Microwave Forum

R_F · Rod & Todd Flanders Messages: 6

Hello all people.
I am happy to have found this forum.
I am used to build RF and stuff and now I am planning to build a jammer.
I have some basic questions I hope many of you will share you knowledge.

Ok, some basic.
Since many phones works on dual band 900 and 1800 both must be jammed RIGHT?

Which frequencies are we talking about ?
Here I found some info about frequencies.
http://www.cellular.co.za/gsm-frequencies.htm

GSM900 880 - 915 MHz paired with 925 - 960 MHz
GSM1800 1710 - 1785 MHz paired with 1805 - 1880 MHz
What I understand the jammer should work at the receiving frequency of the phone RIGHT?
So, the jammer should work at 925-960MHz and 1805-1880MHz?

How about the sweep.

At the link above I read that the “The hopping rate is one hop per TDMA frame (4.6µs), or 217 hops per second.”

My question: what frequency of the sweep do wee need?

I have many VCO called
http://www.tdk.com.hk/english/pdf/RF%20Module/VCO/e81112_QVC12.pdf

My frequency measurements of them (dualband) was:
817-975MHz @3V sweep = 0 to 3V
and
1650-1804MHz @3V sweep = 0 to 3V

If I am right above about the frequencies I guess the VCO work at 925 – 960MHz, but not at the high band MHz since the VCO only goes to 1804MHz…

Ok, I will work on and I hope you give me response to my questions .
All help needed..
Regard
my other projects
http://hem.passagen.se/communication/meny.html

richy_64 · Administrator Messages: 198

Hi...

all you said and asked is right.
Nothing to add.

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Excellent vco!!!

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For sweep just use a 10...20 kHz sawtooth signal; better: covered with noise from a noise generator (dirtier = better

)

Greetings,
Richard

__________________________________________________

"Ich liebe es wenn ein (Schalt-)Plan funktioniert."

R_F · Rod & Todd Flanders Messages: 6

Hello again..
Some info and questions for you.

I built a SAW generator and I works from 1kHz to 20KHz.
I connected it to the VCO and connected an antenna of 9cm.

THe VCO only works at 925-960MHz.

Both my Sony CMD-J70 and NOKIA 3310 went dead!!

No reception.. It work about 5m.

My questions...

Why did the phone die? Shouldn't 1800 band work and give the phone signal?
I was surpriced becasue I thought I needed a VCO for 1800 too?

THe range is low, but I think it is because I only use VCO no amplifier right?

I tested to run the SAW generator at different frequencies, but it didn't affect the range...
Do you have any reflections about that?

PLease give me your thoughts and ideas about this...

Regard
D.

richy_64 · Administrator Messages: 198

Hi... (sorry for my bad english)

I built a SAW generator and I works from 1kHz to 20KHz.
I connected it to the VCO and connected an antenna of 9cm.

THe VCO only works at 925-960MHz.

Both my Sony CMD-J70 and NOKIA 3310 went dead!!

No reception.. It work about 5m.

Easy to build, wasn´t it? Congratulations...

----

To your questions...

Actually this circuit can only jam GSM900 but not GSM1800/1900.

Perhaps I didn´t got you right...
Does your Provider use GSM900, GSM1800, GSM 1900 or mixed bands?
In case your provider uses GSM 1800 and the mobile is dead although, maybe the mobile was disturbed by the 2nd harmonics of your GSM900 jammer... I´m not sure if this really works, but theoreticaly it´s possible. I wasn´t able to test this yet, because i don´t have a GSM1800 mobile phone.

But actually you need a jammer for each band...

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The frequency of the sawtooth generator is not critical... mine runs between 10 to 15 kHz, but i didn´t notice that the jammer works worse when it runs at 5 kHz.
Perhaps additional white noise can enhance the range a little bit, mixed to the sawtooth signal.

But 5m range without amplifier is quite good!

The next step is to find a suitable amplifier, the QCPM-9401 is always a good choice...

like i used it in my jammer
http://www.richardsbastelseite.de.vu/

Greetings

__________________________________________________

"Ich liebe es wenn ein (Schalt-)Plan funktioniert."

R_F · Rod & Todd Flanders Messages: 6

Thank you for your reply...

