Discuss RTL-SDR and cheap software defined radio
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 Post subject: Signal Level Question
PostPosted: Sat Aug 19, 2017 6:43 pm 

Joined: Sun Aug 13, 2017 7:28 am
Posts: 1
I am attempting to make sense of several different readings from my RTL-SDR.

I have the RTL-SDR connected to a 50 ohm load. Removing the load, leaving the RF input disconnected increases the base level by some 0.2 dB. Seems strange.

I can not correlate the levels seen by SDR# and rtl_sdr or python applications.

I calculate power from i-q as
db_level = 10*log10( (i^2 + q^2) / 100 ).
dbm_level = 10*log10( 10 * (i^2 + q^2) ).

I think the mean value of this calculation should be close to the value seen by SDR#. It is not.

Data collected by rtl_sdr from librtlsdr tools
##/tmp/rtl_sdr.bin -63.218705 dB
##/tmp/rtl_sdr.bin -33.218705 dBm
##/tmp/rtl_sdr.bin -45.726986 psd dB

Data collected with pyrtlsdr functions
##/tmp/sdr_collect.bin -64.747267 dB
##/tmp/sdr_collect.bin -34.747267 dBm
##/tmp/sdr_collect.bin -48.284199 psd dB

Data observed in SDR#
## sdr# gain 49.6 dB AGC off 1.420 GHz
## 1.420 GHz peak -54.8 dB
## floor -55.4 dB
## SNR 1.5 dB
## Signal Diagnostics
## full iq
## ref 0.0 dB
## Amplitude -43.1 dB

Since the rtl_sdr and pyrtlsdr data sets were collected at different times, the values are considered equal.

Both these values differ from that observed with SDR#.

What am I doing wrong???

Tom Dean

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