Ham Station Desk Radio Equipment Ground

Ham Station Desk Radio Equipment Ground

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Coaxial cable leakage

Consumer Gear RFI


Station ground lightning and safety

House ground layouts

Contest station

lightning and safety
and entrance wiring

ground resistance
measurements on
small 160 meter

Ground Systems

Common Mode Current

includes dipole

Receiving Common
Mode Noise
how lack of a balun
can contribute to
system noise (it
applies to
antennas as

Long wire
antenna random wire

Second Floor Grounding

RF in the Ham

It is commonly
assumed “RF in
the shack”,
interference to
consumer devices
like telephones or
stereos, or even RF
feedback or RF burns result from poor operating
equipment grounding.
There is also a
that a good equipment RF ground improves our transmitting signal strength,
and the lack of an
RF ground causes poor
reception. Another
popular belief is
each piece of desktop
equipment needs to
have separate leads
to a grounding point, so
RF doesn’t move from
the chassis of one
piece of gear to
the chassis of another through daisy-chained cabinet grounds. Sometimes
we read that beads or isolators
are recommended on
coaxial cables
running between
pieces of equipment.   Like most of us do at one time or another, I
strongly believed in RF
grounds on my desk.

The beliefs
above are actually
not true except in
very specific (and
installations! Eventually I learned RF grounds, very often,
didn’t do anything
but mask more significant system

What Causes RF
Problems in

 In a perfectly engineered world, strong RF fields would not bother anything except
devices made intentionally responsive to RF energy. Blame for RFI ultimately
lies with the device that is not supposed to be affected or controlled by RF
being responsive to RF. There are five reasons RF problems appear:

1.) The antenna
system has a design,
engineering, or
installation flaw

2.) The antenna is
too close to the

    3.) The problem is not RF at all, but is a DC power
supply ground loop back into the audio system

    4.) Equipment has a design defect

    5.) We have poorly
installed connectors or defective cables

or when is a ham station
ground necessary?

Sometimes we set
ourselves up for
problems without
knowing it.

  • Antennas with
    high levels of a
    phenomena called
    can bring
    a great deal of RF
    back into the
    shack via the
    feed line
  • Certain types
    of equipment with
    improper enclosure
    design or improper
    interconnection design
    create problems. Examples are poor ground terminal path implementation at the
    connector’s cabinet entrance
  • Some equipment
    is not designed
    properly on input
    or output ports, and
    the poor
    port electrical design creates
    or aggravates problems. Example are excessively low voltage threshold on
    control lines
  • At times our antennas
    are too close to
    the operating
    position, causing every
    wire in the house
    become a
    receiving antenna
    and a potential
    source of unwanted
    strong RF
should not
assume distorted or
bad audio is always
RF feedback or RF
related problems.
Sometimes it can be
direct current
ground loops in
station audio that
allow power supply
current load
variations to
modulate the
transmitter. Audio
lines that route
from one piece of
gear to another
should always be
grounded through a
chassis ground path
only at one end of
the cable. For
example a microphone
input has a ground
inside the radio. If
an external device
is connected to the
mic jack, and that
external device
grounds the mic
shield back to the
station ground or
power mains safety
ground, it will
introduce hum into
the audio. If the
12V power supply is
similarly grounded
(as it should be) to
the mains safety
ground, audio-rate
modulation of the
12V supply can be
coupled back into
the mic input shield
and modulate the
transmitter. This
distortion sounds
very much like “RF
feedback”, but it is
an audio shield
ground loop issue.
In the
professional audio
world this is
called a


This is more than
an audio line
Manufacturers can
also put a “pin 1
problem” into
power supply and
control lead
connections. THE
12 volt POWER

causes equipment
cabinets to be hot
with RF, a change
in noise, a change
in RFI, or a change
in SWR when
a ground is
connected or removed

If connecting or
disconnecting a
operating position
ground causes a
change in noise
level, SWR,
transmission, RFI,
or TVI…..your equipment
has significant RF
flowing over the
wiring or cabinets. This type of
unwanted current is called
current .

