Re: [Discuss-gnuradio] linking Gnuradio and Gpredict ?

[Iain Young, G7III]

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";)
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