Joe,
>> > A possible mechanism occurs to me. High-precision GPS is
>> very vulnerable
>> > to multipath errors. A loos connector will have a
>> significant reflection.
>> > The reflected energy will propagate backwards, and be reflected off
>> the
>> > transmitter output discontinuity, the twice-reflected energy
>> propagating
>> > back to the receiver. The original and the triple-transit
>> echo will add
>> > coherently (for the modulation, not the photons) in the
>> receiver. This
>> > is
>> > a perfect multipath scenario. How long must the cable be?
>> Depends on the
>> > relative strength of main signal and triple-transit echo.
>>
>> > Joe Gwinn
>>
>> Joe,
>>
>> High precision GPS receivers use various correlator schemes that try to
>> minimize multipath. "Normal" GPS receivers are more vulnerable than
>> geodetic quality receivers.
>>
>> http://webone.novatel.ca/assets/Documents/Papers/PAC.pdf
>
> You are of course correct, but timing receivers may not go to such lengths
> are are needed for geodetic receivers. A lot of the magic of geodetic
> receivers is in the choke-ring antenna, which ignores signals arriving
> from
> too low an angle above the horizon.
>
> In the Neutrino case, the multipath is built into the cable between
> antenna
> and receiver, so the antenna cannot help. But I will read the article,
> which looks interesting. Wonder if it would solve such a triple-transit
> echo problem.
>
> Joe
I am not discussing antenna multipath attenuation. That is a separate
topic. Look at figure 12 in the Novatel paper - noting for the y-axis -
that 1 C/A chip length is about 300 meters.
Here is an article from the Ashtech/JPS/JNS/Topcon-family.
http://tinyurl.com/7w9wl4p
Overview results are seen in figure 5.
Timing receivers used by time-labs to compare Cs are usually geodetic
receivers with the option to lock the internal clock to external
10MHz/1PPS signals coming from the Cs.
My point is that good receivers attenuate multipath fairly well.
Is it known which GPS receiver type was used in the Neutrino experiment?
--
Björn
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