Common-mode current is not
flowing inside a
cable shield, or flowing as a properly balanced-current in a
parallel wire
feed line.
Common-mode current is
like currents causing antenna
radiation. Common mode
flows on the outside
of shields, or appears as an
imbalance in phase
and/or current level in multiple parallel

Common-mode current

What sounds like RF feedback usually is RFI, but other things can sound very
similar. We should never
assume distorted or
bad audio, or other anomalies during transmission, are always RF feedback or RF
generated problems. An “RFI” problem might be
direct current
ground loops in
station audio wiring, or in control wiring. These unwanted dc currents can cause
SSB power supply
current load
variations, which vary at an audio frequency or CW keying rate, to
transmitter audio lines or control lines.

lines routed
from one piece of
gear to another, if that equipment is not locked to the very same dc or low
frequency cabinet potential,
should always be
grounded through a
chassis ground path
only at one end of
the cable. For
example a microphone
input normally has a ground
inside the radio. Ideally that ground should be at the connector entrance, but
often it is located up on some board near an audio preamplifier. If
an external device
is connected to the
mic jack, and that
external device
grounds the mic
shield back to the
station ground or
power mains safety
ground, it will
introduce hum into
the audio. This is called a ground loop. If the
12V power supply is
similarly grounded
(as it should be) to
the mains safety
ground, audio-rate
modulation of the
12V supply can be
coupled back into
the mic input shield. Current flowing on the shield to the radio causes a
longitudinal voltage drop along the mic cable, and that voltage will modulate the
transmitter. This
distortion sounds
very much like “RF
feedback”, but it is
an audio shield
ground loop issue.

A second problem
is poor design of
some devices, in
particular external
audio interface
devices. Not only
should external
systems isolate
shield paths with
suitable audio
transformers, if
they contain
semiconductors they
should employ
properly designed RF
bypassing. Many
devices do their
intended audio
frequency job very
well, but are
designed for use in
high RF fields. Devices noted for causing ground loop problems include cheap
computer sound card interfaces, and some external station accessories, such as
microphone switches. 

I have this problem with multiple headsets at multiple operator position,
when I do not float the audio lines with isolation transformers.

RF Isolators and Beads on RF Cables

RF isolators and beads on coaxial lines 
modify common mode impedance on the outside of cable shields. They accomplish
this by allowing a voltage difference to appear longitudinally across the bead
or choke. In effect, the cable shield going into the isolator or string of beads
floats at a different RF potential to ground than the same cable shield exiting.

It is almost never a good thing to have potential
differences across cable shields on a desk full of lower-level lines. The only
thing that can be accomplished is shifting of current from heavy coaxial lines
to smaller lower level signal lines.

Typical transmitters, amplifiers, antenna switches, and antenna tuners do not
create noticeable
RF currents on the outside of shielded cables. Harmful outside currents never appear with properly installed connectors, wiring, and equipment cabinets.
If we have bothersome or significant RF currents in our shacks on the outside of
interconnecting RF cables, we really should learn why the RF is there and
correct the real problem. We should correct the real problem because it is an
abnormal problem that should never appear.

shielded enclosure


Generally coaxial connectors are bolted to major
areas of sheet metal that form one of the cabinet walls.



RF between gear


With connectors properly bolted to a cabinet
metal wall, all currents stay inside the  enclosure. If there are any
outside currents on transmitting cables between cabinets, and we add beads or
isolators, we simply shift those currents from cable A to cable B.

As a general rule any currents are either
generated outside the desk system, or are a result of poor connector
installation or poor cabinet design. On HF or VHF, cabinets do not need to be
“RF sealed”. As a matter of fact, an arrangement with RF paths closely spaced
over a good groundplane can be just as effect as a totally enclosed housing.


