RetroBSD

2.11BSD operating system for microcontrollers
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 Post subject: Re: RC4 encr/decr
PostPosted: Thu Oct 15, 2015 4:25 pm 
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Joined: Mon Nov 12, 2012 1:34 pm
Posts: 1091
Hi Matt,

SDR....

So I have a 20m antenna going through a bandpass filter into an I & Q demodulator then on to a stereo audio card, into one Linrad image, onto a dedicated local ethernet as 16 bit samples, then into another computer running SM5BSZ's Linrad to give a real-time display, then out as audio and into FLDIGI to decode the digital signal.

Works great.

Now can I do that with WIFI? These sorts of things 'must' be being done inside the chip/card. The chip must know LOTS about the received signal and be able to adjust the sent signal in many many ways.

Someday, someone will spill the real beans :).

Lots of fun :).

Wiz


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 Post subject: Re: RC4 encr/decr
PostPosted: Thu Oct 15, 2015 4:36 pm 
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Joined: Thu Oct 11, 2012 8:45 am
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No, you can't "do that with WiFi" because WiFi is a protocol, not a radio.

But a typical WiFi chip will be doing similar things, with lots of frequency synthesis, etc.

The modulation techniques used for WiFi are somewhat more complex than your typical AM or FM transmissions. You have QAM (combination of Quad-PSK and AM), spread spectrum, etc - all far more complex than you can hope to achieve with simple bandpass / demodulate / sample etc.

SDR systems are generally more suited to digital communications than analog - so things like QAM can be demodulated easier using SDR than discrete components - since the input and output of the system are both digital.

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 Post subject: Re: RC4 encr/decr
PostPosted: Thu Oct 15, 2015 5:31 pm 
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With pic32MZ (or STM32F4/7) you can do it. You need a frontend (a downconverter - mixer from 2.5GHz band down to a few MHz (or a fraction of MHZ - here depends on the data rate you want to process), I/Q) and then you sample simultaneously the I/Q output via 2 ADCs (the built in ones, "simultaneous conversion" is important here). Then it is a matter of DSP math algorithms, floating point is a big advantage here. There are megatons of frontend chips available. That is how ALL the today's digi radio systems/chips work. ;)

For example the low cost digi TV usb dongles work that way - a primitive bandpass filter (or none), a mixer down to ~fewMHz I/Q, 2 simultaneous 6-8bit ADCs and then a lowpass digifilter - the data are then shifted out via a highspeed usb into the PC, PC is then doing the demodulation math (you may demodulate any kind of digi modulation schemes, inclusive analog ones - AM, FM, NFM, USB/LSB, etc.). A tons of open source sw does exist for these dongles. The dongles work from 5-2500MHz and cost $10.
PS: off the retrobsd scope, of course.. Pls start a new topic for that, or ask us to start it for you..

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 Post subject: Re: RC4 encr/decr
PostPosted: Thu Oct 15, 2015 7:09 pm 
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Joined: Mon Nov 12, 2012 1:34 pm
Posts: 1091
Hi Pito and Matt,

The MZ..EF does/claims to do 28mhz 12 bit samples, [maybe?]. And has DSP instructions built in!

I want to see it! The MZ should be able to sample the stereo audio just mentioned and format it into packets for transmission over my local internet. I can't wait to try it out!!

Linrad provides a way to restrict the number of bits it uses. Generally you don't need 16 bits and can't see any problems until there are many fewer bits coming in. Not what I would have expected.

Anyways the MZ by itself should make a pretty good radio :). Except for no real DAC on board.

Some of the early WIFI boards had pretty limited ADCs also but seemed to work OK.

So Pito you could probably hook a radio antenna with maybe some diode protection to an ADC pin on the MZ and have it receiving radio signals.

FWIW-The USB dongles I have need USB2 which is a LOT of data.

Lots of fun :).

Wiz


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 Post subject: Re: RC4 encr/decr
PostPosted: Thu Oct 15, 2015 7:09 pm 
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Joined: Mon Nov 12, 2012 1:34 pm
Posts: 1091
Hi Pito and Matt,

The MZ..EF does/claims to do 28mhz 12 bit samples, [maybe?]. And has DSP instructions built in!

I want to see it! The MZ should be able to sample the stereo audio just mentioned and format it into packets for transmission over my local internet. I can't wait to try it out!!

Linrad provides a way to restrict the number of bits it uses. Generally you don't need 16 bits and can't see any problems until there are many fewer bits coming in. Not what I would have expected.

Anyways the MZ by itself should make a pretty good radio :). Except for no real DAC on board.

Some of the early WIFI boards had pretty limited ADCs also but seemed to work OK.

So Pito you could probably hook a radio antenna with maybe some diode protection to an ADC pin on the MZ and have it receiving radio signals.

FWIW-The USB dongles I have need USB2 which is a LOT of data.

Lots of fun :).

Wiz


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 Post subject: Re: RC4 encr/decr
PostPosted: Thu Oct 15, 2015 9:11 pm 
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Joined: Thu Nov 08, 2012 7:04 am
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Location: Rapa Nui
Quote:
So Pito you could probably hook a radio antenna with maybe some diode protection to an ADC pin on the MZ and have it receiving radio signals.

That is how this gadget works for example:
http://websdr.ewi.utwente.nl:8901/
They sample an antenna directly with a 66MHz ADC thus streaming out via web 0-30MHz signals you may decode and listen inside your browser (an online web based SDR radio). Old stuff already :)
73, P.

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