[TowerTalk] phasing antennas

[Frank Donovan]

Hi Gregg,

Can you borrow a time domain reflectometer?   They are widely
available these days because of their relatively low cost and
widespread use in the wireless and CATV industries, among others.

There's no legitimate reason to cut your cables to anything other than
equal length, there's no benefit to multiple-1/4 wavelength lines for
Yagis with matching networks (T-match, Gamma-match, Beta-
match) at their feedpoints.  All of my Yagi array switching is located
at the tower bases, except for my 40 meter stacks which use two
long feedlines to array switching located in the ham shack.

I simply use a tape measure to cut the phasing lines to approximately
equal length and I leave the cable end bottom of the tower
unterminated.  After installation of the antennas and feedlines is
complete, I cut the cables to the length needed to connect them
to the StackMatch, then use a TDR to cut each of  them to
precisely the same length.   This is very accurate on 40, 20, 15
and 10 meters, and should be equally accurate on 6 meters.

An added benefit to this technique is that the TDR allows you to clearly
see the distinctive "signature" of the T-match on each Yagi, and you
can verify that all Yagis in the stack look identical to the TDR,
and hence to the stackmatch.

The TDR is a great tool for detecting defects that may creep into
antennas, matching networks, feedlines and connectors over time.
Keeping good records is essential to the success of this method.

An advantage of using T-matches is that you can measure
the DC resistance of the entire feedline, connector and T-match
system.  Any significant change in the DC resistance of the
system is an indicator of a maintainance problem.

73!
Frank
W3LPL
donovanf at erols.com




----- Original Message -----
From: Gregg Seidl <k9kl at direcway.com>
To: <>
Sent: Monday, March 14, 2005 8:43 PM
Subject: [TowerTalk] phasing antennas


> Thanks for all the help!!Just to clarify a few things.The antennas will be
> spaced 27 feet,as per M2's specs.The top one will be at 70 feet and the
> bottom one will be at 43 feet.I will be using Phillystran(where can I get
> some,Texas Towers?)for guying since the guys will be "in the way".The
cable
> is LMR-600.The "stack-match"is really a Comtek box and yes it is designed
> for 6 meters.I got this "crazy"idea from an article in NCJ last spring.The
> antennas are M2 6M-9KHW's.They are fairly large.When I said the same
length
> with my 269 I didn't mean they needed to be a 1/4 wave or multiple ,I just
> meant they needed to dip at the same freq,wwherever they were an odd 1/4
> wavelength to make sure they REALLY were the same length.I have made
phasing
> lines for 1296,that is tricky.Again thanks for the help.I am I missing
> something?  Gregg
>
>
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>
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