Varylink and Remote Frequency Adjustment
show two important functions of the Roomcap antenna:
The VARYLINK and the RFA (Remote Frequency Adjustment).
The following pictures are made from the 3 band antenna on 40m,
installed on the car.
is a function which allows the precise matching of the antenna to the
of the coax cable, that is, setting of the SWR. This permits to adapt
the antenna to the real
environment. That means, that the antenna does not need an antenna
tuner, but only needs a setting
at installation time, to obtain best SWR.
An antenna tuner adds losses, which are between 8 to 50%, depending on
the amount of
tunig required, while the feeding system with Varylink is working
Here, you see the red SWR curve (v form), which shows at resonance
(7.109 MHz) an SWR of 1.03.
The resonant frequency is indicated by the green dashed vertical line.
On the left border of the graph is the scale of SWR, from 1 to 10,
and at the the right border the
scale of Z, from 0 to 500 ohms. The values at resonance are in
the line "Min. SWR".
The antenna offers at resonance an impedance Z of 51.03 ohms. The real
component of Z is 51.02 ohms (R)
and the reactive part is 1.04 ohms (Xs). R.L. is the Return Loss
At resonance the broad, black curve Z touches the red dashed 50
By moving the Varylink, you move this broad Z curve up or down.
By moving the
Varylink, the Z curve is
moved upwards to 99.65 ohms, which corresponds to
an SWR of 2. You note clearly the moved Z curve.
In this example,
the Z curve is moved downwards, resulting in an impedance of 25 ohms,
corresponds again to an SWR of 2.
(Moving the Varylink mechanically upwards, the Z curve is moved
downwards, and reverse.)
Adjustment) permits remote setting of the resonant
of the antenna. At the installation of the antenna, the
Varylink ist set to the
lowest SWR, as has been shown above. This setting remains unchanged
when changing the frequeny.
The actual operating frequency is the set by the RFA within seconds by
means of a small electro
motor inside of the Varylink. This allows setting to the lowest SWR for
any frequency in the band
Here, the antenna is set to 7.050 MHz. If you want to change to the
band end, you
press shortly the button "up" of the RFA control box, and you obtain:
Here, the resonant frequency is on 7.191 MHz, keeping the same SWR as
The RFA is moving both curves sideways, to the
left or to the right.
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