Hi Guys,
Recently i inquired about opinion on Force 12 yagis and Tennadyne
T-6's. i see it stired some controversy and i'm not adverse to
controversy if it serves a useful purpose. This "list"(towertalk) serves
a useful purpose and i think its to our advantage to hear all sides of a
story, in our quest for knowledge. Besides ,i love a good controversy
when it involves a subject that i'm interested in, like antennas. Let the
controversy rage! :o)
I'm in agreement with the person who wrote that you choose log
periodics for wide bandwidth, yagis for "gain." All antennas cannot
compete "heads up." Each has a blend of characteristics that make it what
it is and that recommends when, where, and who will use it. The military
,embassy's,etc. have long favored the log periodic. It needs no defense.
Think about the fact that a 1/4 wave vertical has a theoretical gain of
1.2 dbi, or thereabouts. A dipole has a gain of about 2.1 dbi. According
to a recent post on TT, the Mosley TA-33M, in one particular test, had
1-2.7 dbd of gain,depending on the band. Thats probably rather typical of
the "trapped" tribander. Next up the gain "foodchain" comes the 2 element
yagi with probably about 4-4.5 dbd of gain, the 2 element quad with
5-5.25 dbd, the 3 element yagi @ about 6dbd, etc. Get the picture?
Propagation being the "great leveler" of signals, continuously in a
state of flux, smiles first on your qth, then mine. First on your
antenna, then mine. Theres really a rather small difference in gain
between these antennas, when it comes to using them to make contacts on
the air, especially when comparing the ones close together in the
"foodchain." Thats why its so difficult to authoritatively and
definitively state that one antenna or another is better, when it comes
to gain claims.
Before you claim that your antenna is great and mine is junk, you must
define exactly what criterion you are using to make that judgement. I
personally am a bit more concerned with gain. BUT, not just gain, good
front to back and front to side ratio, and a manageable size, and good
SWR.
After considering both the Force 12 products and the Tennadyne T-6, i'm
inclined to go with the Force 12 C3SS. To me that represents the best
compromise of characteristics that i'm looking for in a yagi. But the
Tennadyne T-6 has a lot going for it too! I do remain skeptical about the
gain claim of 5.1 dbd. But tonight i am reminded that ,since no one has
"defined" dbd as it relates to the Tennadyne T-6(and Tennadyne products
in general), i can't be sure that the reference standard isn't a dipole
in free space as opposed to a dipole at a given height above ground in
the "real world." My own thinking on that subject leads me to believe
that its gain probably is more like 3-3.5 dbd of gain, with the "real
world" dipole as the standard. What do i base this on? Read on.
The yagi depends on a driven element with parasitics nearby, one or
more, tuned quite closely to the driven elements freq. The reflector is
tuned about 5% lower, the director about 5% higher. At the risk of
oversimplification, the log periodic covers perhaps an octave to an
octave and a half in freq. The T-6 covers 13-30 mhz., or thereabouts. 6
elements in a 17 mhz. bandwidth, must be spaced in freq. about 2.8 mhz.
from each other. It appears impossible to have any 2 elements in such
proximity to each other so as to compliment each others tuning the way a
2 element yagi does. Therefore i find it impossible to believe that the 6
element 17 mhz. bandwidth T-6 can have more gain than a 2 element yagi.
Yet clearly the elements in the T-6 must have some complimentary effect.
This inability of users to directly compare the gain claims of
manufacturers products will remain such, till the day comes that we
demand the manufacturers rate their products in such a manner that
honest, well defined standards are used to compare their claims. Till
then, we'll have to discuss it(cuss it) ,make our choices and pay our
money, and take our chances. Personally, i'm not in competition with
anyone else, so if your antenna beats mine, oh well. Your power level is
likely to beat mine too, since i'm primarily a QRP'er. I've done the KW
thing! :o)
There are reasons why one might prefer a log periodic. Some of them
have double boom construction. That is conducive to strength. Wide
bandwidth, lower SWR over that bandwidth. Even if the T-6 has only 3-3.5
dbd of gain, thats not necessarily bad. 1-2 dbd down from a C3SS or C3
or C3S is probably relatively insignificant. If i had one or the other, i
doubt that it would stop me from making a contact in a given instance.
The T-6 is readily available, right off the shelf, shipping prepaid in
CONUS. Thats a rather significant benefit. The Force 12 antennas are not!
2-3-4 weeks delivery time.
I still find myself thinking about cutting and running and ordering a
T-6. After very patiently waiting for several months to complete several
aspects of my tower project, and being held up for weeks lately by
Hurricanes Dennis and Floyd, i'm beginning to feel a little impatient. I
wish i could find a C3SS on the shelf, or even a C3S, or a C4S.
73 all, Roy Lincoln WA4DOU Elm City, N.C.
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