SDRplay Community Forum

Hi All,

I am currently using the SDRPlay via the Osmocom source on GNU Radio. I am running the software on raspbian (Raspberry Pi 3 Model B+). When i start the script it states:
BB + MIX -40 dB ; LNA Gain 0 dB

What does this exactly mean?

What i am trying to figure out is:

I performed measurements with a transmitter of 30 dBm at a distance of 205 meters. Its antenna gain is 3 dBi and the receiver antenna gain is 3 dBi as well. The free space loss is 62 dB. The signal at the RSP2-Pro should therefore be
Signal = 30 dBm + 3 dBi + 3 dBi - 62 dB = - 26 dB.

The measurement shows the signal peak at- 55 dB and signal average at - 65 dB. What is the explanation for this? Is the -40 dB BB + MIX responsible for the 40 dB difference?

Thanks in advance,

Tim

Its antenna gain is 3 dBi and the receiver antenna gain is 3 dBi as well.

If you reduce the problem to it's simplest form, ie. how much power is being transferred from one antenna to another and leaving aside all other considerations, are you taking into account the real-world antenna pattern/s?

-- edit

Just in case that might have sounded lame, it goes to the point that you've specified antenna gains of 3dBi x 2. Because that's gain over an isotropic radiator your 3dB figure implies directionality, ie. 3dB more in some direction at the expense of less radiation in other directions, eg. like a dipole that has a very particular shaped radiation pattern.

Ground, particularly real ground as opposed to an ideal ground then elevates the radiation pattern and breaks it up into smaller lobes so that two antennas at the same elevation are more likely than not to be below each other's major lobes. That may wipe out 6dB or more.

Then there is phasing in regard to Fresnel ground reflections that might add a few dB or cause the loss of few dB, as well as phasing in regard to reflections from anything else in the vicinity which again can influence the path by a few more dB. Perhaps moving one antenna plus and minus 1/4 wavelength towards or away from the other and noting any change in received signal level might be worthwhile.

Then, re your screen dump, I would not have expected that shape from a simple carrier, is your carrier modulated?

Finally, the X axis is in dB rather than dBm with the label relative gain. The highest point on the wave envelope at roughly -60dB may thus be the value of the waveform relative to the baseline and not an indication of the received power level, it may be a measure of voltage rather than power.

Hope that stimulates something and I'm happy to be wrong, so tell me if I am or if I've misunderstood as your heading says "automatic gain". Regards, Phil.