You will find that the tuning of a 40 meter dipole varies nearly as
wildly with such changes in height, it's not a Force 12 thing at all.
Further if the dipole is shortened by any of the various means, it
becomes MORE sensitive to heights </= a 1/2 wave, not less sensitive.
Again not a Force 12 thing, just physics.
The reason it's more obvious on 40 meters is that a halfwave is ~70
feet. The ground is in the NEAR field and able to influence an
element's self-resonance.
Personally, I think it's high time for resurrection of the grid-dip
meter, and setting a LL element's resonance BY ITSELF >>> !!! AT
HEIGHT !!! <<< to the factory specified resonance settings.
THEN assemble the thing.
The argument about that is that it's too much work. Folks would rather
take the short cut and just assemble and throw it up there.
Except the short cut almost always winds up being a LONG cut. If you
have to climb the tower and lower it to mess with it and put it back
up, you've already lost any advantage by throwing it together and
putting it up.
73
----- Original Message -----
From: "Gene S." <gene@aspen-ridge.net>
To: <Towertalk@contesting.com>
Sent: Sunday, August 18, 2002 4:37 PM
Subject: Fwd: [Towertalk] Force12 C4-SXL
> I installed a C4-XL a few weeks ago, same basic design as your
C4-SXL.
>
> Tuning the 40 meter elements is an interesting affair.
>
> With advice from Natan and Pete Smith N4ZR, I got the linear
loading
> assemblies constructed and put the antenna in the air. The
assembly
> manual needs a lot of help in the 40 meter section, to be blunt, it
> stinks. The C-3 manual is excellent.
>
> Make sure you have the linear loading wires in the correct
> configuration, the manual refers to as "staggered". Initially, I
didn't
> see what they meant by "staggered" and did it wrong.
>
> At my location I found the 40 meter portion of the antenna to be
"very"
> sensitive to the ground. Trying to tune it at 10 - 12 feet above the
ground
> was a waste of time.
>
> You didn't say if you found a dip in the SWR near any band segment
on
> 40. I found the specs given in the manual are approximations.
Setting
> them to the 7190 suggested point gave me a dip at 7.000 Mhz.
Trying to
> find the dip at 12 feet above the ground never resulted in anything
better
> than 3.0 to 1 that you're seeing, it had to go up higher.
>
> Natan suggested that I set the reflector and driver to the
measurements in
> the manual (as a starting point) and further adjust the driver only.
I did
> change the suggested reflector setting slightly, but made all
subsequent
> adjustments on the driver.
>
> At 25 feet the SWR was 2.0 to 1 at 7190. Raising the antenna to 75
feet
> dropped the SWR to 1.5 to 1.
>
> Finding the dip was important because it indicated the antenna did
load,
> but it was being affected by the ground. I made a few adjustments of
the
> tuning jumpers and the hairpin and got the SWR to 1.5 to 1 at 7190
when
> the antenna is at 75 feet, it does stay low across the suggested
130KC
> range. The hairpin is spread about 3/4" between the turns.
>
> SWR on the other bands is virtually flat, the front to back is
> excellent. The performance on 10 - 15 - 20 is noticeably better
than my
> 25 year old KT-34.
>
> It does work, but the manual is weak when addressing the linear
loading
> wires and their assembly. A couple of "good" pictures would have
saved me
> many hours of hunting an pecking..
>
> 73,
>
> Gene K5GS
>
>
> >I am having hard time to lower SWR on 40 mtr band on C4-SXL. I
have
> >just finished the assembly and found this problem. all ok on 10 -
20
> >meter band SWR.
> >I used RF choke ( 10 inch dia.) and connected hair-pin coil...SWR
shows
> >10.
> >I removed hair-pin coil....SWR shows 3.
> >I did spreading or pushing the coil, but it didn't change at all.
> >I rechecked LL assembly, but I couldn't find anything .
> >
> >I must have made some thing wrong, but I couldn't figure out.
> >
> >de VE3JOY, Isao Endo
> >
>
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