
It is fed a positive voltage through a series current-limiting resistor and holds the voltage across it to 5.1VDC. Its anode connects to 0V and the positive side of the circuit that it powers and the 1k resistor that feeds it connect to its cathode.
With a 9V supply the zener diode conducts (9V - 5.1V)/1k= 3.9mA to ground. If its load draws more than 3.9mA then the voltage drops to less than 5.1V. If the input voltage to the 1k resistor that feeds it drops then the zener diode current drops. When its current is close to zero then it fails to regulate the voltage.
My oscillator draws about 10mA so the 1k resistor feeding the zener diode has a value that is much too high. if the resistor value is reduced so the zener diode regulates properly then the zener diode will waste a lot of battery power.

Can i use 10MHz crystal for 100MHz? How can I tune the desired frequency?

You cannot tune a crystal oscillator. Here in North America digital FM radios tune in only 99.7MHz, 99.9MHz, 100.1MHz, 100.3MHz and other odd frequencies. These radios do not tune in 100.0MHz which is an even frequency. I don't know what frequencies are used in your country because some countries use even frequencies.

The Rohm BH1415 to BH1417 FM stereo transmitter ICs used a crystal-controlled frequency synthesizer circuit where you could select one of 8 frequencies with a switch. The frequency was crystal-controlled so it was very stable.

You might learn about radio circuits and crystal oscillators some day.
A crystal oscillator without a resonant LC circuit produces a square wave output. A square wave has only odd (not even) harmonics like 3 times, 5 times or 7 times the fundamental frequency. The article says its oscillator produces 5X which is 5 times. Another transistor doubles the frequency (2X). Then the output frequency is 5 x 2= 10 times the crystal frequency.

There, any VHF transistor will work fine?

Any general purpose transistor like a 2N2222 or 2N3904 will work fine as a VHF oscillator.

 

[Willen]

OK!
I will use 10MHz Xtal for 10x5=50 and 50x2= 100Mhz (arround odd of 100MHz)
But when I change crystal of this circuit, should I have to modify the collector inductors?

 

[audioguru]

OK!
I will use 10MHz Xtal for 10x5=50 and 50x2= 100Mhz (arround odd of 100MHz)
But when I change crystal of this circuit, should I have to modify the collector inductors?

The resonant LC circuit at the output of the x5 stage must be tuned to the 5th harmonic. To produce odd harmonics the oscillator must have symmetrical clipping.

The resonant LC circuit at the output of the x2 stage must be tuned to the second harmonic of the output of the previous stage. To produce even harmonics the stage must clip only one half of the waveform.

Can digital FM radios in your country tune in 100.0MHz? Not in North America.

 

[Willen]

The resonant LC circuit at the output of the x5 stage must be tuned to the 5th harmonic. To produce odd harmonics the oscillator must have symmetrical clipping.

The resonant LC circuit at the output of the x2 stage must be tuned to the second harmonic of the output of the previous stage. To produce even harmonics the stage must clip only one half of the waveform.

Can digital FM radios in your country tune in 100.0MHz? Not in North America.

I know nothing.
I just want to replace 10MHz crystal to produce any one friquency between 88-108MHz. Can't I?

 

[audioguru]

I just want to replace 10MHz crystal to produce any one friquency between 88-108MHz. Can't I?

No.
A 10MHz crystal x10= 100.0MHz which might not be an FM radio channel in your country or it might already be used.
A 12MHz crystal x10= 120.0MHz which is too high.

Newark in America list 700 quartz crystals. Suitable ones might be 8.912MHz, 9.216MHz, 9.8304MHz and 10MHz.
They have thousands of 9.8304MHz crystals in stock. Then you can transmit on 98.3MHz.

They also have some crystals with frequencies near 20MHz so you can use a x5 stage and transmit near 100MHz.

 

[Willen]

No.
A 10MHz crystal x10= 100.0MHz which might not be an FM radio channel in your country or it might already be used.
A 12MHz crystal x10= 120.0MHz which is too high.

Newark in America list 700 quartz crystals. Suitable ones might be 8.912MHz, 9.216MHz, 9.8304MHz and 10MHz.
They have thousands of 9.8304MHz crystals in stock. Then you can transmit on 98.3MHz.

- Um...If i change crystal (friquency) then I should modify these inductors little, isn't it? (you said before something)
-

They also have some crystals with frequencies near 20MHz so you can use a x5 stage and transmit near 100MHz.

