[TowerTalk] Coax lengths for phasing a stack

[David Robbins]

The only true way to do it is to keep all the lines the same length.  Yes,
this may end up with extra line coiled up here and there, but it keeps all
the phasing lines equal.  

One thing to keep in mind is that a wavelength of coax is only a wavelength
at a single frequency.  Cut a wavelength at 3.5Mhz and its 1.14 wavelengths
at 4Mhz.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net


-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Grant
Saviers
Sent: Sunday, February 08, 2015 02:48
To: TowerTalk at contesting.com
Subject: [TowerTalk] Coax lengths for phasing a stack

I'm ruminating about what lengths I need for 5L over 5L stacks to equalize
the antenna feedpoint phase.  The literature seems thin and the common
answer is "make the feed-lines the same length", which I am certain will
work.

However, when the stack separations are sufficient, there may be more than 1
wavelength of coax needed to equalize the lengths.  e.g. 60' 
separation on 20m at 0.89 vf (LDF5) is just about 1 wl.  It seems to me
there is little downside with ham radio modulation systems to phase at 0
(equal lengths) or +/- n * 360 degrees (where n is 1 or 2).  Perhaps some cw
waveshaped attack/decay envelopes will change a tiny bit, but that seems
like a slight downside.

So it may work out that no extra phasing line is needed for certain
separations.  I am planning that all misc lengths of coax's and types are
the same for both antennas (rotator loops, boom and choke lengths).

Then there is the slightly counter-intuitive result that making the longer
(higher antenna) feedline a bit longer minimizes the coax used in the
phasing at some separations.  And one more trick would be to reverse the
outputs of one side of the TLT matching transformer for BIP to eliminate 1/2
wl of phasing line.  It wouldn't matter for Top or Bottom only use.

So, is this analysis correct?  Any other options for using less coax?

Grant KZ1W
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