Alternate SDR Dongle Frequency Calibration Reference

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jonwienke

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You can use this with the default antenna supplied with most of the cheap dongles.

The GPS L4 signal shows up as a visible spike at 1379.913MHz. The bandwidth in that area is uncluttered, to prevent interference with GPS signals. If using SDR#, enable the IF display window to get a close-up view of the spectrum. Adjust the PPM setting to align the spike as close as possible to 1379.913MHz. It's pretty easy to get an alignment to the nearest PPM, which is close enough for pretty much anything.

It's easier to get an accurate calibration with this reference than using TV stations or other lower-frequency broadcasts.
 

SRSP2282

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Interesting. Ill have to give this a go next time I calibrate. I have been using the NOAA WX stations with good results, but Im always down to try something new. Thanks for the suggestion.
 

rbm

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I may be missing something here.

Exactly where do you see a spike at 1379.913 MHz?
It's not at all visible here in upstate NY.

Rich

GPS L4 1379.913 MHz
 
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SCPD

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I didn't see anything in that range either.

jonwienke - do you have an R820T or an E4000 tuner?
 

BM82557

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In - Global Positioning System - Wikipedia, the free encyclopedia the freqs are listed as ---


L1 1575.42 MHz Coarse-acquisition (C/A) and encrypted precision (P(Y)) codes, plus the L1 civilian (L1C) and military (M) codes on future Block III satellites.
L2 1227.60 MHz P(Y) code, plus the L2C and military codes on the Block IIR-M and newer satellites.
L3 1381.05 MHz Used for nuclear detonation (NUDET) detection.
L4 1379.913 MHz Being studied for additional ionospheric correction.[citation needed]
L5 1176.45 MHz Proposed for use as a civilian safety-of-life (SoL) signal.
 

jonwienke

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Evidently it's not broadcast constantly, or only by some satellites. It's there sometimes, but not all the time. Which diminishes its usefulness as a calibration reference.
 

Flatliner

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I don't see the signal either, but I thought that it's just not penetrating the roof, though I can use GPS inside without an issue usually.
 

rbm

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Forgot that my antenna has a range of 25 - 1300 Mhz.
So does mine ...... (With a ZQL-1900MLN preamp right at the antenna and a ZQL-1900LNW inside)

I can see aircraft (1090 MHz ADS-B) signals out to around 125 miles before the hills shade the horizon.

But, I see no spike at 1379.913 MHz.

Rich

ADS-B @ 1090 MHz:

 

jonwienke

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jonwienke - do you have an R820T or an E4000 tuner?
I have a R820T. I've checked a few times, and haven't seen the L4 signal lately. I'll check again when I get home from work tonight.

If it was broadcast continuously, it would make a great calibration reference, but if not, it's not very useful.
 

WayneH

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I wish that you'd make up your bleedin' mind. You sound like my wife!
I agree. We don't need a blow by blow. Since it's a trial expect it to go up and down.

Or just manually tune what you're listening to on the fly. It's LMR and not every transmitter is going to be calibrated perfectly. Not to mention the osc is going to drift in these dongles anyway. I've adjusted to a calibrated service monitor and it still doesn't make a difference if the dongle ambient fluctuates.
 

rbm

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Why chase after the 'holy grail' of calibration when the 'pilot' of an ATSC TV broadcast is accurate enough?

I normally compare around 7 pilots and the most my calibration varies between all of them is 1 ppm. (with 12 dongles)
Granted, some technicians are sloppy but there's nothing magical about it.

It you can't receive any TV signals, that would be a problem.

And there are other ways to do it.
Kalibrate (kal.exe is) one.
It uses any GSM signal to calculate ppm for you.
I used that a long time ago. Kalibrate-RTL: Calibrate #SDR (SDR Sharp) Linux/Windows TUTORIAL. | RTL-SDR.Sceners.ORG

But it's a pain compared to just sticking the pilot frequencies in 'Frequency Manager' and checking it once in a while.

I've never found + or - 1 ppm to prevent me from decoding any digital formats.

In any case, you can increase the bandwidth slightly to make up for any calibration error.

Rich
 
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