[Antennas] CCD antennas

[Jim Shaw]

Kevin, Bell, et al
In addition to the ARRL Compendium #2, the ARRL Compendium #3 has two
articles on CCD antennas. They are as follows

Controlled Current Distribution Antennas
131 The CCD Antenna - Improved, Ready-to-Use Construction Data
    Harry Mills, W4FD, and Gene Brizendine, W4ATE

134 Controlled-Current-Distribution Antenna Performance: By Analysis
    Bill Shanney, KJ6GR

I have no experience whatsoever with CCD antennas so I will just attempt to
summarize the points made in these two articles as well as the ones made in
the 2 articles in Compendium #2.  Here goes.

The overall length of a conventional, center-fed dipole is 1/2 WL (2 1/4 WL
elements each side of center).  The length of a CCD is a full WL, 1/2 WL
each side of center.  In a CCD, capacitors are inserted in series, spaced
regularly along the length of the wire.  All capacitors are of the same
value.  The value and the spacing can vary widely.  In general, the more
capacitors the better.  The longer wire in a CCD element means there is too
much inductance (due to the wire) for it to resonate so capacitance is used
to offset that in order to resonate the antenna.

This is desirable because in a standard dipole, current is greatest at its
center and least at its ends.  Voltage is distribution is just the opposite.
In a CCD, capacitors change the current and voltage distribution, making
variations in both parameters less than in a standard dipole (more even
along the entire length of the wire) while also leading to a higher feed
point impedance by about 4 or 5 times.

In a dipole, maximum 'pumping' of signal into space occurs at the current
maximum (the center).  In the CCD, there are many current peaks - at every
section - thus the entire length of the wire is used to radiate signal
although the peaks are smaller than the single peak in a dipole.  This tends
to narrow the width of the radiation lobes off each side of the CCD antenna
thus enabling greater gain than that of a dipole.

Some of the major CCD advantages and disadvantages listed in the articles
are:
1 Greater gain than a dipole (but exactly how much greater since it is not
quantified)
2 Reduced, or eliminated, end effect radiation
3 Higher antenna feed point resistance (300 to 370 ohms)
5 A vertical CCD has a lower angle of radiation
6 CCD works well lower to the ground than a dipole (e.g. 8 feet)
7 CCD exhibits good broadband characteristics (e.g., will cover 80 & 75
meters without a tuner)
8 It is less lossy than a standard dipole
9 Lobes and nulls are very strong, very pronounced
10 It costs more to build due to the extra wire, capacitors, and labor
11 It takes up more space since it is physically a full WL long

Additional notes:
1 It is very important that all capacitors used be very close in value.  5%
tolerance is suggested.  Best are 300V 5% silvered mica since they have low
loss, a high Q, and are rugged.  Also good are polystryene capacitors.
2 It was patented by Harry Mills - patent 3,564,551
3 A 1:4 balun is recommended since the impedance is about 350 ohms
4 Feed it with 450 ohm ladder line or with 300 ohm foam ribbon

Hope that helps clarify things for you.  Was an interesting bit of reading
for me as I had not really investigated CCD antennas before.  Don't plan to
build one myself but will be interested in hearing feedback from others who
do.

73 de Jim WA6PX
JGShaw@Alumni.HAAS.org

-----Original Message-----
From: Kevin Nathan [mailto:k7rx@attbi.com]
Sent: Wednesday, December 25, 2002 11:05 AM
To: Jim@ShawResources.com
Subject: RE: [Antennas] CCD antennas


Hi All,

Unfortunately, I am blind and none of these antenna compendiums are
available in any kind of alternative format of which I am aware.  Would one
of you please explain kind of how one of these antennas would look and how
you would assemble it?

thanks very much and very 73 to all.  Have a wonderful Christmas.

Kevin, K7RX :)