[time-nuts] Purchasing a Trimble GPS timing solution
magnus at rubidium.dyndns.org
Sun Jul 12 21:46:41 UTC 2009
Chris Bridge wrote:
> Hi ,
> I was pointed to an Ebay seller who has an entire kit available (from
> China of course). Not knowing the product or pricing any better, can I
> get a comment on this link please?
> I hope I'm not breaking any rules here. I'm just trying to get the
> right thing at a half decent price. If the upcoming buy will include
> what I need, I can wait for it. I am worried about shipping and duty
> costs, UPS has proved to be a deadly foe in the past.
While that antenna isn't particularly good, it does get you up and
running and as a starters kit you are getting a good start with that
price. The Thunderbolts is a great start and probably suffice for many
people. I am about to give one away together with a pair of counters to
a friend in need. Should give him a flying start.
As for the antenna, there are two things which makes me object somewhat
to it. For one, the antenna has a bit short cable, so it prohibits you
from optimal placement. You would want as much unobstructed sky-view as
possible. The more horizon the better is the general rule. This allows
more sats and hence better geometries and better solution. This is more
important during surveying, but any errors built up during surveying of
position will crank out time-errors later. More sats also enables noise
and bias-sources to be reduced when time-navigation. The second
objection is that I think it can be a bit weak on the amplification,
which translates into problem with extending the cable.
Also, the magnet is intended for car use, and I have a similar antenna
on my car and it works fairly well for that task. It may not correlate
well with how you want to mount your antenna.
Don't get me wrong, it will work. It won't just be the best antenna in
the long run. The good thing is, you will be up and running. You can get
another antenna later and beef it up.
A few of us has large Choke ring antennas. They provide better
suppression of reflections and stable phase centers is usually
associated with that. Using such an antenna with a Thunderbolt will work
well, but is a bit over the top. Once the time-nut bug bites you hard,
you are down that trail yourself.
Then, next up is dual frequency receivers and antennas. Starts to be
meaningfull if you are running a Rubidium or better as your house-clock.
So, the link goes to what should be a great start-kit. All that you
need. Price is reasnoble IMHO. Can't recall that particular seller before.
More information about the time-nuts