Yes, the phones I used in my test use both bands 900 and 1800, that is why I was surprised that they went dead when I only jammed 900 MHz.....

Well, I will keep investigate...

Now I will go on to build the PA.
I have circuit called PBL 403 05

It delivers 34dBm output power and I want to use it because I have a several of them in a box..
http://hem.bredband.net/b395058/PBL40305.pdf

That is all for now people...
Don't hesitate to write...I need all help I can get...
If anyone is interested I can support you with the VCO circuit and
PA circuit really cheap!

I have tested the VCO at 4.5V !!! Yes it work without problem and the good side is that the VCO range is increased...

Low range is then 817-1038 MHz and the high range is 1653MHz to 1850MHz...

So this VCO can be used fro both bands...

While I am writing I just want to brag a bit about my homebrewed frequency counter I use for this...working great.. :-)
Here you can read about it:
http://hem.passagen.se/communication/frcpll.html

Regard
D.

R_F · Rod & Todd Flanders Messages: 6

I NEED HELP!

Me again...
Ok, look at page 2 in section Electrical Characteristics for PA..there you find note. Pulse operation!!!!!
pulswidth of 577uS...

Also another strange input pin 2 V neg?
Look at this schematic I have:
http://hem.bredband.net/b395058/schem.gif

To me it looks like the power is pulsed to the PA circuit?
TXON at the left seems to be the controlling signal for this pulsing...

I guess that pin 1 and 2 create a negative voltage at pin 2, right?...

When you have a phone close to a radio you can over hear the signal and it sound like buzzing...577uS = 1733 Hz...is it so?

IS it so for all PA that the power pulses?

What do you suggest I do...
Don't say change PA...*LOL*
I want to use this circuit..

You think it will work with constant power and I make a negativ voltage to pin 2?

Please give me your reflections..

All helps needed...*smiling*
Have a great evening now..

D.

richy_64 · Administrator Messages: 198

Hi,
time slot operation is typical for GSM or DECT phones to save bandwith and to reach a higher peak output power.

The amplifier only transmits 577µs, then it can cool down the rest of the frame, 4039µs. So it is 87.5% off!

[A frame is 4616µs long, so the buzzing sound in the radio is ~217 Hz

]

But for a jammer the amplifier has to be most time on. Be careful that you amplifer does not overheat, heatsink is required, the amplifier is originally not designed for that...
I have tested pulsed operation with my jammer... it helps to limit range if you don´t need it... battery lives longer.
For the beginning, always-on transmitting is ok, perhaps set the current limiter at your power supply to 500mA...

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I think Vneg is used for the gate-voltage of the interal Fets; i can´t imagine how this voltage is generated in the schematics... i would just use an ICL7660 instead of adding a negative power supply.
The ICL7660 is a simple voltage inverter chip.
Example: 4V in -> -4V Out

John · Guest

Hi RF,

Can you post the SAW generator circuit here or email me as I was unable to make the jammer work at all ?

Thanks for your help.

R_F · Rod & Todd Flanders Messages: 6

Thanks richy_64,

Great explanation of the time slot…

Yes I understand that the PA must be on all time to sweep the band and to jamm all frequencies for the phone, great…
And yes, heatsink will probably be needed.

From the datasheet i am sure Vneg is needed and I think if you look at schematic again that the 15uF at pin 1 and 2 will pumpa negative voltage to pin 2 since the power to the PA is pulsing…

First I will test with a constant negative voltage. And if that works I will use the oscillator in the SAW to drive a simple voltage pump (inductor + diode +cap ) to create negative voltage…no big deal…

I am now working with the PA circuit to find out how to make it work.
I am making a test pcb for it, damn small circuit…*smiling*

Takes some times to finnish that and to test.
Not sure how to test it…I was thinking to use 50 ohm dummy load and to measure the temp rise in the resistor to verify power…one way…*lol*

I now think I understand why my simple jammer blocked the 900/1800 phone.
I think the 1800 band is not used every where…

This is not a problem becasue if I get the PA working I will go on making a jammer for 1800 band with same curcuits…

That’s all for now people…

And John, I have sent you a mail and I will share all with you people when I get it working as I want…

Regard
D.

John · Guest

Hi Rod,

You are an Ace and I will check your website from time to time.

Thanks again.