# Linking Gnuradio and Gpredict? **URL:** \ **Category:** GNU Radio\ **Created:** [July 22, 2013, 1:33pm UTC](https://www.ruby-forum.com/t/linking-gnuradio-and-gpredict/245818 "2013-07-22T13:33:00Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\ **Post date:** [July 22, 2013, 1:33pm UTC](https://www.ruby-forum.com/t/linking-gnuradio-and-gpredict/245818/1 "2013-07-22T13:33:00Z")
Is it possible to link Gnuradio and Gpredict ? I want to use Gpredict as tracker controlling the antenna position and to pass doppler corrected frequency data to Gnuradio. Does any interface to Gpredict (or hamlib) exist ? thanks for any hints, Mark ---
**Author:** ![M\_Dammer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/3ab097/32.png) [@M\_Dammer](https://www.ruby-forum.com/u/M_Dammer)\ **Post date:** [July 22, 2013, 1:40pm UTC](https://www.ruby-forum.com/t/linking-gnuradio-and-gpredict/245818/2 "2013-07-22T13:40:01Z")
Hi, Gpredict is based on predict, which has several interfaces for Doppler prediction. Not sure if Gpredict inherited these interfaces. Yours Martin Am 22.07.2013 13:31, schrieb M Dammer: ---
**Author:** ![M\_Dammer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/3ab097/32.png) [@M\_Dammer](https://www.ruby-forum.com/u/M_Dammer)\ **Post date:** [March 28, 2014, 3:48pm UTC](https://www.ruby-forum.com/t/linking-gnuradio-and-gpredict/245818/3 "2014-03-28T15:48:49Z")
Hi, Can you explain in detail regarding querying the Gpredict for doppler corrected freq. using UDP, since I novice to UDP. If possible, can you please post the relevant code. Rajesh – View this message in context: [http://gnuradio.4.n7.nabble.com/linking-Gnuradio-and-Gpredict-tp42620p47286.html](http://gnuradio.4.n7.nabble.com/linking-Gnuradio-and-Gpredict-tp42620p47286.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![M\_Dammer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/3ab097/32.png) [@M\_Dammer](https://www.ruby-forum.com/u/M_Dammer)\ **Post date:** [July 22, 2013, 3:49pm UTC](https://www.ruby-forum.com/t/linking-gnuradio-and-gpredict/245818/4 "2013-07-22T15:49:08Z")
On 22/07/13 12:31, M Dammer wrote: > Is it possible to link Gnuradio and Gpredict ? I want to use Gpredict as > tracker controlling the antenna position and to pass doppler corrected > frequency data to Gnuradio. In a word, yes. Can be very simple. I did it by using an XML Server in the flow graph, and wrote a quick XML client (actually I “stole” most of it from an example), and sent the doppler info from predict via a variable. doppler info was received from predict using some code to query predict using UDP. I think I just used nc to send the UDP query to predict, recovered the shift from the reply, and sent it back to the XML Server running within the flow graph. Unfortunately I can’t find my actual code right now, but I literally copied an example, and added the UDP Predict clients bit. It went something like this pseudo code (Yes, this is a mix of shell,and python, and you need to re-write the getting doppler from predict yourself, but you get the idea, and should give you enough) import time import sys from socket import \* import xmlrpclib import binascii s = xmlrpclib.Server(“[http://192.168.39.74:8081](http://192.168.39.74:8081)”) infinite=1 while infinite == 1; # Grab predict doppler using UDP DOPPLER=`nc -u -s 2 $PREDICTHOST GET_DOPPLER $NORAD_NUMBER` s.set\_doppler\_shift($DOPPLER) time.sleep(1) The variable (lets call it doppler\_shift) exists in the flowgraph, and was multiplied appropriately and applied to the centre frequency of a FIR filter. You can pretty much pass any information you want in and out of a flow graph using a XML Server/Client pair. I’ve done TX/RX switching, and am currently working on telemetry decoding/display Iain ---
**Author:** ![M\_Dammer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/3ab097/32.png) [@M\_Dammer](https://www.ruby-forum.com/u/M_Dammer)\ **Post date:** [March 28, 2014, 6:34pm UTC](https://www.ruby-forum.com/t/linking-gnuradio-and-gpredict/245818/5 "2014-03-28T18:34:43Z")
I just found a good starting point. This program uses hamlib, a library that is often used to control rigs and antenna rotors and that is supported by GPredict: > **[Hamlib and SDR](http://james.ahlstrom.name/hamlib.html)** > > Hamlib and Software Defined Radio I just tested it and GPredict connects well to localhost:4575. The server programs output shows the proper doppler corrected frequencies etc. As it is python it can probably “converted” into a GRC block. 73 Mark ---
**Author:** ![M\_Dammer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/3ab097/32.png) [@M\_Dammer](https://www.ruby-forum.com/u/M_Dammer)\ **Post date:** [March 28, 2014, 7:36pm UTC](https://www.ruby-forum.com/t/linking-gnuradio-and-gpredict/245818/6 "2014-03-28T19:36:03Z")
If all you need is something in python you can just use pyephem [http://rhodesmill.org/pyephem/](http://rhodesmill.org/pyephem/) Alex