Quick Installation Guide
Document
WERA4-Quick-US-200917
Page 35 of 73
The antennas should be tuned to the intended working frequency and it needs to be
matched to 50
, low VSWR over a wide bandwidth > 500 kHz.
Please note,
always use a cable of at least ¼ wave length to connect the antenna meter.
Layout this test cable almost identical to the proposed layout for the final connection,
otherwise the readings will be incorrect.
As test cable the longer one of the phase cables for the Tx array can be used. Nobody
should be standing next to the antenna and metal material (ladder, tool box) should be
removed from the antenna.
If the antenna’s bandwidth is wide like it is shown in the graph on the left picture, then tune
the antennas centre frequency to working frequency.
If the antenna’s bandwidth is more narrow like on the right picture, then tune the antenna a
little bit to the left or to the right of the working frequency. Choose that side, where the
graph has a smooth shoulder and use
this side for all antennas
.
Please note
, metal fences, power cables or other electrically conductive material should
be avoided within 1 electromagnetic wavelengths distance around the antennas.
Particularly the Tx array is sensitive to metal constructions close to it.
The resonance can be tuned by changing the length of the antenna pole. A variation of
about 20 cm can be achieved by changing the antenna tuning coil connection to the pole.
If this fine tuning (+/-150 kHz) is not sufficient, there are additional options for tuning:
-
If the antenna tuning coils are new, they may not be sealed. In this case the frequency
can be shifted lower by pressing the winding of the coil closer to each other and vice
versa.
-
The mounting height above ground level will influence the position of the resonance
frequency. A higher elevation will typically increase the frequency.
-
The radial length will have a strong effect on the frequency. Shorter radials will
increase the resonance frequency.
-
The layout of the radials will have an influence as well. Keeping the radials higher
above ground will increase the frequency and laying it on the ground or even
connecting the end to the ground will decrease the resonance.
Regarding the matching (VSWR) the last three modifications will strongly chance this
parameter as well. The VSWR is more critical for the Tx array. It should be better than 1:2
at centre frequency with a tolerance of +/- 0.3 for all antennas.
For the Rx array the VSWR should be better than 1:2.5 at centre frequency with a variation
of +/- 0.4 for the whole array.
Please note, that the VSWR values given above, are the values at the centre frequency,
not at the resonance. The values at the resonance are typically much lower.
It is recommended to note the antenna parameters of each antenna in the log book:
- Resonance, VSWR at resonance, Band width for VSWR 1:2, VSWR at centre frequency
5.6.2 Tx-Antenna Tuning