[TenTec] GPS Antenna feedline

[WA2BPE]

While generally correct as to Vp values, some manfacturers dielectric has some
"quality control" issues (hence Zo isues too) and the classic numbers don't
apply.  You can usually expect Vp to be good for Andrew, Times, Belden, etc, but
watch out for RS and a few others (and even the big names have problems at
times).  Many folks have wondered why coax baluns by the formula don't work
right only to find out the calculated length isn't correct.  The one sure way is
to "dip" the coax and calculate the Vp based on the frequency and physical
length.

>From a practical sense, it may not be necessary to enter this number at all -
depends on your use - if it is just a super-stable 10MHz reference, a phase
delay is probably of little concern.  Time, OTOH, may or may not be a worry;
again, it is the application.

73,

Tom - WA2BPE

Carl Moreschi wrote:

> You need to tell the GPS receiver the antenna feedline delay in nanosecs.
> For free space, light travels at 11.8 inches in 1 nansecond.  If the coax
> has the hard tpye insualtion material in it, its propagation factor is 66%.
> If the coax has foam insolation, its propagation delay factor is 82%.  So if
> you take the length of the coax in feet and divide it by either 0.66 or 0.82
> , you will get the total delay in nanoseconds.
>
> So 50 feet of coax with hard insolation will be 75 nanoseconds delay.  Now
> all you have to do is tell the GPS receiver what your antenna delay is.  In
> the "Control and Query" window, select "Antenna delay" to send the command.
>
> Carl Moreschi N4PY
> Franklinton, NC
> ----- Original Message -----
> From: "Mark Erbaugh" <mark at microenh.com>
> To: <tentec at contesting.com>
> Sent: Thursday, June 26, 2003 12:48 AM
> Subject: Re: [TenTec] GPS Antenna feedline
>
> > Well, I got things working!  I took a piece of RG8X because I had it some
> > and attached BNC connectors to both ends after running it through the
> house
> > band board into the shack.  I used an old PC network BNC T ( again because
> I
> > had one ) connector as a splice between the BNC on the antenna and the
> > extension.
> >
> > The signal strengths ( I assume that that is the SS column on the SatStat
> > display - with the clock outside, directly connected to the antenna I saw
> > numbers peaking around 160, this evening the highest is about 70 ) are
> down,
> > but the clock was able to track 6 satellites in about 15 minutes.  Now to
> > let the clock stabilze.
> >
> > This is probably in the manual, but do I need to adjust for the additional
> > length of coax that I added? Is there a way to let the clock figure that
> > out?
> >
> > 73,
> > Mark
> >
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