[time-nuts] GPS active antenna delay ?

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Mon Feb 16 21:12:16 EST 2015


On 7 Feb 2015 19:18, "Tom McDermott" <tom.n5eg at gmail.com> wrote:

> Has anyone on the list measured or otherwise estimated the active antenna
> delay including the amp and filters?
>
> -- Tom, N5EG

I have never done this, but suspect that using a VNA is the best way to
go.  With a simple passive dipole on one port, and the active antenna and
cable on the second port, a transmission measurement (S21) is probably the
way to go. But I was unsure of exactly how to do it.

Your question prompted me to ask on the Keysight VNA forum. There's a reply
by Dr. Joel Dunsmore - one of the worlds leading authorities on VNAs.

http://www.keysight.com/owc_discussions/thread.jspa?threadID=39151&tstart=0

He asks what accuracy is needed. Being time-nuts, I think the answer is "as
high as possible". He writes

"With this method, 1 nsec is reasonable, but if you need 100 psec or 10
psec, then we will have to be much more careful."

You might want to contribute to that forum post.

Dave.


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