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.
The hardware modification is:
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
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.