[time-nuts] antenna length
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Thu May 17 18:09:26 EDT 2007
> John WA4WDL
> ----- Original Message -----
> From: "Howard W. Ashcraft" <hashcraft at hansonbridgett.com>
> To: <time-nuts at febo.com>
> Sent: Thursday, May 17, 2007 5:44 PM
> Subject: [time-nuts] antenna length
>> Simple question.
>> I have a stock trimble thunderbolt that I am currently running with a
>> generic active gps antenna. I know that you "should" offset for the time
>> delay of your antenna feed line. However, it would think that the timing
>> offset is important for determining the actual time, but not necessary if
>> you are only wanting a stable 10 mhz output. Is there a consideration
>> that I am overlooking?
>> HOWARD W. ASHCRAFT, Jr.
>> Direct Dial: (415) 995-5073
>> hashcraft at hansonbridgett.com
>> HANSON 425 Market Street, 26th Floor
>> BRIDGETT San Francisco, CA 94105-2173
>> MARCUS Direct: (415) 995-5073
>> VLAHOS Main: (415) 777-3200
>> RUDY, LLP Fax: (415) 995-3460
Not quite correct.
If the antenna cable is long enough the diurnal variations in its delay
will be noticeable.
However with a Thunderbolt the cable will need to be kilometers in
length for this to become significant.
The diurnal variation in the delay of the various amplifiers required
with such cable lengths is even more significant.
With short cable lengths the diurnal variation of the antenna and/or
receiver delay is more significant.
With a more accurate timing receiver and/or wider diurnal temperature
swings the effect may be noticeable with shorter cable lengths.
With GPS carrier phase measurements the diurnal delay variation of a
cable as short as 20m should make a good thermometer.
However the antenna and/or receiver delay will be more significant.
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