Hi Wolfgang,
You Wrote:
On 01/08/15 09:17, Wolfgang Nagele wrote:
Hi,
I've recently needed to correct some satellite signals for Doppler
shift. I found that there was no easy way to do this yet - so I've
Interesting. The way I did it was the following (using predict, rather
than gpredict):
a) Add a XMLRPC Server block to my flowgraph
b) Write a piece of python glue code which:
i) Gets the normalised doppler info from predict via UDP 1210
ii) Calculates the correct doppler for the s/c frequency
iii) Sends it onto gnuradio to set a variable, which twiddles
a FIR filter by the correct amount rather than mixing via a multiply
block.
Here is a version of the whole thing used for tracking Funcube-1
aka AO-73. I use similar scripts for doppler correcting the NOAA birds
as well, and do have a version which handles multiple spacecraft on one
flowgraph
#!/usr/bin/env python
import sys
import time
import socket
import xmlrpclib
# Create UDP Socket
predsock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
# Create XML Object
s = xmlrpclib.Server("http://localhost:8080";);
# Get Satellite object or name
s_c = str(sys.argv[1]);
doppler_msg = "GET_DOPPLER " + s_c
while True:
# Get Doppler from Predict
predsock.sendto(doppler_msg , ("127.0.0.1",1210))
doppler_str,predaddr = predsock.recvfrom(24)
# Adjust for correct frequency
dopp_float = float(doppler_str)
dopp_freq = (145.935/100.000)*dopp_float
print dopp_freq , dopp_float
# Send to grc
try:
s.set_dopp_freq(dopp_freq)
except socket.error:
pass
# Sleep
time.sleep(1)
All the Best
Iain
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