Demonstration of:                                
Varylink and Remote Frequency Adjustment                             

                                                                   5th.January 2011                                                                                                                                                                        

Here, I would like to 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.

The Varylink is a function which allows the precise matching of the antenna to the impedance
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 practically lossless!


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 in dB.
At resonance the broad, black curve Z  touches the red dashed 50 ohm line.
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, which
corresponds again to an SWR of 2.
(Moving the Varylink mechanically upwards, the Z curve is moved downwards, and reverse.)

The RFA (Remote Frequency Adjustment) permits remote setting of the resonant frequency
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
within seconds.

Here, the antenna is set to 7.050 MHz. If you want to change to the higher 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 before.
The RFA is moving both curves sideways, to the left or to the right.


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