Hi Tom,
looks like here we go again. I express some of my knowledge and information
based mostly on practical experience, as response to some claims otherwise,
and I get arguments that it can't be so because books say (and Tom knows)
otherwise. We went through similar exercises before on other topics. The
result usually is that Tom, gets quiet, maybe goes, does some work. Then
comes back after a while and becomes "guru" on stuff that I was accused to be
promoter of "pathological science" and not given credit.
I will do this one more response to your response. I do not appreciate being
put into the same bag with Fractenna Freak, I don't think I deserve that (nor
the others I mentioned).
In a message dated 2/7/2001 18:47:10 Eastern Standard Time,
w8ji@contesting.com writes:
> Hi Yuri,
>
> > It appears that some of the "new wisdom" is coming from the
> > software modeling "facts."
>
> Actually it comes from simple math that appears
> in antenna engineering books from the 40's and
> earlier.
> A quad is two 1/4 wl end-loaded dipoles stacked
> 1/4 wl apart.
> Stacking gain for two elements spaced 1/4 wl is
> one dB under **perfect** conditions.
That means, from the times before Quad and based on the math formulas, it
can't be? Just like Bumble Bee cannot fly? Or like hams cannot communicate on
"useless" shortwaves?
> > I just quickly modeled single Quad 1/4 wave/side loop vs. dipole
> > and I can get paper advantage of over 2 dB. So no folklore there.
>
> I cannot, no matter how I model it. I see one
> dB or less maximum gain over a dipole at the
> same mean height.
>
I guess that was the difference between Tesla and Edison. One could, one
couldn't. I can get in EZNEC close to 2 dB difference.
> In freespace, it is about one dB on the button.
> At some heights, it is less than 1 dB...and
> sometimes approaches zero dB. With more
> elements, the advantage is less at any height.
>
> Like any antenna, a quad "gets gain" by forcing
> a null in an area of significant radiation. That
> area is directly in line with the plane of the
> current maximas.
>
> If you place the quad at a height where ground
> reflection forces a null straight up, the
> horizontally polarized quad element provides
> minimal, if any, gain.
>
> If you place it at a height where radiation is
> maximum straight up, you get maximum advantage
> but at all practical heights that advantage is
> less than one dB for the two antennas compared
> at the same mean height.
>
> If the model shows more gain than theory
> (available since antennas began to be
> understood) predicts, the model is flawed or the
> comparison is unequal for mean height. Broadside
> array gain has been defined for many many years
> and the results have never been proven wrong to
> this day.
Well, then the model or software is flawed. I will verify that on real life
models on 2m and 10m. I am waiting for snow to melt.
> >(My 3 el. Quad beat 7 el. KLM Log Yagi on almost twice
> the boom on 2m.)
> > Quad (circular or delta) loops have larger aperture than dipole,
> > they have fatter vertical lobe and there is
> > suspicion that they pick up some of the "other" polarization too.
>
> I hear "aperture" used all the time to explain
> why one antenna is better than another.
>
> Aperture has NOTHING to do with physical size of
> an antenna. Aperture relates only to gain and
> frequency, not physical size.
>
Here you are contradicting yourself. You state that quad loop can have, lets
suppose only 1 dB gain, which means more gain. More gain, as you say means
larger aperture. Then you say, it can't have it. Which is then wrong? (I
didn't say that loops have larger apperture because they are bigger!)
> A two inch square antenna on 40 meters can have
> more "aperture" than a two mile square antenna.
> A fatter vertical lobe, for a given azimuthal
> beamwidth, means less gain (and more fading when
> multipath is involved).
>
> If any antenna picks up two polarizations, gain
> is always less than an antenna with the same
> pattern width that picks up only one
> polarization. If the antenna picks up both
> polarizations on a skywave path, or truly
> transmits both polarizations, fading is
> increased...not decreased.
>
> Quads do not pick up both polarizations because
> they are not constructed in a way that lets them
> to do that. Both polarizations
> are received (or transmitted) only when the
> antenna has dual elements or dual radiating
> areas with suitable phasing and
> polarization, like crossed dipoles in phase
> quadrature or a small loop and a small dipole on
> the axis of the loop.
>
> Quads pick up one polarization only, although
> that polarization might be skewed by feedpoint
> placement or feedpoint errors. Even
> if it is skewed, it is one polarization. It is
> just tilted.
Can you tell me what polarization has a quad loop that is closed, without
feedline attached? There might be a hint.
