Marshall Amplification Field Marshall 100, Field Marshall 4000, Field Marshall 800, Field Marshall 1000 Owner's Manual

Owner’s Manual

OWNER’S GUIDE

Page 1

Field Marshall Tracking Receiver

Contents:

Introduction........................................................................ 3

Getting Started.................................................................. 4

Receiver Controls ........................................................6-11

In the Field—A Quick Tutorial ..................................... 12

Frequently Asked Questions ........................................ 16

Advanced Telemetry ...................................................... 23

Radio Propagation.......................................................... 28

Tracking Strategies ........................................................ 34

Warranty .......................................................................... 40

Page 2

Owner’s Manual

Introduction

Congratulations on your purchase of the all new digital Field Marshall receiver.
It combines superior range and convenience in a compact and rugged design.
The Field Marshall is great for tracking Marshall Transmitters under any condi-

tions (see page 37).

- More frequencies (100, 800, 1000, or 4000 frequency models).

- Broad and smoother tuning.

- Increased range (more than any other receiver, and equal to
the Marshall Stealth).

- Much less noise and static interference

- Pinpoint accuracy (to within inches of the transmitter).

- Omni-directional sound.

- Smaller, narrower size.

- More rugged antenna design.

- Quick-Release handle.

- Improved range detection.

The digital Field Marshall won’t sound like your old receiver, because it has
unique Polyphase Filters that dramatically reduce the background noise. The

quietness means that you will hear the desired signal crystal clear and be able
to keep the volume down without blasting your ears with noise.

This quietness translates into better range and increased speed in finding your
transmitter.

Page 3

Field Marshall Tracking Receiver

Introduction, cont.

“The Quiet One” comes through with a more effective and pleasant
tracking experience.

The Quiet One

™

When you turn on your Digital Field Marshall, you’ll notice the
quietness immediately. You usually won’t turn it up as loud as

your old receiver because you don’t have to. While other
receivers are producing lots of noise, the new Field Marshall is

producing more signal.

How does the digital Field Marshall’s lower noise translate into better range? Well,
the answer is that with all receivers it’s the noise floor of the receiver that ultimately

limits its range. Any receiver can amplify a weak signal from a faraway transmitter.
The problem is that when you turn up the volume to amplify that weak signal the
noise just gets louder as well and continues to overpower the signal*. That’s why

the difference between a mediocre receiver and the best receiver is sophisticated
filtering and expensive electronic devices that minimize noise. It turns out that’s the

only way to increase the range of a receiver. Other receivers simply make a loud
sound, but loudness alone means nothing in terms of range.

* The technical term for the sensitivity of a receiver, or its ability to discern weak signals, is
the signal-to-noise ratio. A higher signal-to-noise ratio translates directly into better sensi­tivity and range, regardless of how loud the actual output of the receiver is.

Page 4

Owner’s Manual

Getting Started

The first thing to understand is how to deploy the collapsible yagi antenna,
which is a full-size three element Yagi Antenna for maximum range and

pin-point accuracy, using Marshall’s patented design.

Remove the receiver

from whatever carrying case you
are using (hunting bag, holster or

First, remove you r receiver from your

field holster or backpack.

1

carrying case) and hold it pointing away.

Push forward on the rear

2

(instantly!) flip out into the open position.

Warning: to avoid injury be sure to keep a

careful distance from your face or
others when performing this procedure.

loaded elements will automatically

of the slide bar.

The spring-

Second, push forward on the rear of

the slide bar to release the spring­loa ded elements out in to po sition .

Lift the Center Elements

up and out of their slots one at a
time and let them spring open

.

3

G E T T I N G S T A R T E D

Ne xt, lift the ends of the center

ele ments, one at a time, up from

their notched holders. They will pop

out i nto their correct p ositions.

Page 5

Field Marshall Tracking Receiver

Reach forward and

extend the forward elements until it clicks into place.

4

M

E

R

picture above.

To collapse the antenna, follow the same steps in reverse:

G E T T I N G S T A R T E D

Finall y, pull the director e lements ou t forward until they click at their ex-

tende d position. The yagi is now fully e xtended and ready for use.

The antenna won’t give its best range and pin-point

!

R

E

B

M

E

accuracy unless fully deployed as shown in the

- Slide the Slide Bar with the two Forward Elements
back toward the receiver.

- Rotate the Center Elements into their collapsed

position.

