[time-nuts] Surplus carrier phase measurement-capable receivers

bg at lysator.liu.se bg at lysator.liu.se
Mon Jul 13 09:29:38 UTC 2009


> The main problem is a standard L1 frequency only receiver is not much
> better than a plain jane receiver when Selective Availability is turned
> off (and particularly is WAAS corrections are available).  This is the
> standard operating mode of GPS today.   Choke ring antennas, etc are
> fairly useless overkill in this application.

An L1/L2 receiver is also not much better than your modern car GPS in
standalone operation.

> To get any kind of real accuracy out of an L1 only receiver requires two
> receivers with one set up at a precisely known point.  I have a three unit
> Ashtech Locus surveying system that is L1 only.  The NGS is working on a
> version of their OPUS post-processing system for L1 only receivers.  It
> remains to be seen what kind of accuracy one can get with a single L1
> carrier phase receiver.

There is no conceptual difference between using L1 and dual freq
receivers. You still compare your measurements to a stationary reference
receivers. The difference is that dual freq receivers can have a lot
longer distances between the receivers and get a "sub dm"-level accuracy.

> For any serious accuracy you need an L1/L2 receiver that can track both
> carriers so you can do proper ionospheric corrections.  These puppies will
> set you back around $10,000-$50,000 dollars.

You can get a good new receiver for sub $4k.

   http://www.javad.com/cgi-bin/jgnss/cgi?Action=Buy&ProductID=663

A good antenna can be had for sub $1k, if you look around a little.

> Your best bet is to probably find an Ashtech Z12 unit.  These were state
> of the art around 15 years ago and are still hard to beat.  With luck you
> can score one for around $1000...  make sure it comes with a proper L1/L2
> antenna.  A replacement antenna will cost at least that much.

Z12 is a good recomendation, but be aware that they contain old
electronics that might start to fail. Many sellers are can not or will not
show you pictures of the receiver running. Thus you might be buying an
expensive paperweight. You might also need to replace internal memory
backup batteries, to get them to work. Besides a dual freq antenna you
should also make sure you get power and serial cables. They are avalable
for purchase but will set you back another ca $300...

--

   Björn





More information about the Time-nuts_lists.febo.com mailing list