Topband: Using the K2AV folded counterpoise at VK6VZ

[Guy Olinger K2AV]

Short Version:

VK6VZ wrote:

    [snip]

> ... a Marconi-T with a 66-foot vertical section over
> about 30 60-foot to 100- foot radials, had proved
> relatively ineffective...

> So far the results with the 3/8 wave inverted-L ... and
> the folded counterpoise, fed via [isolation transformer]
> ... have been startling to say the least.

> For the first time with a Marconi antenna from this
> location, I can work just about anything I can hear
> with similar reports.

> ... Having a 100 foot rather than 66 foot vertical section
> is clearly a big help ... the only reason I have this ...
> vertical section is because of being able to site the
> antenna [where it's] impossible to put down a radial field
> ...  along one side of the half acre block here.

    [snip]

G'day!  Thank you Steve for posting your results.

In the Long Version:

1) A NEC4 evaluation of Steve's old "Marconi T", supporting Steve's
magnitude of change.

2) Let's go visit some small lots.

3) 3/8 wave inverted L over an FCP, NEC4 compares it to reference gold
standard vertical over "average dirt", partly explaining Steve's success.

---------------

Long version:

Thank you, Steve, for sharing on the reflector your positive experience
with a 3/8 wave end-fed over FCP.

I think there is a lot about "restricted circumstances" that some either
don't understand or find hard to identify with.  Your experience is
remarkably similar to mine, and to that of many others.

You said antenna A had to be down to erect antenna B.  Use of  the FCP as
the counterpoise in antenna B allowed you to construct in the only place
where a 3/8 wave was possible.  You patterned your new antenna after one
you read about that worked well, and got excellent results yourself.  And
then you got on here and told us about it.  NOTHING the matter with that.
 Nothing AT ALL.  That's about as ham radio as it gets.

Looking forward to working you on Top Band.   Please do enjoy the new
antenna.   And you're certainly welcome.

-------------

It is really not that hard to understand Steve's success, or his prior woes.

Full size dense and uniform all around radials are the gold standard, the
creme-de-la-creme.  Really.  And it is REALLY NICE to have the land to do
that stuff.  Full size dense and uniform all around always works well with
a quarter wave vertical radiator on top.  It's STILL what you do for best
results if you've got the room for it.

The EVIL LITTLE SECRET some aren't onto yet is why and how quickly the
radial performance degrades using SHORT, IRREGULAR and/or SPARSE, CHOP-JOBS
on full size dense and uniform all around.

For a lot of the layouts I have seen or heard of, short, irregular and/or
sparse chop-job is the correct description, for sure.  But they were done
that way because there was NO ROOM on the property to do anything else, if
you were doing radials.  That is the oh-so-common situation.  You can get
away with more chop if you have really great dirt.  If you have bad dirt,
the chop job throws away S units.  Plural intended.

With additional information from Steve, my NEC4 comparison of his "Marconi
T" over chop job radials over awful dirt versus gold standard shows the
difference at 10 degrees takeoff is 6-8-10 dB depending on what assumptions
are used.  That result certainly gives no reason to disbelieve Steve's
anecdotal reports.

The FCC talks about 120 times 0.4 wavelength radial fields.  430 foot
diameter circle.  :>)  60 times 0.25 wavelength radial fields is what we
hear about for hams.  250 foot diameter circle for 1/4 wave radials.  I got
no dog in the fight about which radius is better, or whether 60 is really
30, let someone else argue.  But either way, does anyone have a feeling for
the magnitude of mental disconnect when we talk about the little guy on a
small lot, mostly used up by a house, trying to do a 160 meter antenna, and
in the same breath bring up radials requiring 250 foot diameter circles to
do well?  The jarring incompatible necessities seem to go right over quite
a few heads.

In a series of postings some weeks ago it was suggested by some that FCP
users should all get a comparison to two opposed 1/4 wave radials by using
some clip leads on their FCP and extending the wires out to 1/4 wave on
either side.  That would get you two opposed 1/4 wave raised radials, true.
 To be fair they were suggesting this in order to get a common benchmark to
tie into other comparison listings.  However...

Since the FCP isolation transformer has deliberate residual inductive
reactance to help balance out deliberate residual capacitive reactance of
the FCP, one would need to change out the isolation transformer for
something else to use with the resonant 1/4 wave radials, muddling the
results with apples and oranges issues.  For example, one could wind up
only measuring energy difference lost on coax shield common mode by not
using the isolation transformer, with no way to attribute the source of the
loss.  But that aside, there's something much more basic.