The important point is if we do have a problem
with RF outside cables, we should learn why that happens and correct it.  The last thing we should do is float shield
ground connections (which is what the outside of the shield provides) between
different pieces of equipment on our desk. The most we can expect from isolating
the outer shield path with isolators or beads is relocation of unwanted currents
to other cables and wires
between gear. Beads over transmitting cables or isolators on RF cables between
major equipment isn’t a good idea.

Equipment behavior changes, observed by moving wires around, changing grounds to
the desk ground, or changing outside shield impedances, indicate a problem with
connector mounting, shield connection impedance, or cabinet design. As for
equipment, there are a few cases of terrible cabinets. At least one commercial
antenna tuner has an intentionally insulated cover. Another tuner tuner uses a
single-core 4:1 current balun that forces balanced output lines into significant
voltage unbalance. No one can dispute there are occasional serious errors in
equipment design, but the real fix is correcting the design error.

The correction for those and other errors is not in grounding connections to a
ground buss, or adding isolators or strings of beads. The proper fix is
correcting system defects. Otherwise, when we throw an isolator or beads on
cables, we simply move the problem someplace else in the wiring where it waits
to cause problems in the future.

Isolators have a place in the world of antennas and feed lines outside the Ham
shack. They can be important when a system is neither perfectly balanced
nor perfectly unbalanced. Marconi verticals with less than perfect grounds are
examples of systems operating in the netherworld between perfectly
unbalanced and perfectly balanced, where isolators legitimately help. But in
cases like this, we want isolation that allows voltages to be different along a
section of coaxial cable to be OUTSIDE the house, not inside the house where
noise and devices sensitive to RF live.

Inside the house, we really want all cabinets and
device chassis to have the same RF potential. We do not want to isolate cabinets
from each other, intentionally allowing them to float to different RF potentials
to each other and to ground. If throwing beads or isolators on an RF line inside
the shack changes something, that line has a problem that needs fixed or at
least needs understood. 

The only beads in my shacks on any RF cables are
on receiver leads that have phono plugs, because the layout of the plugs and the
shield connections are less than ideal. I live with those connections because
that is the type of connector used. I understand what the problem is and choose
to work around it, and I keep an eye on it.

A shield connection similar to the picture below, with the
connector mounted on an insulated or isolated panel, can increase
shield leakage by at
least 40 dB at 7 MHz.

poor shield connection method absent metal panel







I can’t imagine having connections like this on a 100-watt transmitting line,
let alone 1500 watts. Transmitters deserve real connectors mounted properly, and
cabinets with RF integrity at joints. What we do inside the box doesn’t mater
much, but ground entrance method is significant.



















What causes
common-mode current?

Current flows
when there is an
electrical potential
(voltage) difference
between two parts of
a system, and a
conductor between
those point to carry current.
There are also
special currents,
without actual
electron movement,
called displacement
currents. Displacement
currents flow
through capacitor
dielectrics, between a
vertical or single
wire fed antenna and
for that antenna, or
between a mobile
antenna and a car
body. Any two things
that have
capacitance between
them can have
currents flowing
through that

currents commonly
complete the current
path in open-ended
antennas, although
all antennas have
currents are the
reason an open-ended
antenna like a
dipole, longwire, or
vertical is able to
have current flowing
out to the antenna
end, even though the
insulated end just
hangs in the air!  They
are also one of the
reasons current
tapers in an
antenna, instead of
being equal through
the entire length of
the antenna. This
displacement current
has to somehow get
back to the
feedpoint, and is a
major cause of
currents. There are
several other
causes, but they
involve more easily
understood circuit

The amount of
current is dependent
on path common mode
impedance and the
source and
This is why some
people claim ferrite
beads work wonders,
and why other people
claim the same very
beads won’t work.
Band-aide patches,
like peppering a
flawed installation
with beads to
correct a problem
caused somewhere
else in the system,
are very system

The feed line

If you are not
familiar with how
coaxial cables work,
you might want to
look at a
simple  explanation
on this site
one of the ARRL

In order for a
conductor (like the
outside of the
shield) to not have
current flow at
radio frequencies,
it must have the
same electrical
potential and phase
all along the
length. If it has a
high series
impedance (common
mode impedance) or
if the potential
difference along the
conductor is low,
very little current
will flow. As seen
in coaxial cable
descriptions, any
coaxial feed line can
have unwanted common
mode currents. 

