The ground (earth) system is a key part of the overall antenna system and consequently the
system operation. An inadequate ground system is the primary cause of poor performance
and tuning problems. There is little point in installing the antenna unless a good ground
system can be provided. In areas of good ground conductivity (ie. ground always damp), an
effective ground can be made through a grounding rod. This should be approx. 3 metres in
length and should be installed as close to the tuner as possible. Several rods bonded
together will improve the ground contact. In some cases metal water pipes may be used as
a ground providing:-
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The water pipe is close to the tuner and the water pipe enters the ground close to
the tuner.
There are no joints or couplings in the pipe that will increase the resistance path
to ground.
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The water pipe enters soil with good conductivity.
A low resistance joint is made with the water pipe.
Frequently the ground conductivity will not be sufficient to provide a satisfactory ground for
the Barrett 911 tuner. This will almost certainly be the case in well drained sandy soils or on
rock. In these cases a counterpoise must be used as a ground system. This will also be
the case in rooftop installations where no existing ground plate (such as metal roofing
exists). A counterpoise can consist of radial wires or a mesh made of materials such as
chicken wire. If radial wires are used the counterpoise should consist of at least 8 to 10
radial wires, each radial being at least 5 metres in length. When radials or mesh are used at
ground level it is recommended that they be buried a few centimetres below the surface.
After mechanical installation is complete select the highest frequency to be used on the
transceiver. A directional watt-meter such as a bird model 43 should be inserted in the
coaxial transmission line between the transceiver and the tuner. The tune mode on the
transceiver is then energised (refer to the transceiver user manual). Upon application of RF
energy, the tuner should start to tune, indicated by the 'clattering' of the tuner relays. After a
few seconds the relay noise will cease, the transceiver should indicate a successful tune
and the watt-meter reflected power should indicate a low value consistent with a VSWR of
better than 2:1. Now select the lowest desired frequency on the transceiver and repeat the
above procedure. The result should be the same, except that the tune cycle may take
somewhat longer. If the above procedure does not give the results as indicated check that
the antenna length and connections are correct and re-check all ground (earth) connections.
Ground (earth) system
Electrical checkout
Note:-
When received, the Barrett 911 automatic antenna tuner memory system will
usually not have any pre-stored tuning information appropriate to your
installation. To allow the 911 to 'learn' its tuning information simply proceed
from one channel to the next allowing the normal tune cycle to take place.
Each successful tune is 'memorised' so that when that channel is re-
selected the tuner will almost instantaneously retune to that frequency.
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BARRETT 950 HF TRANSCEIVER
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