The hack 0.9 describes how to modify a RTL2832U+R820T dongle as RF generator.
I connected the generator to two RTL2832U+R820T receivers and I assumed the generator to be in the 0.5-1.5GHz range as indicated by the receivers screens.
That is not correct because the RTL_SDR receiver is sensitive to even harmonics of the tuning frequency.
The generator output is in the VCO range 1.770 - 3.54 GHz.
The error became evident when I connected the generator to a R&S FSV spectrum analyzer and got the following measures:
Spectrum analyzer settings: Center Frequency 1.8 GHz ; Span 3.6 GHz, Att 10dB.
Generator SDR# tune: 1GHz,
output spectrum: 2.0GHz (2x)
Generator SDR# tune: 0.9GHz,
output spectrum: 1.8GHz (2x)
Generator SDR# tune: 1.4 GHz,
output spectrum: 2.8GHz (2x)
When the generator is tuned to lower frequency the VCO is tuned to higher harmonics (power of 2).
Generator SDR# tune: 0.5 GHz,
output spectrum: 2.0 GHz ( 4x)
The generated signal is weak while clean.