Grounding - RM Italy BLA600 User Manual

Solid state hf & 6m 500w linear power amplifier
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12. Grounding:

It is beyond the scope of this manual to provide a definitive guide into the
controversial subject of RF grounding, as it is a subject all to itself and very much
depends on how the equipment is connected and types of antenna used. There are
both arguments for and against the stereotypical RF station ground. An additional
note is that lightning and static protection for the antennas is yet another subject, but
this should always be kept external to the building and will not be covered here.
There are many good articles about correct station grounding both online and in all
of the usual publications on ham radio from the ARRL and RSGB etc. As the output
power increases this becomes much more of a safety factor and should not be
ignored!
This section is here only to inform the user that it is an important consideration that
needs to be addressed and whether or not it needs to be implemented.
The classical RF ground consists of a series of ground rods driven into the ground
over a suitably large area. Connected together with heavy gauge wire or strap and
situated as close as possible to the radio installation, to which every piece of
equipment has a heavy gauge wire or strap connecting it to the RF ground. Most
commonly this is done with copper wire / *suitable copper braid or copper tubing to
the ground rods that are usually made from copper or copper coated steel. If using
copper particular attention should be made to the fact that copper corrodes and as it
does will lose its conductivity properties so a certain amount of maintenance will be
required as time passes. (*note: copper braid stripped from coaxial cable is not a
good idea. If the cable is left intact with both the centre conductor and outer
insulation present it can be used as a single conductor for ground connections but
removing the braid will make for a poorer RF conductor and will allow corrosion to
commence. There are ready made braids that are manufactured especially for this
use).
The distance of the RF ground to the radio installation and also the length of the
individual connections from equipment to the RF ground are very important and
depend on the frequency of use. They must be made as short as possible and much
). At 6m this can be difficult to achieve as at 52MHz
less than a ¼ of a wavelength (
a ¼
is only 1.44m. If you have a ¼
of wire this will present a high impedance
and will impede the flow of RF to ground.
Antenna type, (balanced or unbalanced), fed with coaxial cable or balanced feeder,
proximity of the antenna to the shack, Antenna tuners and BALUNS etc all have an
effect on system performance and safety.
Typical examples are unbalanced antennas that cause RF to return back along the
outside of the coaxial cable screen and thus the equipment connected to it. This is
often described as 'RF in the Shack' and can cause many different issues, some
common ones such as tingling to the lips when touching a metal microphone grille,
or a tingling sensation when touching the CW key or metal chassis of the ATU /
23

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