@immy, i would change your circuit like this.
What is the oscillators frequency? Change C1 to get 10-20kHz.
I think some nF will be suitable for this.
Use an oscilloscope to measure at the output. Now you can adjust the waveform you want...
For example: To get a signal from 17-23V, set the "DC Offset"-resistor to get 20V, then turn the "Noise Amplitude"-resistor to get 17-23V.
It will work!
@imgemini
Are you able to take a picture of your noise generator´s output signal with an oscilloscope?
This would help much.
ok i will take the picture of my noise 0gen signal and wil try this circuit also
but i want to know why its not shopwing anything on ths ouput pin when i give
13.5v dv noise signal
Vcc =10
output= anthing
i hope i conned right wire bcoz it not 
Coaxial Cable
To get higher frequencies, try this:
R1=3,3k
R2=1k
C1=100nF
The LEDs can be left away.
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I ALSO RECOMMEND THE FOLLOWING:
@imgemini: please take a picture of this output signal, too. Thanks.
hi
here is the cricuit
here is the signal ....
anthing in khz just in hz i think 0.5hz only
i tune with POS1060 with that bout get anthing on output 
here is the ouput singal odf POS1060
plesae both of you can tell me wwhat is wrong .....and what should i do now
Re: what is that MAR-8 driver
hello...
....maybee our ne555 circuit deliver to less output....!!!
(damn ne555!!!)
try messure with and without connect to the VCO...
so you can see how much ne555 able to drive ...!!!
send some picures with voltage per division
and time per division.
so i can read our circuit right.
Chris
p.s. better use my sawtooth circuit (8->) !!!
hi
plesae clear these trams for me
why i need 10 to 20kh?
if this is my result as show above then what should i do know to get 10 to 20 khz
plesae friends reply
These pictures are not useable for anyone without descriptions like volt per division and time per division...
The 2nd picture: You have measured the POS1060 output??
What is your oscilloscope´s bandwith? 
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The sweep frequency to modulate the vco has to be "high".
If the sweep frequency is too low the jammer won´t work, because the gsm error correction can handle short interferences.
To get a higher frequency, change R1,R2,C1.
I have mentioned it above already.
@ Chris
Everyone uses/knows the NE555.
I don´t like it, too.
I don´t know why 
