[time-nuts] BPSK Receiver & GPS Antenna siting

[johncroos at aol.com]

Various comments -

Hal mentioned SNR for the scheme I suggested. A PLL can be a coherent 
demodulator of arbitrary
bandwidth. Thus the PLL at the output of the doubler can have a small 
bandwidth since at that point
there is no PSK, it having been removed by the doubler. So given a 
stable VCXO you can probably get down
to 1 Hz and thereby achieve a good SNR. There is a lot of stuff out 
there on phase tracking receivers
that do exactly that. You know the frequency so the loop does not have 
to search far and the BW can be increased
for acquisition and closed up for tracking.

On writing reams of code - my point was that it is not required to used 
the admittedly more powerful software
techniques to do this job - I noted that one reason to write reams of 
code is for the fun of it, this is after all
a hobby.

GPS Antenna Siting -

Lets not make this so hard. Mine is at 6 ft elevation and is blocked to 
an elevation angle of 20 to 30 degrees by a house
within 15 ft and a forest of trees. I have room and no restrictions but 
I also have severe thunderstorms - so the house
plays lightning protect for the antenna. My T bolt tracks a Rb to 
better than 1e-12 over 24  hours with no serious 10 MHz phase bumps
as plotted on a  strip chart recorder.

Sooooo  -

Put your antenna at 6 ft in back yard. Start out on a photo tripod - 
who is gonna notice?
set up a t bolt at EL=5 AMU=0 Damping = 1.2 and Time Constant = 100 sec.
get the t bolt manual
get Tbolt monitor
get Lady Heather and read all that stuff.

Run Lady Heather antenna survey (command SAS)  for at least two days - 
you get a map of signal level in dBc vs elevation
Reset the Tbolt elevation mask to reject anything that is shown as 
blocked using the signal
level map. Likewise experiment with the AMU setting to reject the weak 
= poor signals. Mine works good
with AMU all the way up to 10 as fewer good satellites are better than 
lots of weak ones.

The satellites are in high orbits so masking those below 25 degrees is 
OK and the AMU sets the acceptable signal
level - at AMU 10 my setup throws out those below about 40 dBc - the 
strong guys go up to 50. This is a function
of you antenna performance so some experimentation is required.

-73 john k6iql