Talking of one typical FCP user in Texas, if he extends the FCP wires to
1/4 wave either side, on the west he'd have to negotiate with his next TWO
neighbors to run wire across both back yards.  And as he's on a corner
boundary lot, the east wire would be across the subdivision boundary
street, across the boundary park strip, over the fence and into the
southbound right driving lane of a limited access parkway.  At my place I
could put up the north extension, but the south extension would be out in
the service road right of way for US 64 Highway.   Try negotiating
something with NCDOT.

To illustrate matters of scale, in the Texas subdivision that I mentioned
above, according to Google Earth, clearing property for the FCC 430 foot
diameter circle would require demolishing 23 houses, give or take a couple
properties.  See  29.58672   -98.52185   Count them yourself.  Reducing
that to 1/4 wave radials and a 250 foot circle reduces the carnage to a
mere 14 properties, give or take.   There are places with even higher
densities, particularly in Europe and Japan.  See the mental disconnect yet?

I know far more hams living on property that can't support 160 meter full
size dense and uniform all around, than can.  Of those who can't, most are
FAR short of the circumstances needed for radials.  And it's always been
that way.  Look at the older "middle class" neighborhoods.  Small lots and
smallish houses are the norm.  These days you have big houses on those same
small lots in HOA neighborhoods.  Still mostly small lots, with even less
room available for such things as radials.

One would think that in the 75 years since the watershed 1937 Brown, Lewis
and Epstein (BL&E) study on radials,  we would have paid a lot more
attention to small-lotters, given their predominance.  FCP SHOULD have been
invented by some expert ham about the same time they turned off the LORAN.
 For shame, whoever you were, that went to the movies or the bowling alley,
instead of inventing the FCP.

>From the photos in the BL&E study, those RCA guys were testing in a huge
flat farm field of black dirt, easily flat out past a mile, large enough to
contain quite a number of replications of that entire Texas subdivision.

For the study however, BL&E QSY'd from their lower BC band frequency all
the way up to 3 MHz, beyond high broadcast band, beyond our 160 meters, and
beyond two point anything MHz, all skipped as too much to work with.  Two
much wire, too much time to bury radials, daily distance of researchers'
walking back and forth, size of radiators, yada, yada, who knows what all
too much.  I'm sure the reasons were all practical as nails.  Apparently
that kind of study is difficult, a lot of work, and needs a lot of space,
even at 3 Mhz.

And those guys were PAID professionals, RCA employees, doing it as work
assigned by RCA. They had materials paid for by RCA, had RCA-blessed
weekdays to work on it, in addition to use of the huge field, probably
negotiated FOR them by yet another RCA employee.

But here on TopBand in 2012, do we expect that kind of research from
hobbyists with tight funds, meager room, using precious spare time, before
they can come on TopBand and happy-post about how well their new antenna
works?

RBN scores, breaking pileups, watershed changes in contest scores, or being
able to easily work somebody after years of trying, any number of anecdotal
startling improvements, are PLENTY good enough reason to post happy
thoughts on a new antenna.  Thank you, Steve.

Or is the issue really the FCP?  If someone is trying to keep the FCP
concept from spreading or trying to talk it down, they're  just the least
bit late.  The FCP is published in the National Contest Journal, and it's
been out on the web **  for quite a while.

The web page detailing the FCP has 39,000 hits from all around the world.
 After some two years to become really old news, the page is still getting
30 hits a day.  Imagine, old news getting 30 hits a day on a subject so
esoteric and niche as a small lot counterpoise for a 160 meter ham antenna.
 Must be some heretofore untapped demand, eh?

FCP is clearly running on its own energy by word of mouth.  I still have a
busy correspondence going on with new FCP adopters, with only a small slice
of the hubbub ever showing up here on TopBand.  I find it hard to get a
correspondent to post an aspect of their success on the reflector.  I don't
really know why they don't.  I don't ask.  I suspect that when they get it
working, they go back to their lives, having used their allotment of
precious spare time.

I have included some detail on the 3/8 wave L over FCP as used at VK6VZ and
K2AV:

Important:  Note that the following is NOT offered as applying to
conductors over a quality radial system, as explained at the end.

Already given that the 3/8 wave L's  horizontally polarized component is
useful for dawn or dusk propagation, and that the high angle radiation from
the horizontal can fill in skip zones at night for "on continent" QSO's, a
further benefit is moving the current maximum to the top of the vertical
radiator.  In a 3/8 wave L, roughly equal H & V wires, the horizontal
functions as 60 to 70 degrees of unbalanced radiating top load, and the
current max is in the highest 1/16 wave of the vertical wire.

I ran some number of comparative NEC4 models, various L over FCP vs. each
other and vs. a reference 1/4 wave over 120 x 1/4 wave buried radials.  All
used so-called average dirt (.005/.13).

