Topband: Strange behaviour of radial systems

[Kees Nijdam]

Tom,

Thanks for your reaction.
At 50m distance of both verticals I have a 16m high tower with a 3 el 
Steppir. This tower has a radial system and is shunt-fed tuned for 80m. 
There is some interaction with the 2 element system on 80m. 400 Watt in this 
system generates less than 1 Watt in the shunt-fed tower.
Along this tower runs also my 160m inverted L, 16m vertical and 30m 
horizontal, with a 20 m long rope connected to vertical nr 1 of the 2 
elements system, at a hight of 17 meters. The distance of the end of the L 
to vertical nr 2 is a about 15 meter.
During the measurements I disconnect the inverted L antenna from the coax. 
It is floating.  Furthermore there is a 100 m long beverage , 1 meter high 
running at 10 meter distance from vertical nr 1, 20 meter from vertical nr. 
2.

Earth conductivity measurements on 1,8; 3,5; 7; 10,1 MHz. With 2 conductors 
50 cm into the ground.
Vertical nr 2 little better conductivity for 1,8 and 3,5 MHz.

Both verticals of the 2 elements 80m system are almost the same.  35,5 - j23 
Ohms on 3520 kHz and 41+/- j0 Ohms at resonace=3670 kHz.
But on 1825 kHz is a big difference.... Why?
I am curious to know.

Kees, PE5T

--------------------------------------------------
From: "Tom W8JI" <w8ji at w8ji.com>
Sent: Monday, February 16, 2015 9:40 PM
To: "Kees Nijdam" <clnijdam at knid.nl>; <topband at contesting.com>
Subject: Re: Topband: Strange behaviour of radial systems

> Kees,
>
> What else is around your verticals? Just the fact something is not 
> resonant does not mean it isn't a problem.
>
>> To my ashtonishment, vertical 1: 28-j328 Ohm and vertical 2: 12-j320 Ohm 
>> both on 1825 kHz.
>> The vertical with the smallest radial system has the lowest earth 
>> resistance (around 5 Ohms, estimating 7 Ohms radiation resistance for a 
>> 21m high vertical).
>> The oldest vertical (nr1) with 50 radials seems to have more than 20 
>> Ohms.....
>>
>
> Since it is a system with standing waves, even on the radials, impedance 
> at the base might not represent true ohmic losses.
>
>> I measured the earth conductivity with the 2-conductor method and I found 
>> that the soil under vertical nr 2 has better conductivity (maximum found: 
>> 25 mS/m) compared to vertical nr
>> 1 (maximum: 21,5 mS/m).
>
> If that is a low frequency measurement, I have never seen a measurement 
> like that mean very much on HF or higher. Typically you are measuring rod 
> contact and 50/60 Hz more than RF behavior.
>
> If it is an RF measurement, like rod centered on a large screen and 
> measured against the screen, it is much more useful but still not always 
> accurate.
>
> I have little faith in two rods, and no faith in something done on power 
> line frequencies.
>
> What you measure might not mean anything for performance.
>
> 73 Tom
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