[time-nuts] GPS antenna length correction
wbeam at gci.net
Tue Apr 29 01:15:02 EDT 2014
On Mon, 28 Apr 2014 21:24:56 -0700, Tom Van Baak wrote:
>> Accounting for the cable delay will only correct the absolute time.
>> Imagine a 100m antenna feed line; the receiver could be anywhere within
>> 100m of the antenna (even above it or at it). The algorithm that computes position
>> needs to know this.
Please read all of what I stated.
>What the algorithm computes is position -and- time at the antenna.
>It doesn't care where the receiver is, or how long the cable is.
>The GPS solution gives the place and time of the antenna only.
>1) If you want to translate the antenna solution to some other physical place, then apply a dX,dY,dZ correction.
>2) If you want to translate the antenna solution to some other physical time, then apply a dT correction.
>1) If the antenna is on top of a pole but you actually want the true location of the base of the pole, you apply a spatial correction.
>2) If the antenna is on top of your roof but you want the true time at a BNC jack in your lab, you apply a temporal correction.
>The GPS timing receivers most of us use make it easy to apply a temporal correction, but not a spatial correction.
>Consequently, your lab receiver can be configured to pulse the true time at center of the front panel BNC.
>But, your lab receiver cannot be configured to show the true location of the center of the front panel LCD.
>Instead, the LCD is stuck showing the location of your distant antenna.
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