doppler.py

#!/usr/bin/env python2

import ephem
import socket
import sys
from contextlib import contextmanager
from time import gmtime, strftime

C = 300000000.
F0 = 137900000.
LATITUDE = '41.0000'    # changeme (degrees)
LONGITUDE = '-91.0000'  # changeme (degrees)
ALTITUDE = 100          # changeme (meters)
TLEFILE = '/home/user/tlefile.tle'


@contextmanager
def socketcontext(*args, **kwargs):
    s = socket.socket(*args, **kwargs)
    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    s.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
    yield s
    s.close()

with open(TLEFILE, 'r') as f:
    data = f.readlines()

myloc = ephem.Observer()
myloc.lon = LONGITUDE
myloc.lat = LATITUDE
myloc.elevation = ALTITUDE

mysat = ephem.readtle(data[0], data[1], data[2])

def dopplercalc():
    myloc.date = strftime('%Y/%m/%d %H:%M:%S', gmtime())
    mysat.compute(myloc)
    doppler = int(F0 - mysat.range_velocity * F0 / C)
    return doppler

try:
    with socketcontext(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.connect(('localhost', 4532))
        doppler = F0
        while True:
            new_doppler = dopplercalc()
            if new_doppler != doppler:
                s.send('F' + str(new_doppler) + '\n')
            doppler = new_doppler
except socket.error:
    sys.exit()