[time-nuts] antenna length

[Dr Bruce Griffiths]

jmfranke wrote:
> Nope.
>
> 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.

Bruce