Does a vertical
or longwire present
high common mode
voltages to the
feeder that can
cause common mode
currents? You bet it
does! The only
vertical (or
longwire) that would
not cause such
problems is one with
a very good or
nearly perfect
ground system, and
that means something
that electrically looks
or behaves like an infinite
groundplane. Even
then, the cable must
exit below that
groundplane to be
“shield current

Most excessive operating position RF level problems
are caused by the
antenna system

Bringing a

longwire or some
other single wire
feed system

directly into
the operating
position will
high levels of RF
in the station. This
is because, unlike
two-wire balanced
lines or coaxial
cables, a single
wire feeder has no
other terminal or
return conductor to
“push against” for
currents flowing to
and from the
antenna. Longwires,
random wires,
inverted L’s, true
Windom antennas, or
any other single
wire “feeder” or
antenna require a
desk RF ground
connection. When
such antennas or
feed lines are
brought into the
shack, they also
bring grounding
problems to the
area. Another troublesome
antenna is the OCF
(off center fed)
dipole. It is an
antenna with severe
common mode
problems, even
though it has a


verticals are

for common-mode
currents also,
because they lack a
proper ground. A
vertical is most
often an end-fed
antenna. Sometimes
the element is 1/4
wave, at other times
1/2 wave or 5/8th
waves long. If we do
not use a perfect
“zero impedance”
ground system,
vertical antennas
can excite their
feed lines with
significant common
mode current.

An RF ground for house
equipment is
never required when
using properly
two-conductor lines
such as coaxial
cable or open
wire transmission lines. With

coaxial or
feed lines,  the
operating position
should have minimal
RF levels even
when a
shack or desk ground
is totally absent! My
present stations do
not have RF
grounds at the desks
or inside the room,
as was also true for
every one of my
stations since the
later 1970’s. 
I have used
desk-top safety grounds
with older gear,
specifically older 120V-operated vacuum tube
transmitters and
receivers (you’ll
understand why
later), but that is
always for safety
and not for RF

If you have
two-conductor feeders,
either in
the form of standard
coaxial feed lines or
lines, and have RF
in the shack or see
a change in noise
level, transmission,
reception, TVI, or
other problems
when a station
ground is connected
or disconnected, you
really have a
different problem. If you have
RF problems and have
good cabling between
various pieces of
gear, it is probably
not a ground
connection problem.
Your antenna system
feed line or other
conductors entering
the shack 
probably have

common mode currents
.   The sole exception
to this is
when single wire
feeders are brought
into the desk area.

Log Periodic Antennas
and RFI

One problem I
have helped two or
three people with is
their improper
routing of coaxial
cables on their


log periodic
In all cases they
were trying to cure
severe RFI and “hot
cabinets” in the
radio room with
chokes and beads and
grounding. The real
problem was at the
antenna. With the
antenna feed
corrected, their
problems went away
without suppression
beads in the shack
or RF grounds in the
Ham shack.


In the case of a
dipole antenna, each
feedpoint terminal
has “voltage to
earth”. If a
balanced dipole has 100 volts across the feed terminals, the feedpoint would have
about 50 volts to an imaginary groundplane
bisecting the antenna





The current
pattern to the left is for a 1/2 wave dipole 1/2 wl above ground, with coaxial
feed. You can see the feed line shield has significant current. In this case
about 40% of the antenna’s maximum current!






We can simulate a choke balun by adding a current source in series with the
shield and setting current for zero amperes. The voltage across that current
source will indicate the common mode voltage exciting the feed line.


