Macro,

IMO the best way to track a satellite with any SDR is to apply the Doppler
correction to the NCO, I do this with ~ 10 updates / second when the
satellite is going overhead and the received beacon usually stays with 2Hz.

If you keep adjusting the center frequency you have to wait for changes to
take affect etc. If you use the NCO the change is immediate.

Simon Brown (G4ELI/HB9DRV)
http://v2.sdr-radio.com

From: USRP-users [mailto:usrp-users-bounces@lists.ettus.com] *On Behalf
Of *Marco Bosco
Sent: 25 January 2014 12:22
To: usrp-users@lists.ettus.com
Subject: [USRP-users] Doppler shift correction

Hi all!

This is my first time writing in this mailing list. I am using an USRPN210
with an SBX daughterboard as a transceiver for a satellite ground station.

I am trying to understand how to face the Doppler shift correction. Is it
better to implement a frequency estimator and set the USRP centre frequency
at the centre frequency of the satellite (radio amateur UHF band) or
changing the USRP centre frequency using the Doppler frequency correction
calculated from a satellite orbiter tracking software?

I am for the first solution but I would like to have other opinions.

Thanks,

Marco

USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

Marco,

If you are doing this with GNU Radio, you can probably leave the USRP
set at the nominal frequency, and correct doppler with a signal source
and mutlplier.  A simple app/custom block could query a program like
predict and update a doppler_frequency variable via XMLRPC.

Or there a number of similar approaches...

-John

Marco,

If you are doing this with GNU Radio, you can probably leave the USRP set at the nominal frequency, and correct doppler with a signal source and mutlplier.  A simple app/custom block could query a program like predict and update a doppler_frequency variable via XMLRPC.

Or there a number of similar approaches...

-John

On Sat, Jan 25, 2014 at 1:17 PM, Simon Brown <simon@sdr-radio.com mailto:simon@sdr-radio.com> wrote:

 Macro,

 IMO the best way to track a satellite with any SDR is to apply the Doppler correction to the NCO, I do this with ~ 10 updates / second when the satellite is going overhead and the received beacon usually stays with 2Hz.

 If you keep adjusting the center frequency you have to wait for changes to take affect etc. If you use the NCO the change is immediate.

 Simon Brown (G4ELI/HB9DRV)
 http://v2.sdr-radio.com

 *From:*USRP-users [mailto:usrp-users-bounces@lists.ettus.com <mailto:usrp-users-bounces@lists.ettus.com>] *On Behalf Of *Marco Bosco
 *Sent:* 25 January 2014 12:22
 *To:* usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>
 *Subject:* [USRP-users] Doppler shift correction

 Hi all!

 This is my first time writing in this mailing list. I am using an USRPN210 with an SBX daughterboard as a transceiver for a satellite ground station.

 I am trying to understand how to face the Doppler shift correction. Is it better to implement a frequency estimator and set the USRP centre frequency at the centre frequency of the satellite (radio amateur UHF band) or changing the USRP centre frequency using the Doppler frequency correction calculated from a satellite orbiter tracking software?

 I am for the first solution but I would like to have other opinions.

 Thanks,

 Marco


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 USRP-users mailing list
 USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com>
 http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

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USRP-users@lists.ettus.com
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Thanks for your suggestions.

Does anyone can suggest a simple way to get the Doppler shift
frequency calculated by a satellite tracker software (e.g. Gpredict)
and pass it to GNURadio? I found this
https://github.com/darkstar007/GroundStation but I am wondering if
there are other solutions.

BTW using Hamlib with Gpredict, it is very easy to tune analog radio
but USRP is not supported, if I am correct.

Marco

**

Thanks for your suggestions.

Does anyone can suggest a simple way to get the Doppler shift
frequency calculated by a satellite tracker software (e.g. Gpredict)
and pass it to GNURadio? I found this
https://github.com/darkstar007/GroundStation but I am wondering if
there are other solutions.

BTW using Hamlib with Gpredict, it is very easy to tune analog radio
but USRP is not supported, if I am correct.

Marco

From: USRP-users [mailto:usrp-users-bounces@lists.ettus.com] On Behalf
Of Marcus Müller
Sent: domenica 26 gennaio 2014 19.44
To: usrp-users@lists.ettus.com
Subject: Re: [USRP-users] Doppler shift correction

Hi Marco,

assuming that during observable movement the desired bandwidth stays
within the boundaries of your USRP's center frequency +- f_sample/2,
as Simon said, you could go the pure software-based approach of
frequency correction on the host.
To answer your question on how to tune: The tuner on the SBX has a
granulartity; it can't physically produce all real frequencies in the
target band.
If you tune to a frequency that is not available to the oscillator,
UHD chooses a suitable frequency in the vicinity of the target
frequency and digitally mixes the signal down to shift it by the
remaining frequency offset.

