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[TowerTalk] C3S question

To: <>
Subject: [TowerTalk] C3S question
From: (
Date: Wed, 4 Apr 2001 12:05:00 -0600
I must not have been fully awake when I wrote my response.
There are 4 different versions of the C3 series antennas.

C3    DE has 20, 15, and 2- 10M elements, plus
        10M DIR, 15M REF, 20M REF on an 18 ft boom
C3E  same as C3 + 10M Reflector

C3S  DE has single 20, 15, 10M elements plus 
        10, 15, 20M REFLECTORS on a 12 ft boom

C3SS same as C3S but has linear loaded 20M elements for reduced size

To my mind, the C3S is the ultimate in elegance and simplicity.
It should produce performance equivalent to 3 separate 2L monobanders.

Note that peak gain for 2L Yagi's is close to 7.0 dBi.
Unfortunately, peak gain and peak F/B seldom occur
with the same spacing and tuning.  Typically, gain
is reduced by up to 1 dB to achieve better F/B.
This applies to MOST Yagi designs regardless of
number of elements.

MONOBAND Yagi comparison guide:

Boom        Elements    Gain            F/B
Length                  dBi             dB

.15 WL          2       6 - 7           5-15

.25 WL          3       7 - 8           20 - 35

.35 WL          3       8 - 9           15 - 25

>From this chart it is apparent that a SHORT BOOM 3L
Monoband Yagi has only 1 dB gain over a 2L Yagi and
a WIDE BOOM 3L Yagi has 2 dB gain over a 2L Yagi.

Tribanders with 3 or more active elements per band
are necessarily a compromise, sacrificing gain for
size, F/B ratio, and SWR.  TRAPPED tribanders also 
sacrifice BANDWIDTH.  It should be clear that the 
performance of a FULL SIZE  2L Yagi can equal or 
surpass a heavily compromised multiband multi-element 
(trapped) tribander.

There is another hidden compromise in most 3L tribanders.
Typically, the higher the gain, the lower the feed impedance
for 3L Yagi's.  If a matching system is not employed the
antenna must be de-tuned to raise the feed impedance to
50 ohms, resulting in LESS  GAIN when split dipole feeds
are used. Wide spaced (>.15WL) 2L Yagi's inherently have 
higher feed impedances and therefore are less compromised 
when tuned for 50 ohms.

Reflectors do not suffer the same destructive interference
as directors when lined up by band since the first element
seen by 10M energy is the 10M reflector.  On 15M, the
short 10M reflector is nearly transparent and the next element
seen is the designated 15M reflector.  Similarly on 20M, the
short 10 and 15M reflectors are nearly transparent and the
next element seen is the 20M reflector.

(I'm sure there are exceptions and that I will get hammered
on these GENERALIZATIONS, but for the most part I believe
these statements to be valid.)

de  Tom  N4KG

On Tue, 3 Apr 2001 writes:
> The C3S has a split 20M driven element with closely coupled
> 15 and 10M elements.  There is a single 10M director and
> single 15 and 20 M reflectors.  The C3E has a 10M reflector,
> making 3 elements on 10M.  The 10M director is virtually
> 'invisible' on the lower frequencies.  There are NO directors
> for 15 or 20M because that would create destructive interference
> in front of the array on 10M (and 15).  REFLECTORS can be
> lined up in band order but DIRECTORS cannot.
> de Tom  N4KG
> On Wed, 04 Apr 2001 03:12:13 -0700 Tom Osborne 
> <>
> writes:
> > 
> > Hi Gang
> > 
> > In looking at a C3S in a picture, I was wondering, it it 3 driven
> > elements with directors or reflectors?  73
> > Tom W7WHY
> > 

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