[time-nuts] GPS active antenna delay ?

[Tom McDermott]

Hi all.

The papers are:

1) "SAW Filter Modeling in MATLAB for GNSS Receivers", S.H. Abbas, et al.,
IJECE Oct 2013, ISSN: 2088-2078
The authors de-embed the group delay using FFT and MATLAB. Eyeball about
15-20 nsec. for a pretty wide filter.

2) "The Effects of SAW Group Delay Ripple on GPS and Glonass Signals",
Simon Adams, Novatel, Inc., Calgary AB
The author computes a group delay ripple of 38 nsec for a specific SAW
filter due to triple-transit reflections.

3) "GPS + Modernized GPS + Gallileo Signal Timing Biases", Chris Hegerty,
Ed Powers, Blair Fonville, all of USNO, GPS World, March 2006 pp 49-54.
Figure 2 shows group delay minima of about 65 nsec. for the RF/IF filtering.

4) Arbiter Systems Datasheet for AS0087800 active timing antenna, the
datasheet is numbered PD0050600A. Arbiter systems, Paso Robles, CA. They
specify (or measured?) the antenna delay exclusive of any cable as 43 nsec.

In reading through the various SAW filter specifications on the web, I've
found a few that specify the group delay ripple, but none that specify the
group delay itself.


-- Tom, N5EG












On Sun, Feb 8, 2015 at 2:11 AM, Attila Kinali <attila at kinali.ch> wrote:

> On Sat, 7 Feb 2015 10:07:44 -0800
> Tom McDermott <tom.n5eg at gmail.com> wrote:
>
> > While compensating for cable delay is relatively straight forward by
> > measuring the length and compensating for
> > the velocity factor, a question is: how much amplifier / filter group
> delay
> > is to be expected within the antenna itself?
>
> The usual way is to calibrate the whole setup, including antenna, LNA,
> cable and receiver. Ie. you drive to the national lab, set up your whole
> system, then measure the timing difference of your GPS receiver to the
> one of the lab, drive back home, and apply the correction.
>
> > Looking through GPS SAW filter datasheets seems to show none with group
> > delay specifications.
>
> Not surprising. Group delay is not considered of any importance in most
> RF designs.
>
> > googling leads to some research papers with delays of about:
> >
> > L1 - 20 MHz wide SAW filter has about 15 nsec of group delay
> > L1 - 2 MHz wide SAW filter has about 65 nsec of group delay
> > L1 - LC filter - can't find anything, but suspect it's probably just a
> few
> > nanoseconds.
>
> I would be very much interested in those papers. Could you list their
> titles
> and authors at least?
>
>
> > I'm not sure a consumer grade antenna even has a SAW filter, it may
> simply
> > be an LC filter.
>
> Unlikely. LC filters are not sharp enough and difficult to build reliably
> at those frequencies. I would rather assume that there are no filters
> at all (beside the antenna characteristics).
>
>
>                         Attila Kinali
>
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
>                  -- Miss Matheson, The Diamond Age, Neil Stephenson
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