SDR# calibration (rtl2832)

[foxtail]

How do you folks calibrate your dongle? I see instructions to setup on noaa chl and move the freq. ppm from 0-?? depending on your dongle. What I want to know is how do I get it to match freqs. with a real scanner. I set the (pro-2026) scanner to 154.7550 and when I see it in sdr# and try to match it...the sdr# freqs. is 153.7020. Is this where the shift might come into play? Hoping someone can help with this. Thanks.

[mtindor]

I typically do this:

I move the red vertical line at the top of the FFT screen so that it matches the exact freq.

For instance, after I click "Play" [to start it], I'll set it so the freq says 162.550.000 (for the local NWS)

Then I'll click on "Configure" and start clicking the up/down arrows next to "Frequency correction (ppm)" until the actual signal lines up so that the red line is right in the middle of the peak of the signal [making sure the display still shows 162.550.000]. Once it lines up you should be good to go. Close the "Configure" screen. My particular DVB-T dongle requires a +17 ppm freq correction.

But you'll first want to make sure "Correct IQ" enabled in the main screen and also determine if you need to "Swap I & Q".

Mike

[foxtail]

What does the swap I & Q do? I had it checked so maybe I might be able to get it lined up without. ....Well, just un-cheked the swap i&q and the line is just off enough that the ppm will line up. Thanks for the help. P.S. is it unusual to have the ppm set as high as 89-90. The dongle has been plugged in for hours so it should be stable.

[kc0kp]

Originally Posted by foxtail

What does the swap I & Q do? I had it checked so maybe I might be able to get it lined up without. ....Well, just un-cheked the swap i&q and the line is just off enough that the ppm will line up. Thanks for the help. P.S. is it unusual to have the ppm set as high as 89-90. The dongle has been plugged in for hours so it should be stable.

Your number is not unreasonable. I have two of them, one is at +74 and the other at +56.
Since these things cost less than a TCXO for my FT857, accuracy and stability are a trade off.
Craig

[rbm]

I have five dongles and they run from from 12 to 77.

I just set it to a NOAA weather broadcast and set it to the center.

By the way, I have five different folders with SDR# (SDRSharp-1 through SDRSharp-5).
I have the dongles labeled to match so I don't have to keep retuning.
I also back up my frequency and config files so I don't lose them when I upgrade SDR#.

Rich