[TowerTalk] Hardline Fault

[Jim W7RY]

Ok... My Bird Sitemaster SA-6000 handles it quite nicely. Do it all the 
time. I can see a ground kit on a piece of 7/8 Heliax and also the bend in 
the cable as well.

73
Jim W7RY


-----Original Message----- 
From: Jim Brown
Sent: Tuesday, August 21, 2012 9:02 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Hardline Fault

On 8/21/2012 4:59 PM, Jim W7RY wrote:
> All you have to do is run a distance to fault measurement with a precision
> load on the far end. Using a wide frequency range (100 to 1000 MHz or the
> maximum frequency range that will allow you to "see" 500 feet with your
> particular cable) you can see all of the imperfections along the cable.

That's generally good advice, BUT -- TDRs are implemented in several
different ways, and the limitations of one analyzer may be different
from those of another.

I use the DG8SAQ VNWA, which does a sweep and then an inverse transform
of the sweep to get the time response.  Using this method, any sweep
bandwidth and be transformed to view any length of line. Small
imperfections that don't show up at low frequencies will often show
clearly at high frequencies. That's why taking the sweep to higher
frequencies shows smaller faults. Also, with a linear sweep from 1 MHz
to 1 GHz, for example, half of the energy will be in the top octave
(that is, between 500 MHz and 1 GHz).  The transform method works quite
well even with an unterminated line, a line feeding an antenna, or a
matched load, and under all of those conditions can show a lot of small
perturbations on the line.

With the inverse transform method, the manner in which the data is
windowed can make a VERY large difference in the visibility of faults.
When I'm doing TDR, I often look at the data with several windows and
filter types.

73, Jim K9YC
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk