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
Sent: Friday, September 01, 2017 1:22 AM
To: Bob Shohet, KQ2M ; john@kk9a.com ; towertalk@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@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@kk9a.com
> Sent: Thursday, August 31, 2017 9:36 PM
> To: towertalk@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@msn.com>, Towertalk Reflector
> <towertalk@contesting.com>
> Subject: Re: [TowerTalk] Tuning raised radial verticals
> From: Rudy Bakalov via TowerTalk <towertalk@contesting.com>
> Reply-to: Rudy Bakalov <r_bakalov@yahoo.com>
> Date: Thu, 31 Aug 2017 21:23:25 +0000 (UTC)
> List-post: <mailto:towertalk@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@msn.com>To: Rudy Bakalov
> <r_bakalov@yahoo.com>; Towertalk Reflector <towertalk@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.....
>
> Sent with AquaMail for Android
> http://www.aqua-mail.com
>
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