[TowerTalk] Tuning raised radial verticals

Sat Sep 2 11:13:23 EDT 2017

When I first put up my array, I only cared about the CW window, and again, used bottom fed coils with and alligator clip to go from the PH band to the CW band after  some revisions.  I agree with Bob that the more power dumped in the dummy load off the comtek port reduces F/B but we all have our particular tolerances for that.....most likely I did notice worse performance at less than 30%, so thanks for the correction.  I had it from 1999-2003 and it took up 2 acres with the radial field.  The Low Band Monitor had a contest every year back then for stations who worked the most zones and 3 out of 4 years I worked all 40CQ zones.  I had home brewed top loaded aluminum verticals.... I dont know why anyone would build a four square without the comtek, right?!  Like I said, yoy can see it on my qrz.com<http://qrz.com> page and several articles on Tower Talk archives from 1999-2001.

73. Paul.  N0AH

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On September 2, 2017 7:25:10 AM "Bob Shohet, KQ2M" <kq2m at kq2m.com> wrote:

No, that is not correct and both of my 4-squares use the Comtek Hybrid.  Of course I care about 3% – at 3.5 mhz, that 3% changes the resonant freq. of the array (and minimum dumped power to the dissipating resistor) by more than 100 khz!  A resonance of 3.5 mhz vs. 3.6 mhz would significantly reduce the ability of the 80 meter 4-square to effectively cover BOTH the cw and lower ssb band – and with dumped power rapidly increasing above the recommended 5% level, could damage the hybrid as well.  Not to mention reduce the forward power to and affect the performance of the array at the frequencies that matter most.  Why would I want to allow any of that to occur?

I have noticed little change with wet elements although I used pvc coated wire so perhaps that might reduce the effect that you describe vs. bare wire.  The only time I see a large change in resonance is when my 4-squares are encased in ice due to the frequent ice-storms we get at my qth –( averaging 6+ per year over the past 22 years!)

Bob KQ2M

From: Bryon Paul Veal NØAH<mailto:bryonveal at msn.com>
Sent: Friday, September 01, 2017 1:22 AM
To: Bob Shohet, KQ2M<mailto:kq2m at kq2m.com> ; john at kk9a.com<mailto:john at kk9a.com> ; towertalk at contesting.com<mailto:towertalk at contesting.com>
Subject: Re: [TowerTalk] Tuning raised radial verticals

but with a comtek hybred coupler, you will never care aboit that 3%....plus
the skin effect of wet radiators cause much bigger resonant changes that
again,  the hybred couplers dummy load soaks up.... what are you people
using to phase your arrays?

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On August 31, 2017 8:09:04 PM "Bob Shohet, KQ2M" <kq2m at kq2m.com> wrote:

> My understanding is the mutual coupling between the four 1/4 wavelength
> verticals tends to raise the resonant frequency by ~ 5%, (that is what I
> have read in numerous places), meaning that you want to start with by
> cutting the 1/4 verticals for approximately 5% lower in freq. (longer) than
> where you actually want it to resonate.   My actual experiences with
> building multiple 4-squares on 40 and 80 is that the resonant freq. tends
> to be raised by ~ 3 %, not 5%.  Furthermore, if you use pvc coated wire
> like I do, that has the effect or lowering the resonant freq. by an
> additional ~ 2%.
>
> So when I build or rebuild a 4-square, I cut the 1/4 wave elements for
> about 5% below the “target” resonant freq. and then the array typically has
> minimum reflected power (resonance) within ~ 1% of where I actually want it
> to resonate.  I use 3 – 4 elevated radials per element.  I do not know
> whether or not these resonant freq. shifts are the same or different with
> elements near the ground and 30 – 60 ground mounted radials, or whether or
> not there is a difference in resonant freq. shift with using a 4-square on
> open ground without trees.  (I am in very dense forest).
>
> I suspect that terrain, forest vs. open field, and ground-mounted vs.
> elevated radials, affect the amount of coupling between elements and the
> freq. “shift” that one must take into account when cutting their elements.
> It also goes without saying that most elevated 4-squares do NOT use a
> “spider-web” of twine (box + “x”) to keep the adjacent and opposite element
> spacing exact – differences in element spacing will likely affect the
> resonant freq. shift as well as any differences in the lengths of the 75
> ohm feedlines between the elements and phasing box.
>
> I suspect that often when a 4-square is “off” from where it is expected to
> resonant, it is because either the element lengths, spacing and feedline
> lengths are not exact – or there is something NON-equivalent in the coax
> (Velocity factors can and often differ in the same cable at different
> points within the same roll of coax! – which is why each feedline must be
> measured first for physical length and then tuned for electrical length).
>
> 73
>
> Bob KQ2M
>
> From: john at kk9a.com
> Sent: Thursday, August 31, 2017 9:36 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Tuning raised radial verticals
>
> What is the reason for making the verticals 4% long?  I am far from being a
> 4sq guru however it would seem that you should have a choke, especially with
> an elevated feedpoint. It is easy to make one using a short piece of RG-302
> and a few ferrites that will leave your phased feedline long enough to still
> reach the control box.
>
>
> John KK9A
>
>
> To: Bryon Paul Veal NØAH <bryonveal at msn.com>, Towertalk Reflector
> <towertalk at contesting.com>
> Subject: Re: [TowerTalk] Tuning raised radial verticals
> From: Rudy Bakalov via TowerTalk <towertalk at contesting.com>
> Reply-to: Rudy Bakalov <r_bakalov at yahoo.com>
> Date: Thu, 31 Aug 2017 21:23:25 +0000 (UTC)
> List-post: <mailto:towertalk at contesting.com>
> I am measuring the impedance at the very base of the vertical with a
> calibrated
> RigExpert. According to DX Engineering the vertical should be connected
> without
> any baluns, matching networks...nothing. Furthermore, they are saying that
> the
> vertical should be resonant 4% of the target array frequency. That is, in my
>
> case, if I want to tune the array for 3.550 each individual vertical should
> be
> tuned for 3.413.
> Rudy N2WQFrom: Bryon Paul Veal NØAH <bryonveal at msn.com>To: Rudy Bakalov
> <r_bakalov at yahoo.com>; Towertalk Reflector <towertalk at contesting.com>Sent:
> Thursday, August 31, 2017, 4:34:40 PM EDTSubject: Re: [TowerTalk] Tuning
> raised
> radial verticals
> your seeing changes in the FEEDPOINT impedance using a tuned raised radial,
> thus your SWR will move  if yoy mess with them.  Suggest you consider using
> UnUns at the feedpoints to match the coax impedence to that of the
> verticals.  Also, a Comtek hybred coupler.....
>
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