Tom,

On 04/17/2013 07:21 AM, Tom Van Baak wrote:

OK, now you start to make sense ;-)

Only #2 should be a challenge, as #1 and #3 has buffered output. Still,
you want some buffering. A suitable CMOS gate should pull it off.
Otherwise a FET-probe to a PSU and then into the TimePod should do the
trick.

Cheers,
Magnus

Another way to ask this question is "what is the effect of a small
deviation form the ideal dimensions?"

If we assume deviations of about 1/20th of a wavelength are OK then we can
allow about 1cm of dimensional error.  Almost anyone using simple hand
tools can do better.

With care using primitive "garage" equipment we can do much better.  The
old-school hand method for precision sheet metal work was to make a
hardwood form and then bend and cut the metal around the wood form.

I think if a cake pan would work is a matter of luck.  You'd just have to
find one within about 2cm of the correct diameter.  If not then you be
better off starting with flat sheet and hand shears.

On Tue, Apr 16, 2013 at 10:46 PM, David J Taylor <
david-taylor@blueyonder.co.uk> wrote:

--

Chris Albertson
Redondo Beach, California

But the pan is just a ground plane. It isn't a reflector based on the type of antennas I saw in the photograph.

Sent via BlackBerry from T-Mobile

-----Original Message-----
From: Chris Albertson albertson.chris@gmail.com
Sender: time-nuts-bounces@febo.com
Date: Wed, 17 Apr 2013 12:18:00
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] antennas was Re: Common-View GPS Network

Another way to ask this question is "what is the effect of a small
deviation form the ideal dimensions?"

If we assume deviations of about 1/20th of a wavelength are OK then we can
allow about 1cm of dimensional error.  Almost anyone using simple hand
tools can do better.

With care using primitive "garage" equipment we can do much better.  The
old-school hand method for precision sheet metal work was to make a
hardwood form and then bend and cut the metal around the wood form.

I think if a cake pan would work is a matter of luck.  You'd just have to
find one within about 2cm of the correct diameter.  If not then you be
better off starting with flat sheet and hand shears.

On Tue, Apr 16, 2013 at 10:46 PM, David J Taylor <
david-taylor@blueyonder.co.uk> wrote:

--

Chris Albertson
Redondo Beach, California

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and follow the instructions there.

On 4/17/13 12:18 PM, Chris Albertson wrote:

since you can buy cake pans in even inch increments, I think the cake
pan will work..

BTW, I've been looking at some choke rings with only 2 rings instead of
the usual 3.  Apparently, the performance isn't all that much different.
When I asked why do all the other ones have 3, it boils down to "the
first one had 3 and everyone just copied it".

Javad has a bunch of choke ring theory..
http://www.javad.com/jns/index.html?/jns/technology/Single-Depth%20Low-Multipath%20Choke%20Ring.html
http://www.javad.com/jns/index.html?/jns/technology/Choke%20Ring%20Theory.html

Their conclusion is you want the depth of the ring to be slightly more
than 1/4 lambda.  lambda/4 for L1 is 1.87" so a 2" cake pan is just
about the right size.

If I read the paper correctly you can skip the choke ring if you mount the
antenna on top of a 2 meter or longer mast.  Iron pipe comes on 10 foot
lengths.  The choke ring is for portable survey antenna that can't be
placed on tall rooftop masts.  I think a 2 meter pole on a roof pretty
much meets their criteria of multi path difference being over 10 meters.

I can see now why surveyers need the choke ring type antenna, because they
can not choose the location.  They need to place it where they need to
measure.  But timing is different, we can choose the best location which
would be two meters above the tallest object in the area.

The cake pan certainly would work.  This is not super critical.  They are
only blocking low elevation signals. and it would give you more option for
the location

On Wed, Apr 17, 2013 at 8:14 PM, Jim Lux jimlux@earthlink.net wrote:

--

Chris Albertson
Redondo Beach, California

On 4/18/13 12:01 AM, Chris Albertson wrote:

yes.. multipath that is more than a chip away is generally filtered out
by the PN tracking loop, so all you really worry about is  multipath
signals within a chip.  For C/A code at 1 Mchip/sec, the chips are 300
meters long. If you're doing P/Y code, it's a tenth of that.

In reality, if the multipath signal is lower, and it's "far" away (a
good fraction of a chip) it doesn't contribute much to the output of the
correlator.  So their 10 meter thing is probably a good number for a
"typical" receiver they make.

On 04/18/2013 04:00 PM, Jim Lux wrote:

It's an interesting mix of sample-rate/bandwidth, code you track and
distance between early-late detectors (normal distance is one chip)
comes in when analyzing and combat the multi-path. I recall there is
some subtle points with some of the C/A codes.

Cheers,
Magnus

I hope I am not steering the thread to much, I have an Allen Osborne TurboRogue SMR12 RM L1 L2 GPS rec that came from JPL that appears specifically designed for Common View use. Does anyone know the history of these ,I can find almost nothing.
Email me directly if you have info, or I can start a new thread.
Tom Knox actast@hotmail.com