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@w8ji.com>
Sent: Monday, February 16, 2015 9:40 PM
To: "Kees Nijdam" <clnijdam@knid.nl>; <topband@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
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|