[TowerTalk] HyGain TH-2 problem

[Missouri Guy]

Roger,
 
The traps on my Hy-gain antennas are "sorta molded"...
they use a threaded plastic form for the coil, then the
outer metal sleeve becomes the "capacitor" which is 
connected to one end of the coil.  That forms the parallel 
tuned circuit, which is often tuned below a particular band
to avoid very high voltages at the operating frequency.
  
Resonance is achieved by using a length of tubing 
that is different from what would be used if the trap was 
tuned to the operating frequency.
 
Hope that helps...
Charlie, N0TT
 
On Mon, 27 Aug 2012 03:47:58 -0400 K8RI <K8RI-on-TowerTalk at tm.net>
writes:
> On 8/26/2012 9:00 PM, n8de at thepoint.net wrote:
> > Sounds like one or more of the 15m traps is defective.  Insects, 
> etc.,
> > can cause those problems.
> 
> Doesn't the Hy-gain tribanders use molded traps, or was that just on 
> the 
> older antennas?
> 
> 73
> 
> Roger (K8RI)
> 
> >
> > 73
> > Don
> > N8DE
> >
> >
> > Quoting Brian Alsop <alsopb at nc.rr.com>:
> >
> >> You would think this simple antenna should give one no problems.
> >>
> >> Wrong.
> >>
> >> Maybe some expert here can help solve this problem.
> >>
> >> Unfortunately I can mount it only up 22' on a chimney mount.  
> Currently
> >> fed with 61' RG8X and a 6 turn 6" diameter RG213 choke at where 
> the
> >> feedpoint spreads in Y fashion to the element halves.
> >>
> >> It works with one problem.   The 15M SWR is 2.7 at the low end of 
> the CW
> >> band.  The settings were made for CW.  The resonant point in the 
> HyGain
> >> manual for this "CW" setting is 21.175 MHz.  That's what I see. 
> The
> >> curve has not got the Hygain bandwidth.  The lower frequency 
> slope is
> >> quite a a bit larger.  The above resonance slope doesn't depart 
> too much
> >> from HyGain's.  This larger slope is what is causing the high SWR 
> at the
> >> low end of the CW band.
> >>
> >> I'm using the K3 SWR readings.  They are not that different from 
> what an
> >> AUTEK RF-1 gives.
> >>
> >> The elements are like this:
> >>
> >> --------Y-----T10---X---T15-----Z----   Half driven element.
> >>
> >> Where X,Y,Z are dimensions.
> >> T10 is the 10M trap
> >> T15 is the 15M trap.
> >>
> >> I wanted to try and move the resonance on 15M down the band about 
> 85 KHz
> >> to bring the CW SWR under 2:1. I determined that that meant 
> lengthening
> >> X by 3/8" on the driven element half and 0.5" on the reflector 
> half
> >> element.  This was determined by extrapolation of the slopes of 
> the
> >> length curves given in the manual.
> >>
>  "This height at 15M is 1/2 wavelength so it should be high enough 
> to
> >> avoid too close to ground effects.  Obviously it is about 6' 
> over
> >> standard shingled roof.
> >>
> >> It was expected that the bandwidth is less than the HyGain manual 
> gives
> >> for 70' up."
> >>
> >> I made these length changes and NOTHING changed.  The resonant 
> point was
> >> identical!
> >>
> >> I've ruled out backwards 10M traps and driven element 15M traps 
> are
> >> indeed on the DE.  20/10M are fine.  Turning the beam 90 degrees 
> doesn't
> >> change anything.
> >>
> >> So what magic dimension does one change to bring the resonant 
> frequency
> >> down on 15M?
> >>
> >> And why 15M and not the other two bands.
> >>
> >> "USE A TUNER" is not a solution.
> >>
> >> Brian/K3KO
> >>
> >> (Previously had a TH-2 at 80' on a HAZER arrangement.  Tweaking 
> it was
> >> straightforward by numerous up/downs to 40')
> >>
> >>
> >> -----
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> 08/26/12
> >>
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