[Antennas] How important is the ground?

Sat May 21 13:45:52 EDT 2005

There are 4 different purposes for a ground connection to a radio.
1. electrical safety. This only applies if you are connected to a power
source that may seek to get to ground through the radio. i.e. a commercial
AC main, or a generator that is properly grounded. If you run a charger on
the battery while you are in the house you should have a ground connection
that ties the rig case back to the same ground as the electrical system for
your safety.
2. lightning safety. This is meant to keep the radio chassis voltage as
close as possible to the supply voltage and antenna voltage. By proper use
of lighting arresters on each lead all tied to the same single point ground
the voltage difference between various lines is minimized and so should
prevent damage to the equipment or operator.
3. antenna rf return path. If your antenna is not a balanced one like a
dipole then some of the return path for rf may be through the ground back to
the feed point. say you run a random short wire just stuck in the antenna
jack on the back of the radio with no ground... just like any other current
source any power that goes out on the center conductor of the coax connector
must come back on the shield. This can be looked at kind of like a big
capacitor. if you draw the field lines from one half to the other half of a
dipole they are nice and symmetric... however if you do it for the wire
stuck in the coax connector all the field lines from the wire end up
terminating on the radio case. Ok, so this works fine in free space, but
close to the ground lots of those field lines go into the ground along the
surface and the capacitively back to the case of the radio... unless of
course you get in the path between ground and the radio case, in which case
you get rf burns. You can minimize this by providing a counterpoise to act
as the other half of the antenna and/or providing a more conductive path
than you from the ground to the rig, in this case a ground rod.
4. rfi rf return path. This is similar to the case above, but in this case
the rf is the noise that is radiated from nearby devices. Just like your
transmitted rf this noise is being transmitted by whatever is around you.
If your radio/feedline happen to pick it up that current is going to look
for a path back to the source. Now, if you don't have a ground it can't go
that way, so it goes up to this big capacitor up above where it finds its
way back into the receiver on its way back to the source. If you do provide
a ground that MAY be the lower impedance path and 'drain' the noise off the
system before it gets to the receiver. Note that the 'MAY' means that it
depends on the source, location, orientation, etc of the noise. You may
find cases where adding a ground increases the noise because it provides
another path to ground through the radio. Making sure everything that can
make noise is grounded to a single point ground system helps by making a
common point for all radiated junk.
Note that all of these 'types' of grounds work the best when designed
basically the same way. The shorter, fatter the conductor the better, and
all equipment must connect to the same ground point.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

> -----Original Message-----
> From: antennas-bounces at mailman.qth.net [mailto:antennas-
> bounces at mailman.qth.net] On Behalf Of Buck - N4PGW
> Sent: Saturday, May 21, 2005 13:15
> To: antennas at mailman.qth.net
> Subject: [Antennas] How important is the ground?
>> I have an IC-706 mkii that I operate as a base, mobile and portable. When
> I
> moved it from my car to my house last night, I followed my usual routine
> of
> hooking up the antenna tuner, two-meter antenna, power and ground. It
> suddenly occurred to me that when I have been operating portable, I
> haven't
> been using any kind of ground.
>> For portable operation, I have been using a dipole antenna fed with an
> antenna tuner. The radio is powered on the same marine battery I use at
> home for a power supply. At home, however, I have lots of RFI from
> computers, appliances, etc. that give me an s-5 noise level if I don't
> ground the rig. Because of the noise level without the ground, I cannot
> test to see if the ground makes a difference on the received or
> transmitted
> signal or not.
>> Would I be better off to carry along some form of ground rod for use when
> portable? I have been setting up on a picnic table and operating with no
> consideration of ground since the dipole doesn't need one.
>> Thank you,
> Buck
> N4PGW
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