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### Topic: Would this circuit work? (Read 1 time)previous topic - next topic

#### manray

##### Feb 22, 2013, 04:18 pm
I am doing my senior project now and finally finished designing the circuit, but my professor told me that it wouldn't work but didn't say why, and I have spent a couple hours looking it over with no luck. Can someone tell me if this would work? And if not, why?

#### Papa G

#1
##### Feb 22, 2013, 04:23 pm
This definitely won't work as you've left out the Arduino.

#### retrolefty

#2
##### Feb 22, 2013, 04:23 pm
Quote
And if not, why?

Simple, that output of the amplifier after the series 50 ohm resistor is shown being wired to ground, thus no current can flow out the antenna connection.

Lefty

#### majenko

#3
##### Feb 22, 2013, 04:26 pm

Quote
And if not, why?

Simple, that output of the amplifier after the series 50 ohm resistor is shown being wired to ground, thus no current can flow out the antenna connection.

Lefty

That is exactly what I was going to query...

Also...

What is the circuit *supposed* to do?

#### Papa G

#4
##### Feb 22, 2013, 04:34 pm

Quote
And if not, why?

Simple, that output of the amplifier after the series 50 ohm resistor is shown being wired to ground, thus no current can flow out the antenna connection.

Lefty

That's to impedance match the grounded antenna on the input.

#### manray

#5
##### Feb 22, 2013, 05:48 pmLast Edit: Feb 22, 2013, 06:02 pm by rickburgen Reason: 1
I am aware of the ground at the antenna problem. My question is with the overall concept of the schematic.Is to broadcast frequencies across the entire bandwidth of the monolithic amplifier we bought. Another idea i had was to have a square/triangle wave feed into the mixer instead of the input antenna. I am not familiar enough with the output of the mixer but the idea is to block all frequencies. The professor seems to feel the input antenna would mostly pick up the signal from our own output antenna and not surrounding signals.

#### JimboZA

#6
##### Feb 22, 2013, 05:53 pmLast Edit: Feb 22, 2013, 06:07 pm by JimboZA Reason: 1
Quote
My group is making a frequency jammer with a wide enough band width to block cell phones and wifi

Which might just be enough information to get people to stop helping you if that would be aiding and abetting some kind of illegal act....

Edit... this post was in response to a post of the OP which has since been edited not to include the above quote. (Just in case any other members are wondering wtf I'm making up, here  )
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### JimboZA

#7
##### Feb 22, 2013, 06:02 pmLast Edit: Feb 22, 2013, 06:05 pm by JimboZA Reason: 1
If I were you I'd look into the law where you are and see what your national communications authority would think about jamming the airwaves, school approved or not.

Edit... this post was in response to a post by the OP which has since disappeared
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### retrolefty

#8
##### Feb 22, 2013, 06:25 pm

I am aware of the ground at the antenna problem. My question is with the overall concept of the schematic.Is to broadcast frequencies across the entire bandwidth of the monolithic amplifier we bought. Another idea i had was to have a square/triangle wave feed into the mixer instead of the input antenna. I am not familiar enough with the output of the mixer but the idea is to block all frequencies. The professor seems to feel the input antenna would mostly pick up the signal from our own output antenna and not surrounding signals.

Your Prof is correct in that the circuit is much too incomplete to be used as a 'cell phone' jammer. the heart of you circuit is a simple frequency mixer IC, which takes two input signals and creates both the sum and difference of those two frequency inputs and outputs it where you then use an output filter to eliminate either the sum or difference component and send the other component onto the amp stage. So you trying to mix a fixed 50Mhz carrier frequency with an input that is not filtered and as such 'looking' at the total RF spectrum band, so in effect you have nothing but noise to mix with.

A simpler 'cell phone jammer' would utilize a VCO (voltage controlled oscillator) designed to cover the output frequency band of interest and you feed the VCO a triangle wave such that the RF output would be a continuously ramping output carrier frequency covering the full output frequency range of the VCO which could then be amplified to any level you wished.  And of course such a device is illegal to operate, as intentional jamming of a public service carrier is not allowed in any country that has such service available.

Here is a typical VCO module covering a specific RF frequency range:

http://www.minicircuits.com/pdfs/POS-1060.pdf
Lefty

#### manray

#9
##### Feb 22, 2013, 06:46 pm
Thanks Lefty. Ill take a look at that. I have no intentions for using this project for any type of malicious attack or illegal conduct. its simply something I've been interested in and what better motivation to work on something I'm interested in than seniors project.

#### KeithRB

#10
##### Feb 22, 2013, 06:57 pm
We fully believe that you love puppies and have no evil intentions, but just *turning it on* is illegal!

#### billhowl

#11
##### Feb 23, 2013, 12:27 am

And if not, why?

The Mixer is operate on 3.3V and you feed 5V
The RF input need about -6dBm signals and input from Antenna will get some thing like -70dBm or less, you need amplifier

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