Low band DX season is just around the corner, so it is time to get things
set up and tuned up for winter time DX'ing.


DX versus Local Performance

Antennas may be broken down into many categories.  For this article, let's
look at antennas as DX versus local performance.  The differentiator between
local and DX performance is the radiation angle.  This is defined as the
angle, referenced to the earth, at which your transmitted signal leaves
the antenna.  For local or close in contacts up to 1,000 miles or so, a high
angle of radiation (straight up) is needed.  The transmitted energy travels
up to the ionosphere and is reflected right back down to the earth.  DX
requires a low angle of radiation in that the transmitted signal travels
a long distance towards the horizon before being reflected by the ionosphere
back toward the earth's surface again.

A single reflection of a signal between the earth, the ionosphere and back
to earth is called a "hop."  The signal's field strength is attenuated with
every foot traveled through the atmosphere.  High radiation angles give us
short hops and low radiation angles give us long hops.  High radiation angle
energy can make it to the DX, but because many more hops are required to get
there, the signal will be weak or non-existent.  If we can make the signals
go furthest with the least hops, we will have less attenuation and hence the
strongest signal at the DX end.  Low radiation angles give us lower
attenuation of our signal, but how do we generate this low angle of
radiation?


Horizontal Antennas

An antenna will exhibit differing characteristics based on the deployed
location.  For example, a horizontally-polarized antenna, such as a dipole,
has a radiation angle that is dependent on its height above ground.  Any
antenna book will have charts that give these radiation patterns to antennas
that are 1/8, 1/4, 3/8, or so wavelengths above the ground.  You will see
that as the antenna height above the ground is increased, the radiation
angle gets lower and lower.  A 10m, horizontally-polarized, dipole antenna
exhibits low angle radiation at about 16 feet above the ground.  Translate
that down to 40, 80 or 160m, and the height of the dipole becomes 65, 130
or 260 feet above ground.  Piece of cake, right?  Just build yourself a
low-band dipole and, depending on the band, hang it at 65, 130 or 260 feet,
respectively.  Not exactly an easy task for most of the hams I know.


Vertical Antennas

Horizontally-polarized antennas can cause a large logistics problem on the
low bands, but with apologies to the cat lovers there is more than one way
to skin a cat.  DX wise, it is called vertical polarization.  This type of
radiation is generated by vertically-polarized antennas such as ground
planes, monopoles, 1/2 wave verticals, 5/8 wave verticals, delta loops,
quad loops and other antennas.  Vertical polarization is the only way to
achieve low-angle radiation from an antenna that is close to the ground.
Yes, there are those rare occurrences that hams have worked a BV in Taiwan
on 15m with a 40m dipole laying in their spouse's vegetable garden.  But,
what I am talking about is consistent, low-angle DX performance that you
can count on day in and day out.  For working DX on the low bands, the
best antennas to use are those that are vertically polarized.


Vertical Problems

Vertically-polarized antennas come with a few compromises.  Man-made noise,
particularly of the RF interfering variety, is vertically-polarized and
WILL(!) get to even the best of the receivers made today. If you chase
DX, you will find that it is better at times to use a vertically-polarized
antenna to transmit and a horizontally-polarized antenna to receive.  A
horizontally-polarized antenna close to the ground will receive the DX.  
The signals won't be as strong, but the noise that you hear on the 
vertically-polarized antenna won't be there either.  Thus, your 
signal-to-noise ratio improves drastically, enabling you to hear the DX.  
Therefore, it might take 2 antennas to work some of this DX that is going 
to start coming through in the next few months.

Some people use three or more antennas because not every antenna is great
for all of the DX.  DX stations located at different distances have
different characteristics, so you need different antennas to have the best
chance of working them all.


The Ideal Antenna Farm

To bring this to a conclusion, I will state that you don't want to "place
all of your eggs in one polarization basket."  If, in any way, you can get
up an efficient, vertically-polarized antenna such as a full-wave loop, a
top-loaded 1/4 or 1/2 wavelength monopole, a Cushcraft R7, or a Butternut
1/4 wavelength vertical, etc., you will be better off.

On the receive side of things, a shortened dipole, a helically wound dipole,
a horizontal loop or even a coaxial loop will provide you with a lower noise
atmosphere on your receiver so that you can hear the DX through the noise.
A two-position coaxial switch will allow you to switch between the vertical
and horizontal antennas and chose the one that does the best for the
particular DX circumstance.  Have fun working low-band DX this winter.
This is the time in the sunspot cycle to chase it, as more people move
to the low bands due to bad propagation on the higher bands.

A final note. I wish to thank Carl WB8SVR, for his enthusiasm and effort
these past months as President.  I, as a newcomer to B-VARC, think he did
a bang-up job, and I wish him well with the Big X up there in W8 land.
When we finally find out his departure schedule, we'll arrange some HF
sked times and keep him entertained (or should that read, he'll keep us
entertained, Louis?) during his mobile trip north.

               CUL CARL HVE FUN ES GUD DX BT
               73 DE KF5NU (now W5RH).