[time-nuts] GPS active antenna delay ?

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Thu Feb 19 12:22:36 EST 2015


On 18 Feb 2015 04:20, "Tom McDermott" <tom.n5eg at gmail.com> wrote:
>
> 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.

I don't see why. The two antennas can (and should) be a reasonable distance
apart. There will be no significant interaction between them.

The biggest problem might be reflections from the ground.

> 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.

If it was a 10-15 minute job I would not mind doing it for you as I have
several VNAs that cover 1.5 GHz.

But it would take quite a bit of time to build the appropriate antenna then
mount the two in such a way that reflections were not an issue.  It means
errecting two masts on non conductive poles. It is basically a days work.

If you have a spectrum analyzer, you could probably see the bandwidth of
the filters from looking at the noise spectrum.  From what someone wrote
earlier,  with typical delays vs bandwidth,  you could perhaps get a rough
estimate of the delay.

I just wonder if there's some other way, especially if one has multiple GPS
receivers,  a fast scope.... but I can't think of anything.

A VNA is the obvious tool to me, but I would not be surprised if there was
some trick that could be used without a VNA.

> Thanks for the pointer to the Keysight VNA discussion list.

No problem.  For answers to VNA related questions,  the Keysight forums are
the place to go. Neither Anrisu or R&S have anything like this.

> -- Tom, N5EG

Dave.


More information about the time-nuts mailing list