[TowerTalk] 160M Antenna puzzlement

[Pete Smith N4ZR]

I hope that's not the case, Mike.  There is already a two-toroid common 
mode choke between the coax and the antenna, wound with RG-400.

73, Pete N4ZR
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On 12/19/2021 11:30 AM, Mike Fahmie via TowerTalk wrote:
>   I'm guessing that the coax run is acting as another radial in your ground system. You can test this theory by placing a ferrite or isolator at the antenna end of the coax run.-Mike-WA6ZTY
>
>      On Sunday, December 19, 2021, 07:59:34 AM PST, Pete Smith N4ZR<pete.n4zr at gmail.com>  wrote:
>   
>   I may be suffering from a case of too much information, but I'm puzzled
> by my new 160-meter inverted L, about 60 feet vertical with 8 on the
> ground radials each about 65 feet long
>
> My old inverted L broke, so I put up a new one recently.  To my
> surprise, it resonated well above the band, indicating it was about 12
> feet short.  Because of uncertainty about the availability of additional
> height at the top corner,  I temporarily added the additional length at
> the bottom and loosely coiled it.
>
> Measuring the SWR and R/X at the base of the antenna with my Rig Experts
> AA-55 Zoom, I now see a nice textbook SWR curve centering on 1820 KHz.
> Measuring the R and X at the same place, I see R of about 30 ohms and X
> crossing zero near the same frequency.  That seems a little low for only
> 8 radials on the ground but...
>
> So now I come into the house.  The feedline is about 75 feet of RG-8X to
> my tower-mounted antenna switch, and then about 170 feet of Buryflex to
> the shack.  I'm well aware (in general arm-waving terms) of the
> impedance transformation effect of feedlines, and even at 160 this one
> is fairly long, but:
>
> In the shack, I see the same nice SWR curve, centered about 10 KHz
> lower. The confusion arises with the R and X curves - the R at resonance
> is a little lower - about 26 ohms - but rises on the upside to about 140
> ohms at the high end (around 1920 KHz and then drops steeply to around
> 12 ohms by 2150 KHz.  The X value, on the other hand, crosses zero at
> around 1780 KHz, and rises to around 70 ohms at 1870 KHz and then dips
> sharply, crossing zero again at 1915 KHz.
>
> So, two questions:
>
> 1.  Is what I am seeing simply the result of the feedline transformation
> of R and X, and
>
> 2.  If it proves impossible to raise the knee of the inverted L further,
> can I just leave that small coil of wire in place at the bottom of the
> inverted L?  It seems to work pretty well  - I worked a number of
> Europeans last night in the Stew, although it was tough to hear them (I
> have not yet reinstalled my K9AY loop).
>