Mal,
You are certainly correct in being able to have the phasing box at the
antenna (or anywhere else you might be inclined to run the two coax ant feed
cables to).
My bet is it is a function of cost. I run LMR 600 to my phase box and it is
about 300 ft, I can't say for sure, but my bet is the cost of 300 ft of 3
conductor"bell wire" is a tad less expensive than 300 ft of LM 600 and two
connectors (the Poly Phaser lightning arrestors are a "wash") assuming the
phasing and control box are in the shack and not outside.
Also I beleive you want to have the phasing lines to be 1/4 wave (or 1/2
wave multiples of that) including velocity factor. I am not an engineer,
but what I have picked up is that allows you to "force feed" the antennas
with equal current (or something to that affect).
Dick K8ZTT
----- Original Message -----
From: "N7mal" <n7mal@citlink.net>
To: "Dick Williams" <k8ztt@mho.com>; <towertalk@contesting.com>
Sent: Monday, March 09, 2009 10:55 PM
Subject: Re: [TowerTalk] phasing multiband verticals
>I am going to step in & out of this thread many times only because of my
> experiences/work at/on phased vertical arrays.
> Who and more importantly WHY was the decision made that the phasing must
> be
> done at the antennas.?.?.?. You can do the phasing in the shack and not
> have
> to run a voltage to the antennas and also isolate the stray R.F. path back
> into the shack.
> Why not run 2 equal lengths of coax from the antennas back into the shack,
> preferably not in a length of 1/4 wave multiples. (Wavelengths are
> calculated with velocity factor in all phased arrays)
> Just my -2cents worth
>
>
> MAL
> N7MAL
> BULLHEAD CITY, AZ
> http://www.n7mal.com
> Everyone in the world is
> entitled to be burdened
> by my opinion
>
> ----- Original Message -----
> From: Dick Williams
> To: towertalk@contesting.com
> Sent: Tuesday, March 10, 2009 2:32
> Subject: Re: [TowerTalk] phasing multiband verticals
>
>
> Jamie,
>
> I have two Force 12 160 mtr verticals that I have spaced at 1/2 wave and
> am
> using the ComTek PVS-2 system. It uses a three wire configuration to
> switch
> three directions. Before I bought that, I was using a home brew phasing
> system that gave me either an end fire or cross fire pattern (feeding in
> phase or 180 out). The nice thing about the ComTek is it uses a 2.25:1
> UNUN
> for the in phase matching and an electric 90 degree phase shift to give
> gain
> for either direction of the end fire.
>
> Actually the best spacing for their system on 40M is 49 ft (more than a
> quarter but less than a half). I use 1/2 because that gives me better
> cross fire gain at the expense of some end fire gain; and my verticals are
> on a NW/SE line (NE/SW would be better, but that wouldn't work at my QTH).
>
> I have mono band antennas for all the bands and only run one coax and two
> rotor cables into the shack. I designed and built a remote switching
> system
> that uses +, -, 0, and AC down the coax along with a hard wire to the
> first
> relay box that I use the same voltages to swith the one coax out to the
> first four runs to additional switch boxes. The only reason I have two
> rotor lines is I needed a seperate one for the Orion 2800. All the other
> rotors are Hy-Gain and I remote switch them so I only have one CDE (Hy
> Gain)
> rotor box in the shack.
>
> You might look into control voltage down the coax; and if you run a
> single
> wire out to a coax switch box (like the Ameritron RCS-4) you can switch 16
> antennas with four additional boxes. I have three of the RCS-4s along
> with
> a couple of MFJ-4712's to do all my switching. I called them up and
> bought
> just the relay boxes, and then modified them as necessary to work as I
> needed them to.
>
> I will say that I have been very pleased with the ComTek PVS-2 on 160M.
>
> Good luck
>
> Dick K8ZTT
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
>
> --------------------------------------------------------------------------------
>
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 8.0.237 / Virus Database: 270.11.9/1991 - Release Date: 03/09/09
> 07:14:00
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|