Frequency Correction

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ab5r

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I have now got my DVB-T+DAB+FM DONGLE and external antenna installed. My question is how to "zero-beat" the received frequency to correct for incorrect display?

I receive the NOAA WX station slightly off the proper assigned frequency. Is there a way to correct?

Thanks,
Jerry
 

rbm

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If you can receive any OTA digital TV channels you can use the following procedure.

The 'Frequency correction is the 'ppm' on the Configuration pop-up window.
It is used to correct the frequency variation of a particular dongle. (They all vary)

Typically, once it's set it doesn't vary much from day to day. But you must do it after the dongle has been powered on for a while.
Then, every time you start it up from cold, it will take a while to settle back down.

There are several ways to find that correction. (after about a 30 minute warm up).

The easiest way is to use the 'pilot' of an ATSC TV broadcast.

That is supposed to be 'exactly' 310 kHz within the TV signal. (ie. Channel 14 is at 470.310 MHz)
Using the highest frequency local channels works the best.

You can see a list of them here. Just check against a few local TV signals because they DO vary slightly.
North American television frequencies - Wikipedia, the free encyclopedia

Rich

Edit: This shows the view while calibrating to an ATSC TV pilot frequency.
Notice for best accuracy you need to zoom in.

 

rbm

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By the way, here's an example of what the dongle looks like from a cold start. ;)

Edit: Added a second screen capture of the same thing with a more recent version of SDR#

Rich




 
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ab5r

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Thanks, I'll try this. I should have mentioned that I am using HDDSR software. I had a problem getting SDR# installed.
 

tylerwatt12

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I would seriously consider raising the FFT resolution temporarily, during calibration. otherwise you'll get signals that are slightly "off" even though they look fine on the screen. This is especially important with narrowband transmissions.
 
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