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Help needed - The World's simplest transmitter II

 
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Help needed - The World's simplest transmitter II
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Ridgh
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Post Help needed - The World's simplest transmitter II Reply with quote
Hi,
I'll be very thankful if someone may explain me this schematic.
I see 2 oscillators coupled by a 33pF cap. The second one is supposed to oscilate at higher frequency than the first (the variable). after them a buffer stage, as I understand.
I'd like to know why to use 2 oscillators?
I've built the circuit on a vero board, just for testing, without the pre-amp stage. I've got a good JAMMER all over the FM band - from 40MHz up to 200MHZ !!!.
The wierd thing is that on my oscilloscope I can see an almost sinusoidal wave, meaning the upper part is a nice sinus like, but lower part looks more as a line. On the oscilloscope it looks like a stabile about 30 - 40MHz, but on my counter it's about 130-140MHz. Humming is so hard that is impossible to use any receiver in my house at any frequency.
I'll be very thankful for any explanations please.
Thanx in advance.
Tue Jan 03, 2006 11:30 pm View user's profile Send private message
pcs
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Post Reply with quote
It is just one oscillator, actually.

This design is quite unstable, but yields large amounts of power
at lowest possible component number.

In order to get it to work as best as possible you have to follow:

- Carefull component layout, preserve symetrie
- Power supply needs to be RF blocked
- Antenna should be connected via a few meters of coax and placed far away from the transmitter

Still, this is a very basic design, it is not possible to obtain serious performance this way. It is more likely that you will create too much
interference and get yourself in trouble. The proper way to build
a transmitter is to build a PLL, VCO, buffer stages and final stage
plus filtering.

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Best regards,
Marko - PCS Electronics
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Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Wed Jan 04, 2006 5:28 am View user's profile Send private message Visit poster's website
Ridgh
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Post Reply with quote
Thank you very much PCS for responding.
Actually I've built it for JAMMING purpose testing.
I'll explain:
There are - as you know - many small transmitters, PLLs, Xtals, or even simple LC VCOs, and I've built many configurations of them. Most of them are working OK, from the first "shot". Just a weird hobby, as after they seem to work, all goes to my junk box.
Some days ago I've seen on a site a primitive so called Jammer. I don't have the schematics, so I only assume that I'm right:
As I've understood from the guy who built it, it is a simple VCO with a square wave oscillator as an over-modulator, and a potentiometer that he moves if he wants to interface with a station.
As I'm a hobbyist, I began to think how can it be done automatically, meaning the scanning of the entire domestic band instead of the POT.
I thought that instead of the potentiometer to put an optocoupler and modulate it with a sine wave.
The 74HC04 oscillator seemed to be the best option, but as I DON'T HAVE ANY INTENTION OF JAMMING - it does it anyway...nor as using it as a "bug", I'll put it away for now.
I don't know how to make simple RC (not LC) VCO (low power) at the same frequencies, for the same purpose, just for testing the automatic scanning of a jammer.
If you have any idea or any other members have, i'll be very thankful for it.

Best Regards,

Ridgh
Wed Jan 04, 2006 7:20 am View user's profile Send private message
pcs
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Post Reply with quote
Just feed it with 50Hz from mains (on the transformer side, some
5-10V.

_________________
Best regards,
Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Wed Jan 04, 2006 8:05 pm View user's profile Send private message Visit poster's website
Ridgh
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Post Reply with quote

Quote:
Just feed it with 50Hz from mains (on the transformer side, some
5-10V.

A nice joke...
I have one too, about sparkles and Marconi.... a good jammer too
No PCS, this was Not my intention...
Even I've built "The World's simplest transmitter II" on a homemade PCB,
and be sure I've placed decoupling caps all over it, ground plane etc, still have the same endless harmonies all over the scale.
Maybe you have a schematic of a simple VCO, RC , or maybe you know if there is any way to change the frequency to an LC VCO, without touching the inductor or capacitor, by a simple potentiometer. Maybe a varicap may do the job, but a 2-30pF varicap, something as BB105 or others are very hard to be found.
Do you have any other ideas ?

TIA and best regards,

Ridgh
Wed Jan 04, 2006 8:41 pm View user's profile Send private message
pcs
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Post Reply with quote
It was not a joke, 50Hz is a sine and works fine for a jammer.

_________________
Best regards,
Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Wed Jan 04, 2006 8:43 pm View user's profile Send private message Visit poster's website
Ridgh
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Post Reply with quote
Yes, I know that, and on this oscillator may work just perfect for this purpose. But... what I ment was that as I don't need to disturb anyone, I just want to build an R C VCO on those frequencies, that I may control the fequency by a resistor instead a variable cap or variable ferrite inductor.
The guy I've mentioned on my first post changes somehow the frequency by a potentiometer, and I don't know if he uses an LC or RC oscillator.
In conclusion, I need to change the frequency of a 100MHz oscillator to +- 20% by a potentiometer or by changing the voltage somewhere.
Any ideas and help will be very much welcome.
Best regards,
Ridgh
Wed Jan 04, 2006 9:13 pm View user's profile Send private message
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