Adding a perfect choke balun, current on the feed line shield goes to zero and
the voltage across the choke balun is now found from the source menu:

Source 1 Voltage = 61.02 V. at -0.01 deg.
Current = 1 A. at 0.0 deg.
= 61.02 – J 0.009274
Power = 61.02 watts

Source 2 Voltage = 37.42 V. at 173.27 deg.
Current = 0 A. at 0.0 deg.
Impedance is infinite
Power = 0 watts

Source 1 (61
volts) is the actual terminal excitation of the dipole, while source 2
(37.42  volts) is
the voltage that
would cancel common-mode feed line current. We can see the voltage
across the perfect balun is indicated by source 2 as 37 volts.
This is slightly more
than 1/2 the feedpoint differential voltage. (We could also use a very high
impedance load in
the feed line of the
model and show the same thing.)



This is a
substantial amount
of shield
excitation. It is
easy to see how a
dipole without a
good balun might
cause RF problems at
the operating desk.
We fix this by
“grounding the heck
out of the station”,
but the real cause
and best cure would
be fixing our
antenna. by the way,
a few turns of coax
on an air-core form
is not a good balun
at all. It takes
almost 15 turns 4″
in diameter to make
a good 40 meter
balun, and the
impedance is mostly
reactance. The choke
location has to be
carefully planned
when using an
air-core balun.
Depending on cable
lengths and balun or
choke location,
adding an air core
balun or choke can
even make things
worse! If we use an
iron core with a
high loss tangent,
most of the
impedance will be a
resistance. This
will increase common
mode isolation over
a much wider
bandwidth. A high
resistance low-Q
balun is much better
for bandwidth and
much less critical
for location in the

Dipoles, even
though balanced
antennas, can have
problematic common
mode currents when
fed improperly.
Without a balun some feed line
lengths can cause
problems, while
other feed line lengths
can actually eliminate need for a
balun. One popular
balun and unun
handbook claims a
dipole does not need
a balun because the
feed line is a very
small diameter in
wavelengths. That
isn’t true at all.
The author tested
the need for a balun
while using a 1/4
vertically handing
feed line, a case
where his choice of
feed line length just
happened to
eliminate the need
for a balun. It was
nothing to do with
the feed line
diameter being

There is no
universal magic
feed line length that minimizes
common mode currents
in every
The length required to minimize
common mode varies
with feed line routing,
grounding, and
surroundings. If we have
a very specific
like a vertical
feed line hanging
vertically in open air from a
dipole center, and
that feed line runs
straight down to
earth and is grounded
at earth’s surface,
we can predict the
feed line length to
minimize common mode
without a balun. The magical
length in this
specific case is 1/4λ or any
odd quarter
wavelength of cable
length between the
antenna feedpoint
and ground. Since
the primary
dielectric between
the cable shield and
earth or the antenna
is air,
feed line velocity factor
is meaningless
If we inserted a
common mode choke
right before the
ground on the
antenna side of the
ground, it would
maximize common mode
problems! We have to
be careful throwing
parts at a system
hoping something
will stick.

with less than

Here is a model
of a groundplane
with four radials:

EZNEC ver. 3.0
Balun 80 vertical
1/3/04 7:19:05 PM
Frequency = 3.6 MHz.
Wire No.
6.700 (antenna
Wire No.
1.359 (This is your
feed line or mast)
Wire No.
1.985 (radial)
Wire No.
1.985 (radial)
Wire No.
1.985 (radial)
Wire No.
1.985 (radial)

We can see
significant current
flows over wire 2,
which would be the
coax shield, a mast,
or both. 



