Choosing an antenna for your amateur radio station requires a little
logical forethought.  You should first decide what bands and modes you
want to work and then choose the antenna that will provide the best
performance for your particular operational situation.

There are many, many different antenna types and each one will provide
good performance, but this performance will be limited to the band(s) or
mode(s) for which the antenna was designed.  For example, some antennas
are designed for a single band while others are multi-band.  Some antennas
work DX well while others do not.

There are certain performance factors that will influence your selection
of one antenna over another.  These factors include gain, front to back
ratio, polarization, angle of radiation, bandwidth, and physical size.
It is best to take some time and learn the characteristics of each
antenna type before you choose an antenna.


VHF Antenna Scenario

VHF repeater work is the easiest way to explain this antenna type versus
performance/requirement correlation.  Let's start with a ham with an HT
that lives, as I do, close to the 145.47 repeater.  All I need on my HT
is a "rubber duck" antenna, which is an electrical 1/4 wavelength,
helically- wound, shortened 2 meter vertical antenna.  The important
factor here is "vertical."  FM repeaters historically have had their
antennas vertically polarized due to the fact that repeaters were
initially used to support commercial mobile VHF communication where
antennas are more easily made vertical to work against (in a good way)
the vehicle body.  VHF frequencies are polarization sensitive, so in
order to work into the repeater efficiently, I need to have a vertically-
polarized antenna on my HT.

Now what if I move my home QTH away from the repeater a few miles?  The
repeater signal received is still strong, but I can't get into the repeater
from inside my house due to the weak 2 watt HT output signal.  So, I put up
a J-pole on my roof.  A J-pole is a vertically polarized 1/2 wavelength
antenna.  I placed the antenna outside and in the line of sight of the
repeater so repeater operation with my HT from my new house is back to
normal and I am happy again.

But now I have to again move my QTH out 59 towards Wharton.  This time, I
am working on the extreme fringes of the repeater's operation, and both the
reception and transmission are very poor, if not non-existent, even with my
J-pole on the roof.  I then put up an 11 element high gain yagi, again
vertically polarized, on the top of my 50-foot tower I have up for my HF
yagi antenna.  I return again to normal operation into the repeater due
to the increased gain and height of the yagi.

Now, I can continue this scenario by moving further out and putting up
bigger antennas until I have phased/stacked yagi's on a 90-foot tower
running a receive preamplifier and a linear amplifier on transmit, but
I will stop here.  You get my point, which is that you have to apply
the correct antenna to the desired operational situation.  Of course,
you could put up a yagi while living in Houston right near the repeater,
but this would be overkill and money wasted.  However, if you wanted to
work other repeaters that are on the coverage fringe at your house in
Houston, you still may want to put up the yagi on a rotator to achieve
the necessary gain and directionality to work these fringe repeaters.


An HF Antenna Scenario
(My Sharpstown city lot QTH)

Most hams would agree that the most popular and useful antenna for HF
work is the rotatable yagi or quad beam.  These antennas, used mostly
on 20 meters and up, provide gain on both receive and transmit.  They
are able to be pointed toward the station or area to be worked, and
interfering signals off the sides or back of the beam will be attenuated.
Beams come in various sizes and configurations.  Some have 2 elements,
some 3, 4, or even 6 elements, depending on the physical size restrictions
of the support structure.  Most HF work is not like the above VHF scenario.
Most of the time, we are not looking for constant reliable communication.
What we are looking for is an antenna system that performs the best in the
propagation conditions that exist any time we turn on the radio.

HF Yagis are horizontally polarized and their radiation launch angle 
varies with their proximity to the earth.  If we want to work close in 
stateside contacts, we would probably place the yagi less than 1/2 
wavelength high for a high launch angle.  If we want a majority of DX 
signals, a yagi must be placed at least 1/2 wavelength or more above the 
ground at the operational frequency.  The higher up we place the yagi, 
the lower the launch angle; therefore, we can work DX that is further and 
further away.  So, my 50-foot tower with a tri-bander yagi at 50 feet works 
great for 20, 15 and 10 meter DX.  Monoband yagis would provide better 
performance, but I have to compromise due to my tower's wind load 
restriction.

