[TowerTalk] 160M Antenna puzzlement

[Richard (Rick) Karlquist]

What I do is use an autotransformer at my antenna to transform
the ~25 ohm resistance at resonance to ~50 ohms.  This
basically takes the feedline out of play.

Rick N6RK

On 12/19/2021 7:59 AM, Pete Smith N4ZR 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).
>