What a wonderful test it would be for Tom and Guy to do this analysis. I
would love to know the results.
----------------- Wes Attaway (N5WA) -------------------
1138 Waters Edge Circle, Shreveport, LA 71106
318-797-4972 (Office) - 318-393-3289 (Cell)
Computer Consulting and Forensics
-------------- EnCase Certified Examiner ---------------
-----Original Message-----
From: topband-bounces@contesting.com [mailto:topband-bounces@contesting.com]
On Behalf Of Guy Olinger K2AV
Sent: Tuesday, July 31, 2012 2:29 PM
To: Tom W8JI
Cc: topband@contesting.com
Subject: Re: Topband: FCP model
Hi Tom,
I was hoping that you would clarify your earlier remarks.
The FCP is not resonant because it is designed specifically to
self-cancel fields, not to be resonant. Said another way, it's
DELIBERATELY not resonant. The May/June 2012 NCJ article on this
counterpoise explaining how and why can be found at:
http://www.w0uce.net/Olinger_FCP_article_as_published_in_NCJ.pdf
Not trying to put you off, but repeating the article in a TopBand post
seems inappropriate, and doesn't come with the pictures.
Your assessment of the roughly opposite and equal reactances is
certainly correct, as are the toroid vagaries. I would expect no less
from you. So far that toroid issue hasn't mattered. People are pruning
all shapes of inverted L, or even inverted U, into somewhat longer
than 1/4 wave wires, to get the zero reactance point adjusted. The far
larger variable is the shape and distance of the wire from ground. It
turns out to be a lot like pruning a dipole, every situation is
different. The longer wire, and the 157' length of the FCP raises the
R at zero reactance, which is useful.
See:
http://www.balundesigns.com/servlet/the-108/1-cln-1-High-Isolation-balun/Det
ail
for the commercial version FCP.
The choice of the #2 powdered iron was suggested by Sevick's work,
picked for low loss with voltage across the winding, and has worked
out well. Yes, the #2 beasties DO vary on inductance with turn
inconsistency. But particularly on 160, the 20 bifilar turns of #14,
in standard thickness teflon sleeve, exactly fills the inner diameter
of the toroid. Pretty hard to get too far from uniform. Makes one
wonder if the whole thing might have been done on purpose.
The commercially made isolation transformers, and well-done hand winds
come in at 19 uH consistently on my instrument. Balun Designs 80m
version is uniform, of course, and we have 80 meter four squares out
of these in what otherwise would be impossible circumstances. I
figure it's just a matter of time until we see 160m four squares over
FCP's in less space than required by a single commercial method
vertical. I tell people to use the commercial isolation transformer
for a four square, to keep them all the same.
The evidence of "working well" is largely anecdotal but quite
compelling, and so far consistent. It may be that a 3 dB down
"failure" in a comparison against a commercial grade installation is a
brilliant success where 160 was otherwise impossible.
There are documented high end successes in contests with FCP's, and
very decent RBN signal-to-noise readings. The PDF includes some of the
compelling anecdotal evidence. I can put you in contact with my
Detective Sergeant neighbor who can verify aspects of one of the
stories in the article. He thought it was hilarious that the acme of
success was signalled by knocking neighborhood AT&T Uverse 3800
gateways off sync and into reboots. As you might imagine, I had mixed
emotions.
And the really big success is that it is working well for small-lot
hams that have zero possibility of doing anything else even remotely
efficient. That is really what it's all about. That it works well in
other situations, and that someone even THINKS of comparing it with
commercial standard antennas is totally gravy on the potatoes.
The venue for an exhaustive comparison is extremely hard to do without
funds or a venue controlled by a ham with the space and an existing
commercial gold standard vertical in a spot without miscellaneous
interfering resonances all around, and with lots of lab grade
measuring equipment. Building up MF antenna academic-grade
side-by-side tests from scratch is a staggering task without
commercial funds, or a fortunate venue.
It strikes me that chez W8JI might be one of those fortunate venues.
I would be more than happy to travel to Ga with materials to put up a
comparison supervised by both a careful skeptic and an advocate. The
opportunity to do an academic grade comparison with known good
antennas, including an L and other vertical radiators over the FCP,
would be irresistible. Wonderful NCJ article material, however it
comes out. "The Great Georgia FCP Shootout" :>)
My sealed-envelope-in-advance prediction is that an FCP shows 2 to 3
dB down from one of your good verticals. That's simply expected,
mainly because the FCP MUST lack the ground field cancellation found
in commercial grade radial fields. If the FCP was better than that,
there would be quite the conundrum or two to explain, and given the
aggravation of putting down commercial grade radials, there would be
little reason to use the copper or the acreage anywhere. But you are
NOT hearing ME as an advocate of an FCP replacing dense and uniform
all around 1/4 wave radials. Gold standard is still the gold
standard. I'm mostly trying to help the N3ND's and VO1HP's of the
world who are well settled in beautiful small lot settings, and who in
spite of that think they want to operate on 160.
73, Guy.
On Tue, Jul 31, 2012 at 10:19 AM, Tom W8JI <w8ji@w8ji.com> wrote:
> I did a little more looking at the FCP system. I said this:
>
>> By the way, a check of voltages shows the voltage from radial center
point
>> to ground is 226 volts RMS at 1500 watts when four radials are used. This
>> is
>> for infinite isolation. While this clearly shows we need a common mode
>> choke, as most elevated radial or sparse radial systems do, why does a
>> voltage this low demand an isolation style transformer?
>
> The answer to this question is quite evident. The 66-foot wide FCP system
is
> not even close to resonance on 160 meters. It appears the capacitive
> reactance introduced by the FCP, being tuned well above the 160-meter
band,
> must be compensated.
>
> -2 mix iron toroids have notoriously high levels of flux leakage.
Inductance
> has varied as much as 2:1 in cores with the same number of turns,
depending
> on if turns are spread or compacted in one core area. This makes it
> impossible to determine actual core inductive reactance added to the
system,
> but it should be a few hundred ohms.
>
> This more-or-less few hundred ohms inductive reactance is about right to
> correct the counterpoise being out-of-band.
>
> It is pretty clear the reason the FCP requires an "only this one works"
> special matching transformer is because the counterpoise isn't actually
even
> resonant inside the band. The counterpoise is resonant above the band, and
> the leakage reactance (whatever that happens to be from winding style)
that
> limits coupling and winding reactances add enough inductive reactance to
> load the system back into the band.
>
> With a little reverse engineering, I've answered my own question. A
> traditional line isolation device, while working perfectly fine with a
> RESONANT counterpoise on a resonant length antenna at the current maximum,
> will not work on the FCP for very obvious reasons. The FCP counterpoise
is
> not resonant, and requires insertion of considerable inductive reactance,
to
> become resonant as a system.
>
> The capacitive reactance FCP and inductive reactance matching transformer
> form a tuned system. The combination acts like a single short-length
folded
> inductor-loaded "radial". This is why voltages are so high, and why only
one
> particular coupling system works.
>
> Now here is a question, Gotham vertical measurement methods aside. (see
> http://www.w8ji.com/gotham.htm )
>
> Has anyone actually measured one of these systems in a meaningful way
> against a proper reference antenna?
>
> 73 Tom
>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|