You must use a balun
to balance your dipole
Date: March 28, 1995
Original source: Usenet's rec.radio.shortwave
By feeding the antenna with properly grounded coax you get
the benefit of a shielded lead-in, which will reduce electrical
noise pickup from near your house. Its usually signal/noise ratio,
not just signal strength, which is important.
This is true
only if everything is connected properly. You cannot just connect
co-ax to a dipole and then to your receiver and expect it to work
properly. A dipole is a balanced device, co-ax is an unbalanced
feeder and the inputs on most modern receivers are unbalanced.
You cannot just mix balanced and unbalanced configurations without
Consider that the signal induced in one element of the dipole
is 180-degrees out-of-phase with the signal induced in the other
element. A balun is required to reverse the phase of one
of the signals so that they are additive. Assuming the use of
twin-feeder line from the dipole to the balun it follows that
any noise (or signals) picked-up by the feeder will be in-phase
between the two lines and will, thus, be effectively cancelled
when the phase of one of the signals is reversed.
If you do not use a balun you end up with just a random-wire antenna
because the signal from one element of the dipole is just sent
straight to ground and contributes nothing. And if you use co-ax
from the dipole to the receiver without using a balun you can
get significant capacitive losses.
Many SWLs find that a "dipole" often gives no improvement or even
inferior results. The reason is usually because a balun has not
There is a great deal of misunderstanding concerning the function
of a balun with many regarding it as just an impedance-matching
device. A balun may well match impedance but it does not have
to - it can easily have an impedance ratio of 1:1.
What is important is that it matches balanced to unbalanced
lines. After all, balun is short for "balanced-to-unbalanced"!