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Any suggest for voice scrambler

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Andy M

Newbie level 3
Oct 1, 2002
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inverted spectrum scrambler

Dear All

Does any one have idea to make a low cost voice scrambler for walkie-talkie? I need this for my final year project. Can any one help? Thank you!

Best Regards

Andy M

voice scrambling matlab

Hi Andy!

Simplest way to scramble signal is to invert spectrum of this signal.
You will need generator, multiplexer and some filters for one way scrambler. Discrambler will be the same. Will it be enough for your final-year project?

If you need more simple circuit you can look to FX224J, or FX224LG ic.

Best Wishes! 73! Klug.

voice scrambler


Klug is right,

The simplest way is to build a spectrum inverter.
You'll need a generator, above the audio spectrum, for example at FG=3.3kHz. This generator must be multiplied with your microphone AF ( FA=(0.3 to 3kHz), it can be done with the aid of a frequency mixer. As a result you will have two products : (FG+FA) and (FG-FA). The sum product is above 3kHz and is unusable, because you can't pass this product via a walkie-talkie, and must be filtered by a 3kHz low-pass filter. After the LPF you will find your AF inverted - low frequencies are on the high end and vice versa. On receive, above mixing and filtering must be done again to recover original AF.
This way of scrambling is not effective, it is very easy to intercept such a signal, but is very simple and cheap.
If you need something more complicated, take a look at CML site and search for IC's, referenced by Klug.
Give me (PM me) your e-mail address. I'll post you an example schematic.


PS: Klug, 73 from LZ land.

voice scrambler microphones can,t

well thats true, but maybe the cheapest and easiest way is to do a conv within matlab (in the case matlab is available). stream the input into a vector, and you can do any algorithm ...

scrambler for walkie circuit

Thanks to all

The information is very useful. I have propose both complex and single chip solution to Dr. and is waiting for his reply. In fact, I'd like to use the single chip solution. It is very effective and more consistent.

Can the mixer frequency as low as 1.5KHz, since normally, our voice is below 1KHz.

voice scrambler matlab

Hi Andy!

Our voice is below 3 kHz and you need frequency of generator more then 3 kHz - if band will be 0.3 - 3 kHz than your carrier need to be on 3.3 kHz. Also you will need good multiplexer that will not pass your incoming signal to out.

I have found a scheme of such scrembler, it is in russian but I can translate much difficult words :) ... There are some mistakes on this scheme, so you will have enough field for creative work . :)

DA1 - any double amplifier.
DA2 - CD4066
DD1 - CD4013
DA3 - 555 timer

**broken link removed**

Best Wishes! Klug.

P.S. 73 comes to STOYANOV! Regards from ER.

voice scrambler circuit


You can filter at 1 kHz and mix at 1.5 kHz if you can live with the sound quality. However, I am not familiar with the chips so you must decide for yourself.


how does voice scrambler work

Thanks a lot

voice scrambler+matlab code

can any one conform it about this ckt , will it works if some one conform it i will make pcb for the same with all correction and gift to all just here.

i think it is ok but the filter section value might be wrong.

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