Can any RF chip be modded to turn into an sdr or only R820T?

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bugdetector
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Can any RF chip be modded to turn into an sdr or only R820T?

Post by bugdetector » Sat Aug 22, 2020 10:34 pm

Can any RF chip be modded to turn into an sdr or only R820T? Can a person program their WiFi adapter to turn into an SDR covering frequencies upto 2.4GHz or 5GHz?

If yes, why aren't there sdrs with USB WiFi modules?

alanzfq
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Re: Can any RF chip be modded to turn into an sdr or only R820T?

Post by alanzfq » Sun Aug 23, 2020 10:28 am

The R820 is not a SDR chip it is in fact nothing to do with SDR simply a tuner.
The SDR chips are analogue to digital converters, the RTL chip in RTL dongles is an ADC, could have any tuner chip in front of it, or none at all. If you really feel like modding it go ahead.
Alan

bugdetector
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Re: Can any RF chip be modded to turn into an sdr or only R820T?

Post by bugdetector » Sun Aug 23, 2020 8:07 pm

alanzfq wrote:
Sun Aug 23, 2020 10:28 am
The R820 is not a SDR chip it is in fact nothing to do with SDR simply a tuner.
The SDR chips are analogue to digital converters, the RTL chip in RTL dongles is an ADC, could have any tuner chip in front of it, or none at all. If you really feel like modding it go ahead.
Alan
Thanks for this information.

If there is no tuner, how will ADC capture any frequency?

Shouldn't USB WiFi modules have an ADC in them as they also deal with radio signals? Do you think they have a tuner as well? Can a USB WiFi modules with RTL8811AU be software modded to turn it into an SDR? Or does it require to be hardware modded as well, with a tuner in front, etc?

alanzfq
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Re: Can any RF chip be modded to turn into an sdr or only R820T?

Post by alanzfq » Mon Aug 24, 2020 6:55 am

An ADC will accept radio signals but limited by it's sample rate. You use a tuner (converter) to extend it's range.
I know nothing about WiFi modules and have seen nothing about modifying them.
Alan

hotpaw2
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Re: Can any RF chip be modded to turn into an sdr or only R820T?

Post by hotpaw2 » Mon Aug 24, 2020 3:01 pm

Depends on what you mean by an SDR. Most WiFi, cellular, and mobile phone radios are SDRs internally. So you don't need to turn them into an SDR, as they already are SDRs.

However the RF frequencies and modulations these SDR chips are capable of are often fixed to specifics bands and modes, and the ADC/DAC streams connect only to fixed function DSP blocks. So you can't use these SDR chips as general purpose SDRs (e.g. tune to interesting signals and then get the ADC data out of the chip to your SDR software).

Note in this block diagram that the ADC/DAC is only connected to the baseband PHY and MAC blocks, not the IO or processor, and there is no separate tunable oscillator block. https://www.cnx-software.com/2016/08/01 ... wifi-socs/

The RTL2832 was interesting due to the fact that a downsampled IQ stream was exposed to the USB port driver, and the tuner chips used with the RTL chip were flexible enough to be programmed to go to interesting frequencies (e.g. more than just DTV). Without those two capabilities, it would still be an SDR, but an SDR only useful for watching broadcast DTV.

bugdetector
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Re: Can any RF chip be modded to turn into an sdr or only R820T?

Post by bugdetector » Mon Aug 24, 2020 7:44 pm

hotpaw2 wrote:
Mon Aug 24, 2020 3:01 pm
Depends on what you mean by an SDR. Most WiFi, cellular, and mobile phone radios are SDRs internally. So you don't need to turn them into an SDR, as they already are SDRs.

However the RF frequencies and modulations these SDR chips are capable of are often fixed to specifics bands and modes, and the ADC/DAC streams connect only to fixed function DSP blocks. So you can't use these SDR chips as general purpose SDRs (e.g. tune to interesting signals and then get the ADC data out of the chip to your SDR software).
Are they fixed to specific bands and modes through hardware or software. Will it be difficult or impossible to make the DSP pass that data through USB? Can the DSP be used to process the signal, reducing the computational load on the main processor.
hotpaw2 wrote:
Mon Aug 24, 2020 3:01 pm
Note in this block diagram that the ADC/DAC is only connected to the baseband PHY and MAC blocks, not the IO or processor, and there is no separate tunable oscillator block. https://www.cnx-software.com/2016/08/01 ... wifi-socs/

The RTL2832 was interesting due to the fact that a downsampled IQ stream was exposed to the USB port driver, and the tuner chips used with the RTL chip were flexible enough to be programmed to go to interesting frequencies (e.g. more than just DTV). Without those two capabilities, it would still be an SDR, but an SDR only useful for watching broadcast DTV.
Thanks for that link. I opened up a USB WiFi adapter I have and it had an oscillator on the other side. I couldn't make out the numbers and alphabets printed on the ICs before the RTL chip, but I don't think they are tuner ICs. Would you happen to know about any hardware hacking and reverse engineering forums?

LB6MI
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Re: Can any RF chip be modded to turn into an sdr or only R820T?

Post by LB6MI » Tue Sep 08, 2020 8:40 pm

Any chip you can get the access to the digital "RF/IF" data from is a useable SDR.

There are plenty possible chips you can use, RTL-SDR just offers a USB interface making use with computers easy.

LimeSDR have a transciver, analog devices & texas intruments have plenty.

Or you can build your own using mixers, filters, frequency synthesizer(PLL+Oscillator), ADC(analog to digital converters), some kind of processor to do the digital processing.

R820T is just a front-end in order to make the reciever cover 24 - 1700 MHz, instead of 0-14 MHz.
It basically converts a smaller slice of the wide range into the smaller range at a lower frequency.

You can totally do the R820T with discrete parts, but it would be quite many parts!

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