[TowerTalk] Antenna Distance From Shack

[Jim Lux]

At 10:23 AM 8/18/2006, you wrote:
>Hi Pete,
>
>Can you elaborate on the "1750 Hz (measured at 28 MHz) of 3/4" CATV" you 
>mentioned? First, I assume you meant 1750 KHz, but aside from that, I'm 
>not following what you mean.
>
>Also, measuring loss at the shack with the MFJ-259B... Unless you install 
>a non-resonant 50 ohm terminator at the opposite end, your readings in the 
>shack will continue to 'vary widely' (although maybe not as "widely"). If 
>you installed a 50 ohm load on one port of a remote antenna switch that 
>would accomplish the task, but I'm thinking this is not what you had in 
>mind regarding measuring loss.


If I were putting a relay at the far end, with the goal of measuring coax 
properties, I'd terminate it in a deliberate mismatch other than a short or 
open, and certainly not in a load matched to the line.  Maybe into 25 ohms 
(two 50 ohm loads in parallel).  Then, you could use your MFJ (or almost 
anything else) to get a pretty quick handle on what the actual cable 
properties are.

With a 50 ohm load at the far end, you won't be able to characterize the 
cable very well, because there won't be any reflected power for your meter 
to see coming back.

With an open or a short, you get a lot of power reflected, but then, you'll 
be making measurements at high SWR, where your meter is least accurate.




>73 de Bob - KØRC in MN
>
>
>Message: 2
>Date: Fri, 18 Aug 2006 08:13:14 -0400
>From: Pete Smith <n4zr at contesting.com>
>Subject: Re: [TowerTalk] Antenna Distance From Shack
>To: TOWERTALK at contesting.com
>Message-ID: <6.2.0.14.2.20060818080204.05175928 at mail.adelphia.net>
>Content-Type: text/plain; charset="us-ascii"
>
>Frank and Bill make good points.  For the last 10 years, I have been using 
>3/4" CATV for most of the 190-foot run from my house to my antennas.  To 
>be specific, I use RG-213 up the tower and across the roof of my house to 
>my 2nd-floor shack, but use multiples of a half-wave at 1750 Hz (measured 
>at 28 MHz) of 3/4" CATV in between.
>
>-- some stuff snipped here --
>
>I want to be able to monitor loss from the shack, something that my 
>composite feedline doesn't seem to let me do (the indicated loss on my 
>MFJ-259B varies widely with frequency).
>
>-- trailing text snipped  here --
>
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