[time-nuts] GPS active antenna delay ?

[Tom McDermott]

Hi Dave - agree that VNA is one good way to measure the delay.  If required
accuracy is less than about
0.5 nsec, then Tx antenna to Rx antenna mutual impedance starts to become
an issue. Above about
1 nsec error probably most of these can be ignored.  No access to a vector
VNA that works at 1.5 GHz.
unfortunately.

Normally I would use a difference measurement (substitute known reference
Rx antenna for Rx
under test, and difference the two), but am afraid that the (reference
Rx-to-Tx) and the (Rx under test-to-Tx)
might have different mutual Z.

Thanks for the pointer to the Keysight VNA discussion list.

-- Tom, N5EG






On Mon, Feb 16, 2015 at 6:12 PM, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkirkby at kirkbymicrowave.co.uk> wrote:

> 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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