RFgenmod

The RTL2832+R820T RF GENERATOR hack

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by Oscar Steila ik1xpv, ver 0. 9

2015.06.18


RTL-SDR is a very cheap software defined radio that uses a DVB-T TV tuner dongle based on the RTL2832U chipset.

The most common today RTL-SDR dongle contains two primary chips: the Raphael Micro R820T radio tuner and than the Realtek RTL2832U which contains an 8-bit ADC and USB data pump.

During last year the R820T chip has been substituted by the R820T2 with a little better receiver performance.

I bought some R820T2 dongles and I needed a RF generator in the GHz range for comparison.

I investigated the possibility to modify a RTL2832U+R820T dongle to use it as a Radio Frequency Generator and hereafter the results.

The R820T block diagram shows that the internal VCO has no output pin.


The idea is to use the pin 5 (Det2) that is related to the mixer output. Of course it is not thought to be a RF output, nevertheless part of VCO signal is routed out.


WARNING the modified dongle is no more a RTL-SDR receiver.

It becames a RF generator in the 500-1500 MHz range.  ( see Update 1.0 )


The hardware modification is:

Options:

Refer to the following pictures of the hardware modification.




The following screenshots has been saved while using a RT2832U+R820T2 dongle as receiver and the modified RT2832U+R820T dongle as generator. Generator and Receiver are connected via a coax cable .

( NOTE: the RTL_SDR receiver is sensitive to harmonics of the tuning frequency.  

The generator output is in the VCO range  1.8 - 3 GHz. See Update1.0  )

A SDR# application is used to operate the Receiver, while a second SDR# application is used to program the Generator dongle frequency.  It is necessary to program the required VCO frequency Shift to compensate the IF offset of R820T.

The development of a specific application for the Generator is scheduled in Summer.






Notice the DVB-T signal reception on the left.




The RF generator has an usable range of 500-1500MHz and the output level is a little weak.

That is not correct! why the RTL_SDR receiver is sensitive to even harmonics of the tuning frequency.

The generator output is in the VCO range  1.8 - 3 GHz. See Update 1.0


Future ideas:

The possibility to FM modulate the signal must be verified. The pll filter looks accessible. A PC audio output could be injected to the filter via an attenuator.


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