Marshall Amplification Field 4000, Owner'S Manual

Page: 23 / 40

Page 23
Ow ner’s Manual
Advanced Telemetry
The Field Marshall Receiver is easy to use successfully for almost all
occasions. But there are those times when you will stretch it to its
limits. It will be worth your time to read this section and learn a few
more techniques. First we cover some theory on how radio works
which is essential if you want to find your bird or dog when it is really
lost.
Transmitter Patterns
The one thing telemetry transmitters all have in common is the an-
tenna. The wire commonly used on transmitters is known as a short
end-fed dipole. With this kind of antenna most of the energy radiates
from the side. It’s called broadside radiation and the pattern looks
like a donut, as in the diagram on page 27.
Little energy comes from the end of the antenna, so when the an-
tenna is pointed right at you, you get the worst possible signal. When
attached to the body of a dog, the dog’s body acts as part of the an-
tenna and alters this pattern in unpredictable ways. The pattern then
will not look like a donut, but maybe more like a partly inflated beach
ball. There simply is no flexible antenna that radiates equally in all
directions.
Hint:
When your bird or dog is out of sight, the donut pattern can
tell you much about its movements. Listen for the signal fading in
and out as the it moves around, alternately pointing the antenna to-
ward and broadside to you. You can also tell when the antenna is
near the ground or vegetation by changes in the strength of the sig-
nal.