Ramsey Electronics DA25 - Manual (Page 4)

DA25 • 4
INTRODUCTION
In today’s ever growing “wireless” society, it almost seems a bit ironic that
antennas have become less and less the topic of interest in hobbyist circles.
The recent advances in wireless technology have shrunk antennas to ever
smaller an unobtrusive sizes. An example of this is the cable television industry.
They have removed the larger “traditional” antenna arrays that were once
commonplace for TV reception and replaced them with a single wire or two
entering the household. Advances in the semiconductor industry have provided
engineers with the tools to pull the smallest signals from the airwaves with
better noise performance than could have been dreamed of when the
technology of radio reception was envisioned. Advances in satellite technology
have reduced the size of a reception “dish” from over 12 feet in diameter to a 1
foot round platform!
Antenna design certainly has not made the “quantum leap” that was brought on
with the advances in the semiconductor industry, but it is just as important as it
was in those early days of radio. The original aerials, or reception antennas,
had to provide enough signal to overcome the ever present noise and allow the
early receivers to detect and demodulate signals. These early antennas were
quite large (we’ll talk a little more about this later) due to the lower frequencies
being transmitted. Again, more recent improvements have allowed us to use
higher frequencies with significantly smaller antennas.
With less and less demand for consumer antennas, the market price of these
commodities has increased. As many of us have discovered, even the lowest
cost antennas run in excess of one hundred dollars! While they are necessary if
we intend to use the antenna commercially or for television reception, it simply
is too much for a hobbyist to invest for use with a monitoring receiver. Enter the
Ramsey line of discone antennas, allowing us to “tinker” with the airwaves at an
affordable price.
Ramsey Antennas 101:
Before we break open our discone kit, lets talk about what makes an antenna
tick, and some of the terms used to define antenna performance.
How Fast are Radio Waves?
If one were to “whip” the end of a taught length of rope, you could observe the
wave created traveling down the rope to it’s end. Going back to our physics
class, recall that the speed of any object is the distance it travels divided by the
time it takes to get there, or Velocity = Distance / Time. The time a wave takes
to travel is dependant on the type of wave and the transmission medium. The
wave in our rope example can take seconds to traverse down the length of the
medium. Sound waves travel about 1100 feet every second; if we called out