Re: SDR operated with a noise source
I don't see here that you understand noise at all well, especially the characterization and measurement of noise. First off, S9+30 dB is in practical terms no more descriptive than, "You have a bodacious signal, OM." My experience with giving calibrated signal level reports and how poorly they were received suggests a properly calibrated S9 point is about as likely as a purple unicorn poaching your breakfast cereal.toggle quoted messageShow quoted text
However, -43 dBm is a fairly large number. If it really is 10 GHz wide then it's level in a 1 Hz bandwidth is about -143 dB. Yeah, that's a fair number to survive insertion of some attenuators for an accurate measurement process. (Boltzmann noise, which you cannot go below, is about -174 dBm, -204 dBm. Note: That's dBm not S "-7" or something. S-Units are "good buddy" measurements for somebody interested in any degree of precision.) Including or not including the bottom 100 MHz is not easily measured compared to leaving out the bottom 100kHz or bottom 1 Hz. The formula for Boltzmann noise is kTB, k = Boltzmann's constant, T is temperature degrees Kelvin, and B is the bandwidth in question.
Hopefully you see the "oops" above. I left out your S9+30 measurement. I don't know the bandwidth you used for measurement. Let's figure you used 10k kHz for AM measurements. Move that up to a 10 GHz bandwidth and you are talking about 60 dB more noise power over that whole 10 GHz bandwidth - it becomes a bit under 1 watt, actually +23 dBm. That is a ridiculously high power level for a noise generator. To measure a noise figure you want a noise source roughly equal in power to the noise figure you wish to measure. Since it would be generating noise at -83 dBm/Hz it's not good for noise figure measurement.
That thumbnail analysis is why I figure you are groping in the dark. There are a lot of good articles to read on the web. Some will probably be at a good starting level for gaining a quick study level of knowledge. And even the highly technical ones are not all that hard to understand when you extract the fundamental numbers and formulas.
On 20210115 03:53:01, Allan Isaacs wrote: