Base Station Grounding - Vertex Standard VX-1700 Operating Manual

I
NSTALLATION
Excellent reference texts and computer software are avail-
able for the design and optimization of HF antennas. Your
dealer or installer should be able to assist you with all as-
pects of your antenna installation.
Use high-quality coaxial cable for the lead-in to your VX-
1700 transceiver. All efforts at providing an efficient an-
tenna system will be wasted if poor quality, lossy coaxial
cable is used. Losses in coaxial lines increase as the fre-
quency increases, so a coaxial line with 0.5 dB of loss at 6
MHz may have 2 dB of loss at 26 MHz (1 dB is a just-
perceptible decrease in signal strength). As a general rule,
smaller-diameter coaxial cables tend to have higher losses
than larger-diameter cables, although the precise differ-
ences depend critically on the cable construction, materi-
als, and the quality of the connectors used on the cable.
See the cable manufacturers' specifications for details.
For reference, the chart below shows approximate loss fig-
ures for typically-available coaxial cables frequently used
in HF installations.
Loss in dB per 30 m (100 ft)
For Selected 50 Ohms Coaxial Cables
(Assumes 50 Ohms Input/Output Terminations)
C T
2 MHz
RG-58A 0.55
RG-58 Form 0.54
RG-8X 0.39
RG-8A, RG-213 0.27
RG-8 Form 0.22
®
Belden 9923 0.18
RG-17A 0.08
Loss figures are approximate; consult cable manufac-
tures' catalog for complete specifications.
Loss figures can increase significantly if high SWR is
present on the transmission line.
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B S
ASE TATION
L
15 MHz 28 MHz
1.75 2.60
1.50 2.00
1.07 1.85
0.85 1.25
0.65 0.88
0.50 0.69
0.30 0.46
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NSTALLATION

Base Station Grounding

The VX-1700 HF transceiver, like any other HF commu-
nications apparatus, requires an effective ground system
for maximum electrical safety and best communications
effectiveness. A good ground system can contribute to sta-
tion efficiency in a number of ways.
It can minimize the possibility of electrical shock to
the operator.
It can minimize RF currents flowing on the shield of
the coaxial cable and the chassis of the transceiver
which may cause interference to nearby home enter-
tainment devices or laboratory test equipment.
It can minimize the possibility of erratic transceiver
operation caused by RF feedback or improper current
flow through logic devices.
An effective earth ground system may take several forms;
for a more complete discussion, see an appropriate RF
engineering text. The information presented below is in-
tended only as a guideline.
Typically, the ground connection consists of one or more
2.4m (8') copper-clad steel rods, driven into the ground.
If multiple ground rods are used, they should be config-
ured in a "V" configuration, and bonded together at the
apex of the V which is nearest the station location. Use a
heavy, braided cable (such as the discarded shield from
type RG-213 coaxial cable) and strong cable clamps to
secure the braided cables to the ground rods. Be sure to
weatherproof the connections to ensure many years of re-
liable service. Use the same type of heavy, braided cable
for the connections to the station ground bus (described
below).
Inside the station, a common ground bus consisting of a
solid copper pipe of at least 25mm (1") diameter should be
used. Another ideal ground bus may consist of a wide cop-
per plate (single-sided circuit board material is ideal) se-
cured to the bottom of the operating desk. Grounding con-
nections from individual devices such as transceivers, power
supplies, and data communications devices should be made
directly to the ground bus using a heavy, braided cable.
Do not make ground connections from one electrical de-
vice to another, and thence to the ground bus. This so-
called "Daisy Chain" grounding technique may nullify any
attempt at effective radio frequency grounding. See the
drawings below for examples of proper and improper
ground connections.
Inspect the ground system - inside the station as well as
outside - on a regular basis so as to ensure maximum per-
formance and safety.
Transceiver Linear Power
Amplifier Supply
P G C
VX-1700 O
Transceiver Linear Power
Amplifier Supply
"Daisy Chain"
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M