[time-nuts] Difference in GPS antennas

Joseph M Gwinn gwinn at raytheon.com
Fri Aug 14 19:21:48 UTC 2009


Bob,


time-nuts-bounces at febo.com wrote on 08/14/2009 01:05:34 PM:

> From:
> 
> Robert Darlington <rdarlington at gmail.com>
> 
> To:
> 
> Discussion of precise time and frequency measurement 
<time-nuts at febo.com>
> 
> Date:
> 
> 08/14/2009 02:06 PM
> 
> Subject:
> 
> Re: [time-nuts] Difference in GPS antennas
> 
> Sent by:
> 
> time-nuts-bounces at febo.com
> 
> Hrm, I'm looking for a sheet of Eccosorb to make an anechoic chamber (a 
very
> small one) for testing 2.4GHz printed (PCB) antennas.  I'd be interested 
in
> knowing the specs.   The idea with what I'm doing is that I cansweep the
> antenna with the network analyzer and still be near the antenna to keep 
the
> cables short, while at the same time not interfere with the 
measurements.  I
> met a guy from Microchip last week that showed me what he was doing and 
what
> works well for him.  He built a box about 8" high and about 5 inch 
square on
> the bottom (inside dimensions).  Even though it's pretty parallel on the
> inside, reflection is a minimum because of the material.

The main advice I would give is to make sure the box isn't perfectly 
square or rectangular, so standing waves cannot form.

So, build it sloppy, with walls visibly askew (not perpendicular to one 
another).

Joe Gwinn


> On Fri, Aug 14, 2009 at 10:46 AM, Pete Lancashire
> <pete at petelancashire.com>wrote:
> 
> > I have some (well a LOT) of microwave absorber. it looks
> > like a mix of ferrite and rubber that has been bonded
> > to a stainless steel cloth (think window screening) in the
> > middle. About 1/8" thick.
> >
> > I can get the make, p/n and a picture this weekend if interested.
> > I remember the company that made it got bought out, which then
> > got bought out etc and I gave up.
> >
> > Price would be free+shipping, there are about 400 each
> > sheets about 30x30 inches. Each sheet must weight 5 lbs.
> >
> >
> > >
> > >
> > > On 8/14/09 9:13 AM, "Mark Sims" <holrum at hotmail.com> wrote:
> > >
> > >>
> > >
> > >>
> > >> Some of the data collection runs that I want to do is withthe patch
> > >> mounted
> > >> on a pizza pan and in a cake pan and see if that helps the
> performance
> > >> by
> > >> faking what a survey antenna does.
> > >>
> > >
> > > If you can scrounge up some suitable RF absorbing material 
> to put on the
> > > pan, that might be an interesting experiment.  Maybe even 
> something like
> > > charcoal briquettes (I don't know if the resistivity is right..)
> > >
> > >
> > >
> > > I've tried the pizza pan thing, but that was because my antenna was 
a
> > > magmount, and it was convenient. I didn't see if it gave better
> > > performance.
> > > A flat plate might actually be worse than putting the bare 
> antenna up on
> > a
> > > pole, because it gives strong multipath from a very close reflection
> > > point.
> > >
> > >
> > > _______________________________________________
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> > > To unsubscribe, go to
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> > > and follow the instructions there.
> > >




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