There is a trick
we can use with Eznec. By
inserting an
additional source in
the mast or feed line
and setting current
to zero, we can
observe the radial
common point to
earth voltage
required across a
balun to force
current to zero. In
this case the
voltage across the
balun would be:

Source 2 Voltage
= 145.5 V. at 67.97
Current = 0 A. at
0.0 deg.
Impedance is

Amazing isn’t it?
At 1500 watts the
ground common point
for the radial
system actually
wants to have 145.5
volts to earth
prevent current flow
along the outside of
the shield!! If we
elevate the common
point to 145.5 volts
at 68 degrees phase
angle, we now have
the following
currents at 1500

Wire No. 1: 6.4 A
(antenna element)
Wire No. 2: 0 A
(coax shield or
Radials: 1.58 A each
(antenna radials)

How many times
have we been told
four resonant
carefully tuned
radials make a
perfect ground? Obviously
any claim four
radials form a
perfect ground is
not true. If it was
a perfect ground
center point of the
radials would be at
zero volts. With four radials
the antenna is not
Since the antenna is
not perfectly
unbalanced, some feed line
lengths or grounding
will allow appreciable
current to flow over
coax shield.   

Is it any wonder
we have RF problems
with some of our


End-fed antennas,
be they so-called
“end-fed dipoles”,
zepps, or longwires
all offer a very
good chance of
having RFI problems.
They might require
multiple stages of
feed line decoupling
to reduce
in-the-shack RF
problems.  You
can see some
examples of problems
they create by
looking at my page

fed zepps and other
end fed antennas

Other Systems

Windom antennas
produce considerable
common-mode because
the antenna is
neither unbalanced
nor balanced. They
require special
techniques, such as
a very good current
balun  or a
combination of
current baluns and
other choking

Full-wave loops
operated on their
frequency generally
don’t create
problems, but they
can when operated on

Eliminating Common
Mode Problems

We commonly hear
that a few turns of
coax on an air core
form makes a good
balun or device to
cure common mode
currents and RFI
problems. This just
isn’t true in most

Even if we use
enough turns to
provide a high
reactance, which
many suggested
baluns of 5 to 10
turns do not, the
resulting reactance
is generally
inductive on lower
bands. Depending on
the common mode
impedance of the
system the balun or
choke is inserted
in, the reactance
can do anything from
reduce current to
greatly increase
current. I use
ten-to-twenty turn,
4″ diameter, air
core choke baluns on
some of my yagi
antennas. I locate
them right at the
balanced feedpoints,
I tape the coax
leaving the choke
balun to the boom, 
and I use a barrel
connector as a
connection point to
the feed cables
running down the
towers. I ground the
barrel connector to
the antenna boom.

This establishes
a very good
reference point for
common mode
impedance. I know
the common mode
impedance at the
connector is
reasonably low
(because it is
grounded to the boom
and tower), and I
know any series
inductance, will
greatly decrease
common mode

F12 antenna baluns


Typical of my
Force-12 Yagi baluns





The balun system
above works with any
Yagi, and it even
works when used with
dipole antennas. My
160-meter Inverted
Vee dipole has a
similar balun
system, with the
connector grounded
to the tower.




Outside Entrance

house shack ground cable entrance outside




All cable shields are
ground to wide
copper flashing.
This means there is
no RF current
flowing between
shields inside the


The wide copper
flashing exits under
the house directly
to the mains
entrance ground for

provides a low
impedance shunt to
ground for any RF on












Inside Entrance
Panel and Common

inside radio room ground entrance common point


Left to right:

Receiving antenna
trunk selection

Control cables

Power SWR sample

Antenna trunk switch





Small green
connector is
receiving antenna
directional control



This is double
protection. Any
current flowing
between shields is
minimized before
reaching the
operating desk.







Most, but not
all, RF in the shack
problems are caused
by poor antenna
implementation. It
is best to mitigate
any problem at the
problem’s source.
Notice the cures
above did not talk
about the RF
grounding quality.
The real cure is
keeping things at
the same potential
and keeping unwanted
currents outside the



I think the above
explanation is a
priority. If I left
anything out of this
or confused you,
please let me know.
I might not have
time to answer
e-mails but I will
do as much as I can.
You can email me at: