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
Sent with AquaMail for Android
http://www.aqua-mail.com
On September 2, 2017 7:25:10 AM "Bob Shohet, KQ2M" <kq2m@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@msn.com>
Sent: Friday, September 01, 2017 1:22 AM
To: Bob Shohet, KQ2M<mailto:kq2m@kq2m.com> ;
john@kk9a.com<mailto:john@kk9a.com> ;
towertalk@contesting.com<mailto: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?
Sent with AquaMail for Android
http://www.aqua-mail.com
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
>
> _______________________________________________
>
>
>
> _______________________________________________
> 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
_______________________________________________
_______________________________________________
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
|