[TowerTalk] FW: Determining coax length?

KM5VI km5vi at flukey.cc
Tue Nov 12 17:20:44 EST 2013

John makes an important point about taking time to confirm the polarity of
the baluns - I have seen two baluns from the same manufacturer with
identical part numbers that were wired with the load side connections
internally reversed with respect to the casing of the unit.


-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
john at kk9a.com
Sent: Tuesday, November 12, 2013 10:06 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Determining coax length?

I also cut the cables the same length before installing the antennas by
laying them flat on the ground. I build identical antennas and use the same
model balun. When connecting the baluns it is very important to connect them
identically (center of the coax to the same side of the driven element for
each beam).

John KK9A

To:	towertalk at contesting.com
Subject:	 Re: [TowerTalk] Determining coax length?
From:	 David Robbins <k1ttt at verizon.net>
Reply-to:	k1ttt at arrl.net
Date:	 Tue, 12 Nov 2013 07:58:10 -0600 (CST)

well, you can probably get close enough by using the mechanical drawings for
the antennas to get the length of coax along the boom to the boom-mast clamp
then measure it from there.

any of the electronic measures will be less precise, but if you are careful
and measure them all the same way you can probably get close enough if you
just calculate the differences in length and not the absolute length.

Personally I prefer to cut all the feedlines the same length when populating
a tower, this means that some of them are too long and end up coiled on the
tower but it gives the best matching of the phases.

Nov 12, 2013 08:50:28 AM, rich at n7tr.com wrote:

I am stacking several mono banders with a stackmatch II. I have the antennas
mounted on the towers, but the coax feedlines are different lengths right
The Stackmatch wants coax lengths to both antennas to be the same length,
but I'm unable to physically measure to the end of the feedpoints on the
coax is the same (RF Davis Buryflex)


1) How critical are the coax lengths to the stackmatch from each stacked
2) What tools can I use to determine the length of coax to each antenna?
(AIM 4170, MFJ, etc?) and how do you determine equal lengths?


Rich N7TR
Telnet: dxc.n7tr.com N7TR DXCluster


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