[TowerTalk] Quad Element Tuning
Mon, 10 Sep 2001 15:09:45 EDT
In a message dated 9/9/01 1:21:29 AM Pacific Daylight Time, email@example.com
I like plain and reliable systems, expecially with antennas.
If I where to install a single 5 bands antenna covering from 10 to 20
meters, I'd probably go for a log periodic or a trapped yagi.
Marri: I have no problem with your approach and I "often" use it also.
However a Log Periodic has reduced gain as does a trapped yagi, it's not used
by contesters and it's fixed. I like "improvements." I can make very quick
adjustments to any of my antennas very quickly--if ever needed. I will be
using a LP on VHF&UHF myself for it's "conveniences" and will have others not
so convenient in design for the serious stuff.
If I can retune the Reflector of a 2 element quad for max gain or F/B
quickly on 5 bands with a selsyn and calibrated 180 degree dial using far
less of that rotation distance which is an element of simplicity (actually 6
bands-I added 6M)--I have a technical and performance edge on the rest.
That's the name of the game for serious antenna students and that's very
cool! I seem to be the only one that has suggested this design. It's very
tough at times with new designs in particular on TT. The biggest design
obstacles are often the poo pooers who seldom try anything themselves--who
secretly use it later when it's developed.
In the interest of "Advancing the State of the RF Reshaping Art" (new term
I just coined), there are times when I will go the extra design and
mechanical complexity mile for a test period to see if there are areas that
can be improved. After a while I get bored with the status quo and need a
new challenge. Since I have the "Magic Wood Platform" for convenience on my
tower that a total of 5 now have asked to see pictures of and will be on the
front cover of 73 Mag, I can stand comfortably on it and have the assembly of
the 5 ganged variable Xc's right in front of me for maintenance and initial
adjustments in the matter of "1 minute." That's quicker than I can get at it
with a tip over or crank up tower. Some can't climb a tower and others would
rather not which I can't understand. I've been on my tower and wooden
platform as many as 20 times in one day when on a hot project--and I'm just
Come to think of it, some creative mfgs have a series of platforms for deer
hunters so they can sit up high out of the deer's normal vision in trees.
They even come with seat belts to keep them from falling out of it if they
fall asleep. You can even climb up a tree with them. No hunter with any
brains will climb a tree to hunt deer without one of these clever tree
stands. Hams haven't shown the same safety intellect working on big heavy
beams much higher on a tower with fewer things to stand or hold on to. Look
in the new Cabelas catalog p414 for 14 PAGES of samples of clever ways to get
up a tree safely and staying there comfortably. There is even a 16' tripod
stand with a platform, a ladder, swivel chair and guard rails that could be
used as a tune up tower. Remove the swivel chair and add a long telescoping
mast. These guys are clever with all their climbing and safety hardware.
There are 554 pages of hi-tech innovations for the outdoorsman that are
awesome. We could use the same creativity in Ham Radio Marketing and Design.
Ham radio catalogs are often very short!
I also agree that a 5 band 3 element quad with directors could pose a
problem on 10M with 12M elements. I previously pointed out that 12M (24.9
MHz) is 400 KHz closer to the harmonic relationship multiples of 3.5 MHz at
28 MHz. However most 10M activity is 28.35 MHz and higher which still gives
it about a 3.5 MHz+ isolation distance. Now the 3.5 MHz harmonic
relationship at 17M is 17.5 MHz and the actual operation is 600 KHz higher
and closer to 15M which suggests 17M elements should affect 15M even more
than 12M does 10M (if it really does). I have not heard of the same affects
on 15M. Perhaps it's the overall affect of the 5 bands is that there is this
querk on the higher 10M band only--if it's actually true? I added 6M and it
tuned up OK and even had the unusal affect beneficially of "actually
sharpening the vertical pattern" so that it was within one degree of the
Horizontal pattern with square elements. I have never seen this before with
monoband yagi's even 5 band square quads. It could happen with rectangular
shaped quads and will be looking for it.
Now the main design querk I've read of on TT only has to do with a 2
element 5 band quad using "REFLECTORS ONLY." To a large part it seems to be
more "conjecture" than "in actual practice." If some have actual experience
that can be duplicated I'd like to see it. I'll spend the time in putting it
in Eznec and perhaps even build it if there is evidence in Eznec something is
Now I will say again what I have found and will provide my Eznec data for
the serious students of "RF Reshaping." I actually spent many hours in
putting the XYZ data of the LB 2 element 5 band quad with the DE's all tied
together, printed out the patterns and "Print Screens" of the quad assembly
of wires with the relative current amplitudes shown on all the elements on
EACH band. The patterns SUCKS and RF currents on the off band elements is
EXCESSIVE--in particular on the DE's. The Eznec patterns verified EXACTLY
what I found on the air. I seldom had to rotate the beam after a CQ as the
answers came from all directions. I called a CQ DX on 20M pointed on Europe
and a rare China station "off the side" comes back. The frequency exploded
after I finished. I had many other examples of calls from the back. The LB
designer said "I was working them the long way around" (even at right angles
also?). He doesn't use antenna software either.
