---------- Forwarded message ----------
From: Chuck Dietz <w5prchuck@gmail.com>
Date: Sun, Feb 8, 2015 at 11:15 AM
Subject: Re: [TowerTalk] Coax lengths for phasing a stack
To: Markku Oksanen <ww1c@outlook.com>
I am not sure of the question, but I have thought about putting the
switchbox at the center of a 3 Yagi stack and feeding the center Yagi with
X length coax and the upper and lower ones with X+1 wavelength coax. This
might reduce the total amount of coax.
Chuck W5PR
On Sun, Feb 8, 2015 at 10:11 AM, Markku Oksanen <ww1c@outlook.com> wrote:
> I have a four stack of tribanders on two different towers and one of them
> is with equal length lines to the bottom and the second one is with lines
> that have a bit of calculations behind them. Those terminate at to a 4:1
> broadband transformer at the middle of the tower. The length is such that
> it is an odd number of electrical wavelengths on 15 m. This is because a
> quarter wave line forces the current at the antenna feed point to be the
> voltage at the other end divided by the line impedance. This also makes
> sure that the phase is the same. I did this because the 15 m band SWR
> profile was the worst, on 20 and 10 the lines are about 1/2 wave or X times
> 1/2 wave. So, for any HF stack where the antennas are in different
> environments or slightly different on their own, this approach better
> guarantees proper phasing. I have an Excel sheet to calculate these that I
> can share if needed.MarkkuOH2RA/OG2A/WW1C
> > From: john@kk9a.com
> > To: towertalk@contesting.com
> > Date: Sun, 8 Feb 2015 10:28:11 -0500
> > Subject: Re: [TowerTalk] Coax lengths for phasing a stack
> >
> > While this does one really answer your question of using different
> feedline
> > lengths, I use equal lengths of coax with no particular length in
> regards to
> > wavelength. Mine all run to the base of the tower. You could save a lot
> of
> > coax by having them meet in the middle however if you use switching then
> > your relays are 150' in the air in your example. If you used four yagis,
> > you could group them on the tower and bring only a pair of feedlines down
> > the tower for switching and save some coax. FWIW, LDF4 is much easier to
> > coil up on the tower than LDF5 and it is inexpensive if you shop around.
> >
> > John KK9A
> >
> > To: TowerTalk@contesting.com
> > Subject: [TowerTalk] Coax lengths for phasing a stack
> > From: Grant Saviers <grants2@pacbell.net>
> > Date: Sat, 07 Feb 2015 18:48:10 -0800
> >
> > 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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