Now if I also want to work the lower bands of, say 40, 80 and 160 meters,
I need to apply a little thought to my antenna situation.  Although beams
are made and used for these lower bands, they are big and actually too
large for my lot size and too heavy to support on my tower.  I therefore
need to utilize alternate antennas for these bands.  My low band antenna
farm design goal has the following criteria: 40 meters work DX, 80 meters
work both DX and local contacts, and 160 meters work local contacts.  40
meters DX requires an antenna that has a low radiation launch angle so that
my signal travels as far as possible before it is reflected back to earth.
On 80 meters, I need this DX low launch angle situation, but I also need a
high launch angle for the BVARC Ragchew Net.  160 is a high launch angle
situation.

On 40 meters, I decide to place a full-wave triangular delta loop hanging
vertically from my tower at 46 feet, just under the tri-bander.  The bottom
corners of the triangle are at 15 feet and are tied off to support poles.
By feeding the delta loop at one of the bottom corners, it will give me
vertically polarized, low launch angle radiation in an omnidirectional
pattern.  Loops also provide a slight increase in gain over a vertical
or dipole and they are inherently quieter than other antenna types on
receive.

On 80 meters. a loop would not fit under the yagi, so I decide to use my
tower as a top loaded (the yagi acts as a capacitive hat) 1/4 wavelength
vertical using elevated radials.  I feed my tower directly with the coax
center wire at the 10 foot level (an equation from the Low Band DXing book
helped me figure this 10- foot feed point), and then I connected four
elevated 1/4 wavelength (65') radials to the coax shield.  This "quasi-
inverted sloper" makes a fine 80 meter vertically polarized omnidirectional
DX antenna.  On receive, the noise level of natural static (QRN) on 80
meters is very high.  Vertically polarized, man-made noise is also received
just as well as signals.  Because of these noise factors, I decide to place
a full size (245') horizontal 80 meter loop mounted on poles at the 25 foot
level around my property line.  This loop makes a great low noise receiving
antenna for 80 meters (and other bands), and will also work great as a
horizontally polarized, high launch angle and ground wave 80 meter antenna
for local QSOs.

On 160, I only want a local signal, so I load my 80 meter loop as a long
wire through my tuner by removing one end of my feed line from the tuner
and let it hang loose (away from the tuner chassis, of course).  This is
a compromise, but good enough for the little ragchewing I do on 160.


Why?

So by now you're asking why different antennas for each band and why go to
all of the trouble?  Well, what I am trying to do is get the best compromise
between my operational goals, antenna performance, physical size and
compatibility with the other antennas, towers and support poles.

Yes, there are other antennas that will work.  For example, a multi-band
vertical will function nicely on 80 thru 10m, but I will get much better
performance with the individual antennas that I have chosen.  Verticals
are susceptible to interference from man-made noises and the city is full
of man-made noise.  A receive loop would be a necessary addition.  Now, I
could also use a multi-band 80 thru 10 wire dipole, but due to the
horizontal polarization the radiation launch angle is a function of its
height above the ground.  This dipole hung at 50 feet would be a good DX
antenna on 20 and above but the DX performance on 40 and 80 would suffer;
however, if you only work stateside contacts on these bands, this dipole
will work just fine.

So, in order to attain the best overall station performance, it is best to
spend some time beforehand thinking about the frequencies on which you want
to operate and what kind of contacts you would like to make.  Read a few of
the amateur or shortwave antenna books which are either available for loan
at the Houston Public Library, or for purchase at your local ham emporium.
Also, talk to your Elmer about the different antenna types.  Learn the
pluses and minuses of each antenna before spending your hard-earned cash.
If you have a deed restriction or physical space problem, there are other
antennas that can be put up.  They will be a compromise and not work as
well as the full size antennas, BUT they will get you on the air.

I hope this article has given you some insight into how to choose an antenna
by looking at your requirement(s), studying the different antenna types and
then selecting a skyhook that will provide you with the best performance and
the most fun from your particular amateur radio station.