Re: NEC-LIST: More on the CFA

> Jack, I spoke with Kabbary, Stewart and Ron Nott Sunday night in
> Vegas, on a mission to see if there were some way to resolve the NEC
> results with their claims. Brian says that NEC could model the CFA
> correctly if all the small current elements in the array were
> replaced with voltage elements. He even stated that he would be
> willing to write a version of NEC2 that was based on voltage
> elements instead of current elements. He implied that it would be a
> quick and easy project.
>
> Any thoughts?
>
> I suggested that if a working one kilowatt CFA operating on 1610 kHz
> with an experimental permit from the FCC were available in the USA
> for open evaluation by any antenna consultant or academic with a
> field intensity meter, then his CFA might begin to gain some
> acceptance. Kabbary invites anybody who is interested to visit the
> CFA sites in Egypt, but this is a bit inconvenient for most of us;
> besides these stations are operating with programming most of the
> time, and not readily available to go off the air for any
> significant length of time. I certainly would not want to travel
> there only to be told that is was not a good time for a visitor to
> stick his operating impedance bridge in circuit, etc.
>
> Grant Bingeman

Grant,

Concerning NEC and voltage sources, I have already done this. For
EZNEC one can choose Voltage or Current sources, and for some
antennas, e.g. the off-centre fed dipole, particularly if the
transmission line is a part of the wire model, this makes an important
difference.

For the CFA antenna the FS at 200 m employing Voltage Sources is 159
mV/m (Pt = 1000 watts), compared with 156 mV/m --- but there is a
curious (interesting) difference.

With Voltage feed I have to reverse the sign of the phase of the
Sources, +45-degrees and -45-degrees, I think I noted this before, for
the very short monopole and the disk respectively (the phases are now
like that reported by Hately et.al [1991]). For Current Sources the
phases are -45-degrees and +45-degrees respectively. But (perhaps)
even more curiously the values of the resistive component of the
impedance reverses, 177.6 ohms and -189.5 ohms for Voltage feed;
compared with 189.4 ohms and -177.5 ohms respectively. I had not
noticed this before.

The CFA is indeed a curious beasty.

*But with Voltage Sources I see still see currents on the wire-grid
model*. NEC is based on currents on wires.

I await with interest seeing a copy of Brian's paper.

I copy below a message I sent out yesterday --- because I note I left
you off the list. However I am not sure whether you wanted to get
involved in modelling the CFA.

I found out the reason why you were not able to open my EZNEC Antenna
file for the CFA, by sending the file to myself. I am connected to
the the the INTERNET (EUDORA) by a Macintosh --- and apparently I can
receive EZNEC Antenna Files, but I cannot send them (???).

To receive files I copy to a diskette formated for PC, and then copy
the file from the diskette to my EZNEC Directive. Works great --- but
not the other way around. Why??

If you would like to have the file let me know, and I will ask a
colleague to send it using a PC (Encoded MIME). My Macintosh will
Encode in Uuencode or BinHex, neither seems to work.

73, Jack, VE2CV

PS

I am copying this to the NEC-List, but I think we should correspond
within a smaller Group if we are addressing details of modelling ---
if others get up to speed.

