[TowerTalk] HyGain TH-2 problem

[K8RI]

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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