Versus a 1/4  L over FCP, the 3/8  L over FCP does several things, 1)
 lowers the current in the counterpoise, reducing it's contribution to the
loss bucket, 2) moves the mass of the current up 80/90 feet in the air,
reducing the vertical radiator's field intensity in the immediate area dirt
below, reducing that contribution to the loss bucket, 3) improves the
pattern at ten degrees elevation, 4) increases the max gain in the pattern.
 Varying the dirt in the comparison just shows that vertical antennas over
great dirt do better, which we already knew.

The degree of 3) and 4) can be increased by doing the 70 degree top load in
a fold or folds that partially or considerably cancel the horizontal
component.  The NEC4 model of a mechanically simple 70 degree 65 foot out
and back "skinny pennant" top load, with a 100 foot vertical section over
FCP brings the max gain to within 0.6 dB of the reference 1/4 wave over
buried radials.  It's within 0.8 dB at ten degrees.  The result is still
without the pure vertical's straight up deep null that can create
unnecessary skip zones.  Going out only 65 feet may be physically useful in
a given circumstance.  Other triangular folds for a 70 degree top load can
be supported by the vertical's fastening and keep the top load inside the
FCP's +/- 33 foot linear footprint.  This last has elevation and azimuth
pattern (not gain) essentially identical to a vertical of the same height
over radials.  Of the variations I have modeled the skinny pennant top load
is the closest approach to the reference 1/4 w over 120 x 1/4.  The 100 V
100 H using the same dirt is down another half dB from the skinny pennant.

But still, that's within a fat dB of the gold standard.  And compared to
the 66 foot T over chop-job radials, further given that gold standard full
size dense and uniform all around radials handle very poor dirt much better
than chop job radials, you can understand Steve's "startling" change.  It
all fits.

You DO gotta have the big trees to get 80-90-100 foot vertical runs.  But
you can still put it up in a skinny footprint and you don't have to attempt
radials you can't possibly do right, or at all.  How about the lot with a
100 foot tree right next to the house AND the neighbor's house with the
tree split by the  property line.   FCP plus 90 foot vertical with 70
degree triangle top load fits.  FCP plus vertical with skinny pennant top
load maybe fits.  Maybe 3/8 L fits.  Guys on small lots can do this stuff.

Also, as I hear proposed to me a lot, the up high current max might help
the antenna to "see over" lossy clutter at the ground level so lower
takeoff angles have to go through less forest or construction to get clear.
 This invokes the ancient controversy about how much loss in taking off
through a forest.  If you take the worst estimates of that loss, centering
most radiation 90-100 feet up intuitively offers a large "see -over"
improvement over a gold standard vertical at the ground, an advantage not
book-kept in comparative NEC4 models.

Although this has always sounded plausible, it seems nearly impossible to
prove, because standing-man-with-meter unfortunately is also
standing-man-standing-on-the-ground and the phenomenon is well overhead.
 Considering often violent local variation in local soil characteristics, a
true test with all elements controlled would require
sitting-man-in-helicopter-with-meter, before and after cutting down the
forest, except for the tree supporting the antenna.  The "see over" idea
just sticks around in the back of one's mind (including mine) and won't go
away.  But it will have to remain merely an unproven temptation to antennas
with up high current max.

And so maybe a 3/8 L over FCP owner with a consistent really loud signal
will really never be able to prove why.

-----------

Caution: Remember that inverted L's with the bend supported by a close
tower are a special case with possibility for severe loss.  This is a
separate discussion not specific to FCP's, but as easily affecting an FCP
based inverted L, as an inverted L over radials.

-----------

With RADIALS, full size dense and uniform all around, various authors
question any positive benefits of moving the current max up the wire, and
some conclude that moving max up the wire reduces performance.  These are
not conclusions from my work, and I have no dog in that fight, though my
gut feel is they are probably right.  This outcome is also suggested in
models because moving the max up the wire over radials reduces the degree
of vertical field vs. radial field cancellation in the dirt underneath.
This is seen in near field listings as higher net field data in the dirt
underneath the radials, therefore more loss.  So current max down at the
feedpoint appears to be optimum over good radials for radiator heights
commonly attempted by hams.  This is just to underline that the
move-the-max-up-the-wire text in the earlier paragraphs is ONLY intended
for 3/8 wave inverted L over FCP.

One would think that if 3/8 wave L's over radials (high up current max)
were an improvement over straight 1/4 wave or 1/4 wave L's over radials
(down low current max), that 3/8 L's over radials would be seen more
frequently and bragged about.

3/8 wave L over radials and 3/8 wave L over FCP create pattern and loss
with the same physics, but have quite different details for losing energy
in the ground, not to be confused with one another.

-----------

73, Guy.

** http://www.w0uce.net/K2AVantennas.html