[time-nuts] How to tell a "survey grade" antenna

[Lux, Jim (337C)]

On 8/14/09 9:01 AM, "John Green" <wpxs472 at gmail.com> wrote:

> Thanks guys. I bookmarked that site. I don't know that I'll be able to find
> one but at least I know what to look for now.
> 

You may not have an exact match, but they've got tons of data on other
models there, and, it at least gives you somewhere to start.

The unavco.org site has a report with the actual dimensions of several mfrs
choke rings.

There's not a huge difference among the various antennas, from what I can
see. Mostly it's small details probably driven by that company's particular
manufacturing processes. Maybe the mounting bracket on the bottom matches
their tripods or supports, or the slot/rib dimensions are what they've found
works.  I wouldn't even be surprised if they just happen to match the first
prototype they built. "It works 'good enough' and we've got the G-code
programming for the CNC mill, so why change"

There might also be patent issues forcing small differences (e.g. Dual band,
or conical, or dielectric loading of the slots)

I would think that the original JPL design might be freely manufacturable,
if you were to find a suitable company that can do the machining for you. Or
if you had a big lathe or a mill with a rotary table.



And, of course, you could always calibrate/measure your own antenna. Larry
Young and Charley Dunn did tons of these measurements at JPL at least 10
years ago, and I think they used a modified version of the Rogue receiver
and just recorded a bunch of data as the s/v's went overhead, and then post
processed it.   Actually, someone at JPL is still doing those kinds of
measurements, because you always see some different kind of antenna sticking
up from the building where the GPS guys and gals are. Why yes, there is
GPS-precision-nuttery as well as time-nuttery, and some folks get to do it
as part of their job. Larry and Charley have moved up in the hierarchy, so I
doubt they're out standing next to the antenna on the range, but you never
know...  

In any case, if anyone's interested, I can probably dig up the relevant
papers and reports on how to do it.