The objections you voice are precisely the reasons behind the Force 12
C3 & C3S and antennas of similar design.
Traps will always narrow bandwidth. Shorter booms will always have
narrower bandwidth than longer booms, all other factors held constant,
due to the greater mutual coupling of the elements. Greater bandwidth
will result in lesser gain, all other factors held constant. All these
factors become compromise settings in *any* yagi design.
Our obvious more-gain-is-always-better-no-matter-what mentality is
easily perceived by antenna makers who shade their design for best
gain, and at the expense of guess what... If they don't, they loose
sales, even if they know, and some of us know, that bandwidth or F/B
may make far more difference during day-in and day-out operations.
Personally, I would give up a half db gain for 5 db f/b. I gave up on
ultimate bandwidth on 15 meters after several hundred hours monkeying
with yagi designs in modeling programs. Have to give away *too much*
to get all 450 under 1.5 swr.
Running barefoot I turn on the Auto antenna tuner in the FT1000MP.
Running power with the AL1200, I splat the bandwidth vswr with 1200
watts of plate dissipation, and don't care. *NOTHING* I can do in the
shack or the feedline, or any place except the antenna design, can
help the F/B & F/S that make such a big difference in hearing the weak
ones.
I used a TH3 for many years. I finally gave it to PEARL (Putnam
Emergency & Amateur Repeater League, Putnam County, NY) for a field
day antenna when I moved south to NC. If that had been a C3 or C3S, I
would have kept it.
I currently have a C31XR, which is a cannon, receiving and
transmitting. It hears weak ones better, partly because of a somewhat
better gain, but more because F/B and F/S are so deep that the ambient
noise drops 5-10 db, depending on direction. Signals in the gain lobe
are louder, *and* the background noise (that goes away when I switch
the antenna to ground) is less than other antenna's (e.g. 20 m dipole
broadside same direction as yagi).
But this is one of the "bigger...not an option" jobs, as would be the
C3, Bencher Skyhawk, etc?
If I had to do things with minimum size/weight I would probably get a
C3S (12' boom, 26#, 18.9 Turning radius). If turning radius was a
problem, then the C3SS - same with linear loaded 20 elements. (12 foot
boom, 27#, 13.6 Turning radius). Interesting enough, the C3SS has a
better published F/B on 20 than the C3S with only slightly reduced
gain (-0.4db) on 20m.
Another factor that bears in is the feedline loss. If a certain length
is dictated by station particulars, and the RG8/RG213 type is dictated
by budget constraints, the swr will be lowered by coaxial necessity,
possibly widening published bandwidth specs to seemingly acceptable
levels. Note however, that loss in the coax is substituted for lowered
xcvr output levels. No real change.
In a contest with both CW and Phone contacts, if the antennas are
tuned for CW and using the tuner for SSB, tuner in/out does the trick.
Or maybe the other way around. The C3 & other antennas can be set for
compromise or specific settings. I would be tempted to ignore the
compromise settings and use a tuner for the least used mode. In my
case cut for CW and tune for SSB. I would particulary do this if the
F/B chart for the antenna shows a narrow max (most do). Set the F/B
for the most used *receive* frequency and let the rest fall where it
may.
You sure you couldn't get up a C3? (18' boom, 32# & 19.8 turning
radius)
73 & Best 'o luck.
Guy
On Mon, 18 Jan 1999 17:49:29 -0800, Tom Osborne <w7why@harborside.com>
wrote:
>
>
>Hi All
>
>After this weekends NAQP, I've just about come to the conclusion
>that 2 el monobanders would be better than the TH-3 I'm currently
>using.
>Right now, the TH-3 is cut for the CW band, and as many who own
>the TH-3 know, the bandwidth is not all that great. I had to run
>it through the tuner all weekend on all three bands. I'm sure
>gain is gone having to use it this way. I think that some
>wide-band 2 el monobanders for 10-15-20 would work better than
>trying to run an antenna with a SWR of 4 to 1 on one end of the
>band or the other. I had a 15 meter 2 el wide spaced monobander
>up before the TH-3, and it was good from 21.000 up to about
>21.300 before the power would start dropping off. I'm really
>starting to think I made a mistake taking it down, but I thought
>the convenience of a tri-bander would offset the difference in
>efficiency of the mono/tri-bander. The problem is I've got one
>SMALL tower, and no room for another one and I wanted something
>for 10 meters, too. Oh well, I guess we really can't have our
>cake and eat it too. A bigger tri-bander is not an option at
>this time. 73
>Tom W7WHY
Guy L. Olinger
k2av@qsl.net
Apex, NC, USA
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