3. The water pipe enters soil with good conductivity.
4. 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. When radials or mesh
are used at ground level it is recommended that they be buried a few centimetres
below the surface.
fter mechanical installation is complete select the highest frequency to be used on
the transceiver. A directional wattmeter 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 wattmeter reflected power
should indicate a low value consistent with a VSWR of better than 2:1. If the cover
of the tuner is removed the PCB mounted 'TUNED' LED should be illuminated.
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.
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.
MARINE INSTALLATIONS
Antenna
Transceiver and Tuner Mounting
Ground (Earth) System
On sailing vessels the antenna can either be an insulated backstay or a whip
antenna mounted vertically, usually on the stern. Best performance will be
achieved by using an insulated backstay as the radiating length will be longer than
that available when using a whip. The top insulator on the backstay should be
approximately 300mm from the mast and the bottom insulator should be at eye
level above the deck. The distance between insulators should be greater than 10
metres and less than 35 metres. A whip antenna is generally used on small to
medium sized power vessels. There are different length whips to suit the vessel
length.
Select a suitable position in the vessel to mount the transceiver. It should be a
position that is out of the weather and easily accessible to the operator, whilst as
close as practical to the 13.8V DC power source. Mount the transceiver to a solid
fixing point using the mounting cradle. Make sure there is sufficient space at the
rear of the transceiver to connect the power and antenna cables.
The antenna tuner should be mounted as close to the antenna feed point as
possible. In metal vessels the length of the feeder from the antenna tuner to the
feed-through insulator, inside the vessel, should be kept less than 1 metre.
The antenna feed cable should be a suitable high voltage cable. Care should be
taken to avoid sharp points when terminating the cable to prevent corona
discharges.
The interconnect cable supplied with the antenna tuner should be routed away from
other cables back to the transceiver and connected as indicated in the diagram
overleaf.
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.
Metal hulled vessels provide an almost perfect ground. The tuner ground terminal
should be connected directly to the hull using the shortest possible ground strap.
The point of connection to the hull should be prepared so that it is free of paint and
rust to ensure a good contact area with minimum electrical resistance.
Wooden or fibreglass vessels present more of a problem to ground. Ideally the
vessel should be fitted with an external copper ground sheet, connected to the
interior of the vessel by suitable stud or an earth plate ("E" plate Barrett P/N
BCA51700)
If the vessel is yet to be constructed, then in the case of fibreglass vessels a thin
copper sheet with an area of not less than 4 square metres should be moulded into
the hull during lamination. A suitable heavy strap should be connected to the sheet
and left free for earth connection.