One experiment I made was; I wanted to see what gain if any has a quad loop,
horizontally polarized (fed at the bottom), diamond shape, in relation to the
vertical tower that would go near/through it. At about 1/4 wave from the
vertical tower, the loop exhibited about 5 dB F/B. Can the math calculate
that?
>
> > Quad loop has lower Q, wider frequency response, flatter SWR
> > curve, wider bandwidth.
>
> So do dummy loads.
>
That is very professional response. So the "dummy" quad has gain over dipole
(you admit that) and it is a dummy load? Can you 'splain that?
> > Quad loops provide more efficient match and RF transfer between
> > coax and antennas.
>
> That applies to UHF and higher where the coax
> diameter is large compared to the wavelength ,
> but not at VHF and below.
>
What has diameter of coax to do with match? More efficient match is due to
the fact that loops have a higher impedance. When we make an array out of
quad elements with higher impedance than in Yagis, less "transformer" is
needed, fewer losses. I managed design my antennas to have 50 ohm feedpoint,
no matching devices (which always have losses), better power transfer.
Another benefit is good soldered connections and solid copper wire loops,
rather than corroded junctions and "matches" as in aluminum Yagis.
> > http://members.aol.com/ve3bmv/Razors.htm Single Razor would
> > consistently beat 6 el. KLM by about 10 dB in real life tests.
>
> Are you really saying you "razor" has a measured
> gain of ten dB over a comparable size yagi?
>
I didn't say measured to 0.00001 dB accuracy. I said in real life tests. That
means real antennas, with real stations, with real (inaccurate) S-meters, but
being able to detect differences. Averaged over period of time, numerous
tests, various directions,
that was the rough result. BTW KLM 6 el. Big Stick showed also about 10 dB
advantage over 5 el. Telrex. This is what it means, real life, not with
scientists in white coats. This was the final verification of performance in
real life with all those imperfections that take part.
> Either something is wrong with the reference
> antenna or the test was seriously flawed. 10 dB
> gain over a 5 element yagi would require an
> enormous array!!!!!
I never said that, see above.
You have seen reports from 160m contest, and those reports have some meaning,
you are heard, you are worked, or nothing.
> > Some notable contesters use(d) loop
> antennas to cream competition
> > (W2PV,
> > K6UA, VE3BMV, K3ZO, KC1XX, VK3MO) and their
> experience confirms the
> > benefits of loop antennas. Those who know ..
>
> This sounds like the "science" used in the
> infamous "Fractal Run" threads of RRAA! "I
> worked "X" stations in "X" minutes so my antenna
> must work better than anything else"!
>
This is really low blow to all those who contributed so much to amateur
radio. Their results are immortalized in the contest results and records.
K6UA, K3JH had rotatable Quads on 80m, they had reports from DX and Americans
serving overseas, that their signals were more consistent and dominating at
varying conditions, where 3-4 el. Yagis didn't hack it. This is no "Fractal
Runs."
> Anyone who deals with statistics knows such data
> is meaningless, there are far too many variables
> other than gain involved in the results.
>
Not exactly, some meaningful data are obvious from contest results,
especially when comparing stations in close proximity, with other factors
being close, the antenna shows prominently, it is the tool that allows to
extend the propagation/conditions and allows working another layer of station
that others can't even hear. When I see my scores jump by 40% and I nail all
Canadian Records, I know I have better antenna than 1 dB. I don't care for
"scientific" analysis.
> > I am just now "investigating" loops with
> vertical polarization for
> > the
> > salty beaches, see what comes out. I am
> already getting 2 dB from
> > single loop over "mighty" dipole.
>
> I modelled a vertical dipole over perfect
> ground. The gain for low dipole heights was 7.3
> dBi.
>
> I did nothing but convert to a vertically
> polarized quad at the exact same mean height,
> and gain was 7.83 dBi.
>
> In this case, where everything is equal, the
> quad supplied a "roaring" .53 dB gain advantage.
>
> I placed the antennas at the same height over
> lossy ground, and they were equal!!!
Maybe the same difference as between Tesla and Edison :-)
For the situation of interest to me, I got 5.66 dBi from dipole and about 7.4
dBi from the loop in real life situation (not in the free space that I can't
get into for any money :-). That is closer to 2 dB than .53.
>
> 73, Tom W8JI
> w8ji@contesting.com
>
You know your stuff, I know (and saw with my eyes) my stuff. I enjoy some of
your stuff, but when I see something that doesn't jive with "my stuff" I try
to point it out (I am not alone as I saw), and then I get this...
Usually things are discovered and then "scientists" move in and figure it out
and explain it. So stand by...
73, Yuri, K3BU
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