The easiest way to do your job is with a Time Domain Reflectometer (TDR). I've
had no trouble making precision cable length measurements
with my HF antennas connected.
I also use the TDR to check transmission lines and phasing accuracy from inside
the shack, there's no need to haul the TDR outdoors.
During my annual preventative maintenance, I use my TDR in shack to
check all of my feedlines and phasing lines and compare the results
with prior years. With a WX0B stackmatch, you can check each phasing
line individually. Of course, I also keep records of the VSWR sweeps
Its a whole lot easier to check the condition of 8 Beverages with a TDR
than to go out and walk them in the snow! The TDR will check the
feedlines and the Beverage antenna as well. If a Beverage wire falls
down, its immediately obvious from the TDR in the shack.
Very affordable TDRs are listed for sale on the eBay and other sites.
You don't need an new one, although a nice compact portable TDR would
be lots handier than my 40 year old Hewlett Packard TDR!
---- Original message ----
>Date: Thu, 15 Mar 2007 11:22:06 -0400
>From: Mike <email@example.com>
>Subject: [TowerTalk] Phase Relation of Different Cables
>Questions: what is a method for determining the phase relation of a
>pair of cables? How to adjust the cables to have the same
>phase? The cables are made of two different kinds of coax, FSJ-4
>and RG 213. The cables are different length. One of the cable
>combinations is more than a wave length at 7 MHz. The reason for the
>question is the desire to move all the antenna switching mechanisms
>off of the tower to the base.
>The ant. system is a pair of F12 EF240Xs, one at 145 feet and the
>other at 70 feet; pair of 4 element SteppIRs, one at 132 feet and the
>other at 100 feet; 80 meter inv. vee with apex at 120 ft at the end
>of a three foot standoff from the tower. The EF240Xs and SteppIRs
>are controlled by homemade stack matching devices (using 2 to 1
>ununs). Band selection of the antennas, EF240Xs, SteppIRs and 80 m
>inv. v, is made using homemade ant. selectors. Also, the ant.
>system can be split for SO2R using a homemade A:B switch. All the
>switches and stack matching devices are mounted on the tower from ~
>80 foot to 110 foot level. Desire is to remove all the switches and
>stack matching devices from the tower and put in a single box at the
>base of the tower reducing the need climb the tower to repair/replace
>(although hasn't been required in the two years they have been in
>place) any of these devices. Figure coax is more reliable than relays, etc.
>Presently there are two runs of FSJ-4 on the tower, radio 1 and radio
>2, and would like to keep them but they are different length. Want
>to use LMR-400 for the additional runs to the ant. from the base of
>the tower. RG213 will be used for rotation loops where required.
>Thus the reason for the above question.
> Mike, K4GMH
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