Friday, December 14, 2007

SDR Sensitivity Measurements

Anonymous made a comment to my previous post: "These are the first measured of sensitivity or comparasions with other SDR RX with AM signal in the world on Perseus?"

Who knows. Very few people find it interesting or worthwhile to measure a radio's sensitivity. But then very few people own a signal generator which is what you need to do the job. Neither RF Space (SDR-IQ) nor Microtelecom (Perseus) have officially available AM sensitivity data. Instead they have MDS numbers for CW and SSB. The Perseus claims an MDS of -131 dBm in CW, 500 Hz bandwidth, and -124 dBm in SSB, 2.4 kHz bandwidth. Similar data for the SDR-IQ is -127 dBm in CW, 500 Hz bandwidth (no data given for SSB). So in theory (because I think these are calculated figures, not measured), 4 dB advantage Perseus.

There is no substitute for measurements though. I know of two AM sensitivity measurements on the SDR-IQ, mine and Dallas Lankford's. We both got -102 dBm or 1.8uV. Nico Palermo calculated the Perseus AM sensitivity for me to -102 dBm. A measurement will probably end up in that range, possibly 1-3 dB lower if my ears heard correctly. I believe that a correct Perseus sensitivity measurement will soon be done by Dallas Lankford.

Still, numbers, be they calculated or measured, will never replace real-world experience. I have yet to compare the two SDRs enough to declare a winner, and I'm not sure I want to put one ahead of the other anyway. It is highly unlikely that I will be able to hear a station on one radio that I can't hear on the other. That said, the Perseus appears to have AM bandwidth configuration options available that will dwarf most if not all other radios.

1 comment:

4nradio said...

Great comments on Perseus, Bjarne, and glad to hear you have one of these receivers now. It will be very interesting to see Dallas' findings on sensitivity, but as you've said the real world accomplishments down on the noise floor under actual conditions tell the true story. I'm anxious to get out to the WA coast (Grayland or Ocean City) with mine to use it under DXpedition conditions, but I won't be able to do that until the first week of January at the earliest.

When you mention the great bandwidth adjustments, are you referring to being able to "grab" the edge of the passband and shift and/or narrow it as desired? I like this too; it is one of my favorite features in PowerSDR for the SDR-1000. In particular I like using SAM mode and moving the passband to capture nearly all of the USB or LSB as desired. It seems to me this is the same as "Synchronous AM Selectable Sideband," like in some traditional receivers. Sure, you can tune LSB/USB to the Hertz (so-called ECSS tuning), but using SAM mode and offsetting the passband is quicker because you don't need to fuss with the exact tuning to get perfect zero-beat.

I too find the mouse scrollwheel motion for tuning to be reverse of what I expect, but that's a small complaint. A bigger issue is the operation of the slider...but I can't complain about now having 400 kHz recording available! The UTC time/date stamp is a big deal for me--I love it. I just wish I could see the time increment as I move the slider, such as with RecAll Pro.

I look forward to your other comments as you use Perseus further.

73, Guy Atkins