Now what I see in Eznec checked out exactly on the air. I've had many
Eznec patterns of other beams check out exactly for pattern and Z values
including a 3 element yagi tuned for absolute max gain of 10.2 dBi, 8 dB F/B
and 6 ohms feedpoint Z. It's the best 3 element I ever used but I feed it in
a very usual way also (they don't make 6 ohm coax).
I then did a copy of the LB quad configuration with individually fed DE's
with the usual massaging and all 5 bands had great patterns and there was
"Minimal RF" on the off band elements ON EACH BAND. I even fed the off band
DE high and low and the F/B actually improved on 2 bands. It totally blew up
the theory that the DE has to be resonant for the best patterns. All that
does is keep the reactance at low levels. If fed with open wire line into a
properly designed balanced tuner like Measures had in QST or the Johnson
MatchBox with my mods, it will match the Z "at the end of the feedline" and
maximum transfer of RF still occurs to the beam. One of the big advantages
of open wire line is "the most important place to match the Z is at the end
of the feedline and not at the antenna!"
Now since the patterns in Eznec for the LB I spent many hours on repeated
exactly ON THE AIR with a live beam I spent my money and time on testing, I
have to assume that the patterns of the "K7GCO Version" of isolated DE's in
Eznec--WILL REPEAT IN ACTUAL PRACTICE-AGAIN. Since others who have actually
built the quad and tuned it up without "the problem on 10M frequently
mentioned on TT," I have to suggest there is some misinformation being
perpetuated as a fact by those who have NOT done their Eznec work with
different configurations and didn't use "Reflectors ONLY." A "12M Director"
could be a problem on 10M acting to some degree as a 10M Reflector in the
wrong place. I will also spend the time to check this out in Eznec in detail
and report on it.
Based on my data I made the challenge of a bet I could make a 2 element 5
band quad also work on the air. So far no one has taken me up. How many of
those with all the "Conjecture" that there is a problem have actually paid
the price of time of in putting all the data into Eznec, purchased the LB,
used it on the air and modified it and found a problem even with isolated
DE's? I would like to see your data and will examine it very closely. If
your data is solid I'll eat Crow, drink some Old Crow and work on some new 4
Sq designs instead. You could save me a lot of time. Let me see the "color
or your money--and data". I'm just trying to find ANY solid technical
support I can duplicate for one more possible "TT Wive's Tale"-- no more nice
sounding technical theories.
ANOTHER BREAKTHROUGH: I should also like to add that in the 5 element 2
element quad configuration using tapered spacing of .125 WL, I and Cebik BOTH
found we got a bit more gain (around .5 dB) and 5-10 dB MORE F/B on most of
the bands than possible from a monbander of the same spacing. So the affect
of 5 interlaced quads even when slightly out of the 3.5 MHz harmonic
relationship, will "improve the performance." This is "very exciting stuff
guys." "Wake up and smell the extra performance." 5 band yagis can't make
that claim. I'm doing a series of configurations with wider spacing and
rectangular shaped elements as Cebik and Handelsman "IN ANTENNEX" have done.
It's "NO HOAX." Who know what lies ahead--real exciting stuff even from a 2
element quad? The yagi has about had it.
These are things you find out when you do your homework where others haven't
even opened the door. TT could be even more informative if all the
"anti-progress bias" would just go and stay away. There are lot of hams with
great new data and ideas who flately refuse to share it and get "flamed" as a
frequent term is often used. They share it with those who try to find
"what's right with it" first before riping it appart without even trying it
as frequently happens on TT. K7gco
> I can see where a 3 element 5 band quad could get real sticky and will
try it when I get time. These types of problems have been solved with wider
> spacing and that is worth a try. Variable Xc's can detune a parasite
> certain bands are used. My plan to use variable Xc's in each reflector
all ganged together driven by a selsyn on the mast has 2 ways of doing it.
Once the settings are found, adjust the set screws so the Xc's are all set
> gain for F/B. Or have all off band Xc's at random settings (within 180
> degrees) and detuned say on the low sides. On each band it is then
necessary to set the selsyn to a certain degree setting on each band.
The rest are all way off. There is a solution for just about any problem
crooked politicians if you are creative enough. This should isolate the
> even more. k7gco
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