[time-nuts] Timing performance of servers

shalimr9 at gmail.com shalimr9 at gmail.com
Fri Oct 26 09:06:49 EDT 2012


If you cannot see the horizon because of obstructions (what else?), these obstructions are likely to be a source of multipath. So while technically you do not need to see the horizon, any obstruction above the horizon could cause problems. Of course, distant trees or a hill are less likely to be a problem than your neighbor's garden shed with a tin roof.

Also, some antennas are better at rejecting low angle signals than others. While the software can reject some undesired signals, it can only do so if the software can identify them as separate. If the multipath signal destructively interferes with the desired signal, there is not much the software can do.

Didier KO4BB


Sent from my Droid Razr 4G LTE wireless tracker.



-----Original Message-----
From: Rob Kimberley <robkimberley at btinternet.com>
To: 'Discussion of precise time and frequency measurement' <time-nuts at febo.com>
Sent: Thu, 25 Oct 2012 2:25 PM
Subject: Re: [time-nuts] Timing performance of servers

We used to filter out anything 10 - 20 degs above the horizon when setting
up timing receivers. Typically there's a lot of noise down low (multipath
and tropo effects). As long as you've got plenty of SVs you don't need to go
way down to the horizon.

Rob Kimberley

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Chris Albertson
Sent: 25 October 2012 20:09
To: lists at lazygranch.com; Discussion of precise time and frequency
measurement
Subject: Re: [time-nuts] Timing performance of servers

On Thu, Oct 25, 2012 at 11:02 AM,  <lists at lazygranch.com> wrote:
> The GPS seeing the horizon isn't required. Those satellites are filtered
out by software.

OK, technically it needs to see down to within 10 degrees of the
horizon.   But when you are choosing a location for the mast to the
horizon or withing 10 degrees of it looks pretty much the same.   I
don't want a huge tree of building due south of the antenna.  But for
timing all you really need is to see "most" of the sky.   It depends
on if you want it to work or work as well as it can.


Chris Albertson
Redondo Beach, California

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