NEC-LIST: CFA and the Hately advertisement

John Crabtree wrote:
>
> Hello Dr. Belrose
>
> Recently I saw a post on the rec.radio.amateur.antenna newsgroup
> regarding the NEC list and the work that you have been doing
> modeling the CFA antenna. I have visited the archive and found it
> most informative.
>
> Have you seen the June 1999 edition of 'Electronics World' where
> there is an advertisement from Hately Antenna Technology where they
> say, among other things ?:
>
> "The Isle of Man will soon be the site of the first UK high power
> CFA for broadcasting. The IOM Government has announced that the
> Isle of Man International Broadcasting Company Ltd has been selected
> to be allocated the licence for the 279kHz Long Wave broadcasting
> station. The company's application was attractive because of the
> minimal visual impact of the CFA only 30 metres high instead of
> rival submissions using conventional masts of 260 metres high.
> Additionally the lower voltages and *almost zero induction field*
> (highlight is mine) of the CFA provides enhanced safety and minimal
> EMC problems."
>
> Mama mia! I can only conclude that this CFA business is getting out
> of hand...
>
> Best wishes
>
> John Crabtree
> Edina, MN

To Interested Readers of NEC-List:

The advertisement notes that three progress milestones have been passed:

1) The NAB '99 Conference paper;
2) The Isle of Man installation; and
3) That there are wide-ranging discussions on the Internet Magazine
"Antennex" (http://www.antennex.com), and many amateurs in radio are
successfully using a small size 80M version of the CFA (it is 2.6
times smaller, dimensions in wavelengths, compared with the MF antenna
I have been modelling). The wire grid ground plane is only 1m x 1m
which makes it easy to mount on a high tower.

My view: the higher the tower the better --- perhaps one that is
resonant.

Brian Stewart keeps telling me that the only way to be convinced is to
build one, and measure the (great) performance myself. I have been
corresponding with him re a recommended version I might build for 3750
kHz --- which turns out to be the Antennex CFA. I propose to
collaborate with Brian --- I want to stay at arms length from the
Antennex group.

The phasing and tuning network is certainly nothing like the
simplicity suggested by Hately et.al. conference papers --- on which I
have been commenting.

A transformer (centre tap grounded) feeds the E plate and the D plate
out of phase. The lead to the E plate contains a parallel resonant
circuit (a 5.4 microhenry toroidal inductor and a variable 400 pF
capacitor); the lead to the D Plate is an L-network, a variable 400 pF
capacitor to ground and a series 5.4 microhenry toroidal inductor.
There is no suggestion that one adjusts the only tuneable components
(the 400 pF capacitors) for equal currents or voltages in phase
quadrature --- one tunes for maximum FS. But this is a CFA intended
for construction by radio amateurs. Apparently the capacitors can be
ganged --- approximate value for the 75/80M band is said to be 330 pF.

The Hately Antenna Technology advertisement has given me the e-mail
address of Maurice Hately, so I have written him --- but I just sent
my message yesterday.

73, Jack
Received on Wed May 19 1999 - 19:50:59 EDT