OH! Amazing! Can I also remove ''x2 stage'' and connect RF output direct to antenna? Like 20x5=100MHz by removing x2 stage? Wow!

 

[audioguru]

- Um...If i change crystal (friquency) then I should modify these inductors little, isn't it? (you said before something)

You must tune the LC resonant circuit for a peak at the operating frequency by changing the capacitance of a trimmer capacitor or changing the inductance by turning a ferrite slug or changing the spacing between the turns of the coil.

Can I also remove ''x2 stage'' and connect RF output direct to antenna? Like 20x5=100MHz by removing x2 stage?

Yes if the x5 stage has enough output power.

Do you have a vacant FM radio frequency available? Here there are hundreds of FM radio stations on almost all frequencies so a vacant frequency is hard to find.

 

[Willen]

Do you have a vacant FM radio frequency available? Here there are hundreds of FM radio stations on almost all frequencies so a vacant frequency is hard to find.

Here lots of friquency are vacant. In my country, FM has started ONLY 14/15 yrs ago. And only 2/3 stations here at 2005. Now in my area, 14 strong stations I can listen. Other 2/3 week stations i cannot listen well. So I have great chance to experiment with FM transmitters. Here 91-93MHz and 100-108MHz friquencies are amlost empty. Others are partially empty so I can get vacant almost anywhere!

 

[audioguru]

In my country, FM has started ONLY 14/15 yrs ago.

I built a mono FM radio kit in 1962 which was 50 years ago. One year later I built a kit stereo adapter for it.
They used vacuum tubes.

Old TVs always used FM for sound.

 

[Willen]

I built a mono FM radio kit in 1962 which was 50 years ago.

My mother was born at 50 years ago
WOW! You have a great experience of electronics from Vacuum tubes to micro-chips! Arround 1950s/60s had you imagine this kind of development in electronics field? In 1969, how Neil Armstrong can land on moon using such old and begining electronics and technology!!??!!
All things are so interesting!!

One year later I built a kit stereo adapter for it.
They used vacuum tubes.
Old TVs always used FM for sound.

I never seen Vacuum tubes, so I searched on internet to see this components and found a AM receiver which has used vaccum tube.
There is no FM sound in Modern TVs?

 

[audioguru]

There is no FM sound in Modern TVs?

Old TVs were analog. The vacuum tube screen (CRT) used scanning lines for position of the dot on the screen and amplitude modulation (AM) for brightness or darkness. The sound was FM.
Modern TVs in the West have an LCD or plazma screen and are digital and high definition now. The sound is digital like on a CD.
In a couple of years modern TVs will be ultra high definition.

In the 50s and 60s I did not imagine the internet, the modern digital very thin TV screens today and that everybody will have a cell phone with the internet, with a camera and plays videos.

 

[Willen]

Hope that the schematic is ok. Ok? www.techlib.com/electronics/spherics.htm

(On this site, he has various RF schematics like Super tiny VLF receiver, All band receiver, a circuit to detect static charge etc which makes me really amazing!)
I am trying to them...

 

[Willen]

Placing a ferrite core inside an air core coil will increase the inductance. But what happen if I covered an air core coil using ferrite pipe? I am placing 5mm air core coil inside a 6mm ferrite pipe. Will this increase inductance too? I don't have testing device.

 

[Willen]

Its frequency is stable because it is fixed to one frequency (149.58MHz which is the third harmonic of the crystal oscillator) by the crystal. The varactor diode modulates the frequency slightly producing FM.
I don't think the oscillator will produce the second harmonic at 99.72MHz.

www.circuitdiagram.org/crystal-controlled-fm-transmitter.html
Do you have any idea to make friquency between 88-108MHz by replacing crystal or removing any stage? Doing anything

Can't I use 30MHz cryatal to get 3rd harmonic of 90Mhz?

 

[audioguru]

Do you have any idea to make friquency between 88-108MHz by replacing crystal or removing any stage?

For many years, FM receivers use a crystal in a frequency synthesizer circuit. The Rohm FM stereo FM transmitter ICs used the same idea. Then many very accurate frequencies can be selected. I have never tried it.

Can't I use 30MHz crystal and use 3rd harmonic to make 90Mhz?

Yes.

 

[Willen]

Yes.

Sorry confuse on your short answer . Yes= I Can or I cannot?.

 

[audioguru]

Yes= you can.