If you (as in case with sattelites) are able to predict the frequency
shift exactly, you can of course use the suggested means of correction
using variable frequency mixing.
For the sake of generality, inaccurate local oscillators etc, you
could also consider a frequency correction feedback loop as supplied
e.g in gr::analog::pll_carriertracking_cc;
that is basically going your second proposed way of estimating a
frequency error and shifting the signal accordingly, but in software
instead of in hardware.

Greetings,
Marcus

On 01/25/2014 10:27 PM, John Malsbury wrote:

     Marco,
     
     
     
     If you are doing this with GNU Radio, you can probably leave
     the USRP set at the nominal frequency, and correct doppler
     with a signal source and mutlplier.  A simple app/custom block
     could query a program like predict and update a
     doppler_frequency variable via XMLRPC.  
     
     
     Or there a number of similar approaches...
     
     
      
     
     
     
     -John
     
     
      
     
     
     On Sat, Jan 25, 2014 at 1:17 PM, Simon Brown
     <simon@sdr-radio.com> wrote:
     
     
             Macro,
             
              
             
             IMO the best way to track a satellite with any SDR is
             to apply the Doppler correction to the NCO, I do this
             with ~ 10 updates / second when the satellite is going
             overhead and the received beacon usually stays with
             2Hz.
             
              
             
             If you keep adjusting the center frequency you have to
             wait for changes to take affect etc. If you use the
             NCO the change is immediate.
             
              
             
             
             Simon Brown (G4ELI/HB9DRV)
             http://v2.sdr-radio.com
             
             
             
              
             
             
             From: USRP-users
             [mailto:usrp-users-bounces@lists.ettus.com] On Behalf
             Of Marco Bosco
             Sent: 25 January 2014 12:22
             To: usrp-users@lists.ettus.com
             Subject: [USRP-users] Doppler shift correction
             
             
              
             
             Hi all!
             
              
             
             This is my first time writing in this mailing list. I
             am using an USRPN210 with an SBX daughterboard as a
             transceiver for a satellite ground station.
             
             I am trying to understand how to face the Doppler
             shift correction. Is it better to implement a
             frequency estimator and set the USRP centre frequency
             at the centre frequency of the satellite (radio
             amateur UHF band) or changing the USRP centre
             frequency using the Doppler frequency correction
             calculated from a satellite orbiter tracking software?
             
             I am for the first solution but I would like to have
             other opinions.
             
              
             
             Thanks,
             
              
             
             Marco
             
              
             
             
             
             
             _______________________________________________
             USRP-users mailing list
             USRP-users@lists.ettus.com
             http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
             
     
      
     
     
     
     
     
     
     
     _______________________________________________
     USRP-users mailing list
     USRP-users@lists.ettus.com
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USRP-users mailing list
USRP-users@lists.ettus.com
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You can find in the predict library how it is calculated (gpredict use
it also)
http://www.qsl.net/kd2bd/predict.html

A snip how use it, satellite elevation (over the station), -range and
-range-rate must be known:

if(sat_ele >= 0.0) {
dl = atof(downlink.c_str()); // MHz
doppler100 = -100.0e06*((sat_range_rate1000.0)/299792458.0);
delay = 1000.0((1000.0*sat_range)/299792458.0);

  if(dl != 0.0) {
     dopp = 1.0e-08*(doppler100*dl);
     loss = 32.4+(20.0*log10(dl))+(20.0*log10(sat_range));
     sat_rx = dl + dopp;

     str_doppler.printf("RX:%.*f MHz Pathloss:%.3f dB Delay:%.3f ms",
     downlink.Length()-4, sat_rx, loss, delay);
  }

  if(fabs(sat_range_rate) < 0.1) // Time of Closest Approach
     str_status.printf("%s TCA", mode&1 ? "Recording":"Tracking");
  else if(sat_range_rate < 0.0)  // Approaching
     str_status.printf("%s approaching", mode&1 ? 

"Recording":"Tracking");
else // if(sat_range_rate > 0.0) // Receding
str_status.printf("%s receding", mode&1 ?
"Recording":"Tracking");
}

Patrik
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com