Calibration Using CHU

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VE9DAN
Posts: 15
Joined: Tue Jul 31, 2018 12:08 pm

Calibration Using CHU

Postby VE9DAN » Sun Jun 09, 2019 9:13 pm

Please have a look at the attached screenshot from my spectrum analyzer. Version 1.0
I am measuring the two frequencies transmitted by CHU. One is the carrier freq of 7.850 and I am reading it 6 Hz lower than I should be.
The second freq CHU transmits are the beeps and they set it 1,000 Hz higher. I am reading it 7 Hz higher than I should be.

So basically my SDRplay receiver is 6 Hz LOW (which is fine ... I can deal with that).

Here is the problem ... a mere 1,000 Hz away, the SDRplay reads 7 Hz HIGH.

How can this be ???

Ooops ... I tried to paste the Screenshot but can't. But the numbers speak for themselves. Try this yourselves and see what you get for peak frequencies.
I also found that if I play around with the ppm setting, I can never get the Analyzer to be dead on.

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Mike2459
Posts: 278
Joined: Mon Jul 24, 2017 8:24 pm

Re: Calibration Using CHU

Postby Mike2459 » Mon Jun 10, 2019 1:23 am

They look pretty close on mine:

SA10.JPG
SA10.JPG (213.37 KiB) Viewed 323 times

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Mike2459
Posts: 278
Joined: Mon Jul 24, 2017 8:24 pm

Re: Calibration Using CHU

Postby Mike2459 » Mon Jun 10, 2019 1:43 am

Let's try that again with some markers!

Capture.JPG
Capture.JPG (111.68 KiB) Viewed 319 times

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VE9DAN
Posts: 15
Joined: Tue Jul 31, 2018 12:08 pm

Re: Calibration Using CHU

Postby VE9DAN » Mon Jun 10, 2019 7:01 am

Very good. You have to explain to me how you were able to post the screenshots.

I see you are 2 Hz low on the carrier, and 3 Hz low on the beeps.

Can you please try using the ppm setting on the lower right hand side of the screen to adjust the marker frequencies ... just to see if you can get the two frequencies accurate.

Secondly, can you try it with a 10 KHz span.

I am using the RSP 1. What model are you using?

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Mike2459
Posts: 278
Joined: Mon Jul 24, 2017 8:24 pm

Re: Calibration Using CHU

Postby Mike2459 » Mon Jun 10, 2019 5:09 pm

I use Windows Snip Tool for captures. Click on the 'attachments' tab - there will be a choice to 'add files'. 'Place inline' will appear after the file is uploaded. Make sure your blinking text 'cursor' is where you want it because that's where the image will be placed in the body of the message. Clicking 'Place Inline' inserts the image file into the message body.




They way I did it:

Set PPM first:
Span 1 kHz
Centre Frequency 7.850000 or 3.330000 - I used 7.85, 3.33 was nil heard
Trace select set to Raw
Sweeps: 2
NFFT: 524288
Place marker A at the carrier frequency in the spectrum analyzer's window
Slowly adjust PPM until the carrier is centered on the peak of CHU's carrier, it was -0.5 on my RSP2.


Tune the SA to CHU's 1 kHz tone by setting SA's Centre Freq to 7.851000. Place a 2nd marker B at 7.85100
In my case Marker A - Marker B was -0.001001 mHz (we've got a small error already!)

Now, set the center freq to 7.850500, span to 2 kHz (to see both markers). In my case marker B is now showing 7.850999. If you toggle between 2 khz span and 1 khz span you will 'lose' 1 Hz on each change at Marker B. You can readjust Marker A and B to the correct frequency easily at 2 kHz Span, it's next to impossible when the span is at 10 kHz.

2 khz span.JPG
2 khz span.JPG (165.32 KiB) Viewed 250 times


Note how the marker frequencies change when span is changed.


10 khz span.JPG
10 khz span.JPG (154.63 KiB) Viewed 250 times




Honestly, I don't think this program was designed with this use in mind. It works well for it's intended purpose, however.

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VE9DAN
Posts: 15
Joined: Tue Jul 31, 2018 12:08 pm

Re: Calibration Using CHU

Postby VE9DAN » Mon Jun 10, 2019 6:42 pm

Yes Mike, I see what you are doing.
I'll play with it tonight and get back to you.
Dan

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