********************************************

>Date: Tue, 20 Apr 1999 12:21:35 -0400
>To:<KLysiak_at_swri.edu>
>From:john.belrose_at_crc.ca (John Belrose)
>Subject:Re: CFA
>Cc: Max J Schmitt <mjschmit_at_bellatlantic.net>, Sylvio Damianni
><sdam_at_u-net.com.br>, Tay Roger-esys05 <esys05_at_email.mot.com>, Ashley
>Bicknell <abicknell_at_rfs.com.au>, Alberto Fassio <afassio_at_iol.it>
>
>>From the desk of Keith Lysiak
>>
>> Jack,
>> Nice to talk to you again. I chaired the session at ACES. I have
>> some modeling experience and a reasonable amount of computer power.
>> I am reasonably handy with NEC, FDTD, and UTD. I have the
>> capability of modeling up to 5400 segments with NEC 4 and 16 million
>> cells in FDTD. I also have a number of utilities that will allow me
>> to quickly mesh large objects. If you could FAX or e-mail me the
>> electrical details that you have on the CFA, I would be willing to
>> assist you in your modeling efforts. I could supply color graphics
>> of planer cuts of E and H fields around the antenna components. I
>> could also attempt to do some modeling with FDTD which is definitely
>> a complete (although discrete) solution of Maxwells equations. I
>> have not found Maxwell's equations to lie yet. I would be working
>> on my own time, so results would be slow coming, but we approach the
>> problem with several methods, I think we can answer some questions.
>>
>> End of Message
>> Keith A. Lysiak, Ph.D
>
> Hello Keith,
>
> Yes, I was pleased to meet you at the ACES Conference, and we did
> find a few moments to share interests..
>
> So far several antenna scientists/engineers (on the NEC-List) have
> expressed an interest in CEM modelling the CFA --- see Cc: above.
>
> Max started his modelling much earlier than I did, and he has given
> a summary result of his early analysis (in part posted). I do not
> have details of his model --- but his computed results are very much
> different from mine.
>
> With all your computing capability, do you have Roy Lewallen's
> EZNEC/Pro program, because if you do I could send you my file as a
> starter? EZNEC-Pro can accept NEC files (so my manual says), but I
> am not sure whether an EZNEC file can be read by NEC. As I said in
> my last technical note (Thursday) on the subject I think I now have
> a very good *wire-grid* model. However, I would not expect any
> different result from whoever used my model.
>
> So, perhaps what we want is a disk modelled as a solid disk --- or
> an analysis by a program different from NEC-4.
>
> My next step could be to simulate the actual Egyptian antenna, as
> best I can from the details given in the Hately et.al [1991] paper
> --- viz. put the CFA on the roof of a building with its wire mat
> ground plane --- and add a 75 m tower tuned and not tuned at varying
> distances from the CFA.
>
> But before I do further work I will await seeing a copy of the
> Stewart and Kabbary NAB [1999] paper; and Alberto Fassio's "proof of
> performance type" measurements in Italy.
>
> I will await your reply, and, at least send you a FAX showing my
> model of the CFA, and a print out for my analysis.
>
> Perhaps we should establish a mini-list of those seriously modelling
> the antenna, or experimentally measuring performance.
>
> Regards, Jack

************************

From: "Jack L. Stone", INTERNET:jack_at_antennex.com
To: [unknown], INTERNET:readers_at_antennex.com

Date: 4/18/1999 10:57 AM

RE: CFA Lives in Florence!

Dear readers:

For those of you who have been following the eXperiments with a Ham
version of the CFA, we are pleased to announce that Stefano Galastri,
IK5IIR of Florence, Italy has a working version of the CFA on 7 MHz
and made many contacts with strong signal reports as far as 5000 Km!
Fellow countryman, Guglielmo Marconi would be proud of Stefano who is
among the first of our readers of the CFA 9-part series in previous
antenneX issues to have overcome the difficulties of duplicating the
matching network and the tricky tuning methods described.

Stefano has documented his CFA in great details and numerous close-up
photos for an article to be published in the antenneX upcoming May
1999 issue.

Also, Jean-Marie, VE2JNG of Quebec has sent us beautiful photos of his
CFA project too. He is working on incorporating the matching network
and tuning procedures used by Stefano & we hope to publish an article
about that version in the June 1999 issue of antenneX.

Best regards, Jack

Our Web Site: http://www.antennex.com/

Jack L. Stone, Publisher
antenneX Online Magazine
c/o Texas Capital Management
P.O. Box 72022
Corpus Christi, TX 78472

E-Mail: jack_at_antennex.com
Voice: 512.855.0250
Fax: 512.851.8278

************************ end of message

_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
Communications Research Centre
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2779
FAX 613-998-4077
e-mail <john.belrose_at_crc.ca>
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Received on Wed Apr 21 1999 - 15:53:42 EDT