[time-nuts] GPS Antenna
dave.martindale at gmail.com
Mon Sep 12 17:13:04 UTC 2011
In theory at least, a single satellite is enough to provide timing in
position hold mode.
However, that assumes you get a direct line-of-sight signal, with no
multipath. A reflected signal has additional delay that the GPS
receiver cannot factor out if it's receiving only one satellite. If
it is receiving many, it *might* be able to tell which ones have
multipath delays and ignore them.
A high antenna tends to have good line-of-sight reception of the
satellites, as well as receiving more of them. The former might be
more important than the latter.
2011/9/12 Miguel Gonçalves <mail at miguelgoncalves.com>:
> Hi Chris!
> Here and on ntp-questions always helping me out! Thanks!
> Moving it up to the roof would be difficult. Would have to talk to all
> neighbours to ask permission to run a cable to the roof. I'll have to keep
> it at this location.
> Anyway, in position hold I would assume that using 2 satellites will give me
> good time. Right?
> Thanks again!
> On 12 September 2011 16:03, Chris Albertson <albertson.chris at gmail.com>wrote:
>> 2011/9/12 Miguel Gonçalves <mail at miguelgoncalves.com>:..
>> > oncore# /var/tmp/sats.sh
>> > 8 satellites: 0
>> > 7 satellites: 0
>> > 6 satellites: 870
>> > 5 satellites: 7941
>> > 4 satellites: 7313
>> > 3 satellites: 6385
>> > 2 satellites: 575
>> > 1 satellites: 0
>> > The machine has been running for 6 hours and it has been seeing a good
>> > number of satellites for most of the time.
>> > Do you think I should buy an external antenna .....
>> It looks like your current antenna can only see about 1/2 of the sky.
>> The reason to replace it is so you can see the entire sky. the
>> Panasonic would be ideal because it has enough gain to drive a long
>> cable. THere is no resin to replace the antenna unless you intend
>> to place it in a better location. A higher gain at the same
>> location will not give you a better view of the sky.
>> Any outdoor antenna needs to be pointed or have a dome shape so that
>> whatever falls on it rolls off.
>> Chris Albertson
>> Redondo Beach, California
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