[time-nuts] BPSK Receiver & GPS Antenna siting

Bob Camp lists at rtty.us
Thu Sep 27 23:20:14 UTC 2012


Hi

At least in my back yard, a 6' tall tripod would be very noticeable from a number of directions. There are many others in similar situations. If I were to interpret the restrictions literally as written, an antenna that was inside the house, but visible through an open window is also a violation.

Bob


On Sep 27, 2012, at 7:11 PM, johncroos at aol.com wrote:

> 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
> 
> 
> 
> 
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