Hi Pete, you wrote, in part:
>Hi Jim -- I'm really surprised at your SWR results, especially on 10
>meters! Makes me think my feeder must have a lot more loss than I'd
>thought.
Well, I think what I measured is not that different from the vswr numbers
published by Ward, N0AX and Steve, K7LXC in their test report
book about tribander performance. Will list their numbers and mine
at their test frequencies:
Frequency..........Theirs..........My C4
14025................1.5.................1.3:1
14100................1.4.................1.1
14175................1.4.................1.1
14250................1.6.................1.2
14325................1.7.................1..3
21025................1.2.................2.0
21125................1.5.................1.4
21225................2.1.................1.4
21325................2.7.................1.8
21425................3.5.................2.6
28050................2.0................2.8
28250................1.8................1.8
28450................1.8................1.3
28650................1.9................1.5
28850................2.2................1.9
For some reason, my C4 basic C3 section seems to
show somewhat lower vswr's across 20 meters than
the unit tested and reported on by Ward/Steve last May
at Dayton, and the data subsequently published in their
report. Maybe Tom changed something, hi?
Now on both 15 and 10 meters, it is clear that I mistakenly
used the nominal settings for the tip elements; thus I have
better swr in the phone area than in the CW bands. But,
as I am only a very casual contestor, I can take time to
fiddle with the antenna tuner to compensate and keep the
rig/linear happy with the situation. I gave my C4's resonant
frequencies in yesterday's post.
I have been asked about swr across the band for the C4 40 meter
element, the Force 12 EF-140S single linear loaded dipole; which
is 56% full length per Tom's instruction manual. Numbers:
7000........1.2:1
7025........1.4
7050........1.7
7075........2.2
7100........2.8
7200........4.7 (R=12, X=29)
7300........5.7 (R=8, X=12)
This antenna shows "resonance", that is X=0, between 7013
and 7032 as set up and measured with the MFJ-259B.
The feedpoint resistance increases from about 65 ohms at
7012 or so, to 80 ohms at 7033, so vswr never drops to 1:1
even though X=0 across this span.
I was deliberate in selecting the CW band segment for
opt performance; for 40 SSB, we use 7075 to 7100
most often in KH6 land. Just about never, when the band
is open, can we operate above 7100 because of powerful
broadcast, AM and SSB, signals from on West of us.
Had one request for a measurement of this antenna on 30 meters,
I guess to see how hard it would be for a tuner to match; here
are some numbers,
10105.......R=372 ohms, X=249 ohms(inductive since the dipole
is too long for 30 meters), and the vswr here is 9:1.
The auto tuner in my FT-1000D was able to tune all this out,
and put out a true185 watts CW into this Force 12 40 meter
dipole at 10105. Only signal I can find on 30 just now is some RTTY
stuff up at about 10130, 2328Z, BTW, at this power output,
the P3000 indicator shows a vswr on the feed to the EF140S
of 8:1, bit lower than that indicated by the 259B, but maybe
neither is too accurate at such high reflection, don't know.
In any case, probably would NOT be a good idea to use
a linear to boost the power up at such a high reflection
in the line. Line power handling goes way down with
the boosted peak voltage caused by the swr.
I certainly recommend that anyone contemplating the
purchase of a Force 12 antenna also buy Tom's
book, "Array of Light", sold by Force 12. Has a lot
of neat tidbits, and very useful info on putting up
yagis should you have yet not done this up on a tower, hi.
Hope this info helps to evaluate your own C4 set ups, and to satisfy
the curiosity of you others, hi.
73, Jim, KH7M
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