follows the presentation of the Roomcap Antenna with the help of an
This shows the unique properties of this antenna very impressively.
Nearly no other antenna offers such good values without the use of an
All the following measurements are made with the 20m antenna without
top capacity, installed on the car
and measured at the feed point through 1 m coax cable of 50 ohms.
In this graph you see the SWR (in blue) and the serial resistance Rs
(in red) of the antenna in function of the frequency.
The scale of the red curve is onthe left border, and the scale
of the blue curve is on the right border.
You see, that the SWR 1:1 is reached just above 14 MHz, and that
the bandwidth (for SWR 2:1) is 260 KHz.
The markers M1 and M2 indicate the frequencies for SWR = 2:1.
The course of Rs shows at resonance 50 ohm, and therefore the ideal
match of the antenna.
The Smith-Chart has in the center of the green circle 50 ohms, and
therefore the point for SWR 1:1. The green circle represents
the curve for SWR= 2:1. The blue point corresponds to M1 at 13.9 MHz
with Rs 24.8 ohm, and the red point M2 at 14.162 MHz
and Rs 63.2 ohm. Between these two points the SWR is below 2:1, and at
the center 1:1.
The Smith-Chart is explained here: http://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf
Here you see in red the phase curve, and in blue the course of the
reactive component Xs of the antenna.
You note the resonance by the large phase jump, while at the same time
the reactive part Xs reaches a minimum (nearly zero).
The marker M1 shows the resonant frequency (14.028 MHz).
In the Smith-Chart you recognize, that at resonance the center of the
circle is reached with SWR 1:1 (1.028), while
the impedance Z of the antenna is practically 50 ohm (49.742).
Here you see in red the reflected power in percent, and in blue the
course of the antenna impedance Z.
It shows at resonance zero reflected power, and 11 percent reflected
power at SWR 2:1.
Here, you see that at resonance (marker M1), the impedance Z is
just reaching 50 ohms.
Please remember, that the resonant frequency of this antenna is set in
seconds to any frequency of the band, just by using
the RFA (Remote Frequency Adjustment). Therefore, you obtain ideal
conditions on each frequency of the band!
This explains the good operational results of this antenna.
All without using variable capacitors or sliding coil taps ... this is
result of the unique Varylink-System.