[Hackrf-dev] Sensitivity

[JMG]

Sensitivity measurements

Test results for the noise figure NF of the HackRF, obtained at a 
frequency of 435MHz:

NF = 22dB               LNA=OFF
NF = 10.8dB           LNA=ON
NF =   1.1dB           LNA=ON, additional external LNA  "LNA4ALL"

RTL-SDR, tuner 820T or 820T2
NF = 3.7dB

The HackRF really is extremely "deaf" when the internal preamplifier is 
turned off. Turning it on and installing
a good external amplifier brings NF down to a very good value.
Applying so much gain at the preamplifiers in front of the mixer will 
degrade the intermodulation properties.
Adding an external LNA will block the transmitter path to the antenna.

The noise figure is the fundamental parameter to specify the sensitivity 
of a receiver. All the other, more common,
sensitivity specifications can be derived from it. For example NF=3dB 
will give an input sensitivity of
S=-174dBm+NF+48dB=-123dBm for typical NBFM signal. The factor "48dB" 
somewhat depends on the test parameters.