RSP2 Frequency is Incorrect

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ultravista
Posts: 17
Joined: Thu Jun 22, 2017 3:40 pm

RSP2 Frequency is Incorrect

Postby ultravista » Fri Jul 21, 2017 1:37 am

I just bought a 2nd hand RSP 2 on eBay (from a HAM operator).

With SDRUno, SDR#, and HDSDR, the frequency is off a bit compared to a known signal. For example, in SDRuno, my local Las Vegas WWV frequency is 162.555.000 but the applications above don't 'center' with the signal @ 162.555.000 but 162.555.200 instead.

By 'center', I mean the peak of the signal in the application.

The issue is similar across every application, so I know it's not an offset problem with a single application.

For the record, my RTL-SDR v1.3 dongle tunes exactly on the right frequency.

What would cause the RSP 2 to tune incorrectly?

Also, to address the problem correctly, what are the last three digits of the frequency - 162.555.200 - the .200 in this set?

Is it hertz?

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ultravista
Posts: 17
Joined: Thu Jun 22, 2017 3:40 pm

Re: RSP2 Frequency is Incorrect

Postby ultravista » Fri Jul 21, 2017 3:46 am

Correction - NOAA weather. I cannot edit ...

Would calibration address the problem and if so, must it be done with every application?

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dlritter
Posts: 27
Joined: Fri Dec 04, 2015 7:12 pm

Re: RSP2 Frequency is Incorrect

Postby dlritter » Fri Jul 21, 2017 3:02 pm

First, according to NOAA data base the 7 assigned NOAA channels are:
162.400
162.425
162.450
162.475
162.500
162.525
162.550
Now your stations transmitter might be a bit out of maintenance window and a little high i frequency.. but I would tend to think not.
You have a single receiver sample, your only RSP2. I would not say these are precision devices, which is why the RSP2 pro was created to support external frequency standard input from a GPSDO or other standard such as the Leo Bodner GPSDO from airspy.us for 199.
That being said, just accomplish a PPM offset adjustment..
Open the SDRuno RX windows, select the Sett. button and scroll tab list over to Cal and select.. I think it is effective for each VRX..
follow displayed instructions and have fun..
773 Dave N6DL

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vk3alb
Posts: 19
Joined: Sat Jul 01, 2017 11:43 pm

Re: RSP2 Frequency is Incorrect

Postby vk3alb » Fri Jul 21, 2017 10:40 pm

ultravista wrote:Asked a couple of questions

Would calibration address the problem and if so, must it be done with every application?

Also, to address the problem correctly, what are the last three digits of the frequency - 162.555.200 - the .200 in this set?



1) Yes, calibration will address the frequency accuracy problem.

However, if I were you I would first check more than one known frequency before you determine that your RSP2 is off. Once you are sure then go ahead and do the calibration. I believe you will need to do this calibration for each software package you use.

2) Yes the 200 indicates 200Hz.

My personal opinion

You are using at least 3 different software packages with your RSP2. I think it would be interesting to try the calibration with one software package and see what you get in the other two. Do they interact?

Read up on the software and understand the calibration process in each package. There is usually a way to get back to factory defaults. If not, take a note of your current calibration value so you can restore it if you get unexpected results.

The fun of all this is you can experiment and learn without breaking anything - enjoy.
Last edited by vk3alb on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Lou
VK3ALB

Tech_Support
Posts: 240
Joined: Mon Jun 01, 2015 7:00 pm

Re: RSP2 Frequency is Incorrect

Postby Tech_Support » Sat Jul 22, 2017 4:40 pm

The RSP2 is fitted with a 0.5ppm TCXO and so it should be pretty accurate. Broadcast stations frequencies are not necessarily particularly accurate though, so I would double check against a known precision station such as WWV using the highest frequency that you can find.

FWIW, it is perfectly possibly to get a device with a specified 20 ppm Xtal that will be spot on in frequency. The tolerance is the maximum specified error and not the error itself. The original RSP1 was fitted with a 10ppm Xtal, but many people found the frequency error to be 1ppm or less. It just isn't guaranteed to be so.

Frequency errors can be reduced by calibration and it should be possible to calibrate down to an initial error of around 0.01 ppm. SDRuno has a specific mode for calibrating against a known precision frequency. Please note that this will not necessarily remain this accurate if the temperature varies.

Once correctly calibrated in SDRuno, the calibration will hold good at all frequencies. Each application will need individually calibrating though as the calibration settings are stored in the application. Having calibrated in SDRuno. it is possible to make a note of the frequency correction and simply use that value in other applications.

Sincerely

SDRplay Tech_Support

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