- Rotate the two Back Elements and click them into their

silver clips.

pull the slide bar forward

to fully

Page 6

Owner’s Manual

Turning It On

The receiver is turned on by rotating the Volume Knob on

5
6

They indicate the kilohertz (KHz) of
the frequency.

The frequency of the receiver is
very accurate (within one KHz) but

to get the best tone may need to set
the frequency 1 to 3 kHz above or

below the frequency marked on your transmitter. This is perfectly
normal. If you can’t hear the signal at all, try moving through the

whole range of numbers on the rightmost digit. For example, if your
transmitter is marked 216.025 you may end up tuning somewhere

between 216.022 and 216.028 (possibly even further away.)

The FM4000 Model has a

Switch

of which megahertz (MHz) band
you want to tune to. (For example,

each of the 216, 217, 218, and 219
MHz bands.)

the front panel. It turns off again by turning to the left with a
final click.

Tuning

The frequency is selected with the three numbered
switches (two switches in

the case of the FM100.)

which gives you a choice

The Fine Tune Knob

can adjust the frequency slightly (within one
KHz.) The tuning is very broad and not “touchy.”

When tracking an extremely weak signal this

knob is useful because you will get the best range by adjusting the
Fine Tune to the strongest pitch (about 700-800 Hertz, or the upper

end of the treble clef on a piano).
For everyday tracking you can set Fine Tune anywhere you want –

many people prefer very high tones because they are sound so
clear. Just tune to what sounds best to you.

Band

The FM1000

FM1000 gives 1000 different frequ ency

FM1000FM1000

choices.

The FM4000

FM 4000 gives 4000 different frequencies

FM 4000FM 4000

choices by providing a Band Selection Switch.

is available so you

G E T T I N G S T A R T E D

Page 7

Field Marshall Tracking Receiver

The

Range Switch

able to estimate the distance to the trans­mitter, a process called ranging. When

7

transmitter from a distance, the key question often
is, “when should I get out and start walking?” A
common mistake is getting out on foot too soon,

thinking you are near enough to walk. The

Medium

When the signal can be heard on Medium, you’re
close enough to get out and search on foot.

Note: Other receivers have powerful Medium settings which tend to fool
you into thinking a transmitter is closer than it is. This high sensitivity is
good on Far, but on Medium, this is not a virtue. The Field Marshall is

intentionally designed with a weaker, and more precise Medium range.

The
weak to be heard on Medium.

Comparing the range of two receivers set on Medium is like racing two
cars in only second gear — winning means nothing because the gear ratios

are arbitrary. Only compare performance of receivers with the ranges of
both receivers set to Far. To have a race, put them both in high gear.

G E T T I N G S T A R T E D

Solution: If the Receiver has lost directionality simply turn down the

Volume

you are driving in your vehicle toward the

setting helps you avoid this mistake.

Setting Action

Far Stay in car
Medium Start Walking

Near Look around you

Far

range setting is for use in all situations when the signal is too

, or switch to

Medium

is provided to be

The

Near

range setting is not
used in ordinary tracking. In
extreme situations it allows

you to accurately pinpoint a
transmitter which is very near
but hidden from sight.

As with any receiver, you want to avoid
overdriving it. This happens when you
turn up the

8

every direction, (sometimes the signal may
actually decrease in the direction of the

transmitter.)

doesn’t hurt the digital Field Marshall, but
makes it so you get the same signal in

or

Near

.

Volume

too far. Overdriving

Page 8

Owner’s Manual

Other Features . . .

Batteries

The digital Field Marshall uses six AAA

1.5 Volt batteries. You can use any name
brand Alkaline batteries, although more

expensive Lithium batteries can be used
for longer life. (Older style Zinc-Carbon

batteries are not recommended.) AAA
Lithium 1.5V batteries work better in cold
weather (below about -7º C (20º F).)

Actual battery life depends on many factors, including temperature and
how long it is used continuously. All batteries will run longer if used for

short periods of time with time to rest in between (rather than continuously
with no rest.)

Caution:

polarity as shown in the picture and

marked on the battery cover lid – negative
on the two sides and positive in the
middle.

The Low battery Light wil l begin to

come on when it is time to change

the batteries.

Please observe the battery

Energizer
Battery

Typical

Life

(hours)

AAA Alkaline 10.5 $.36
AAA Titanium 11.5 $.65
AAA Lithium 14.0 $1.07

Maintaining Directionality.

Avoid deflecting the Meter much more than full scale
(the Meter is not much use then anyway.) This can be

done by switching to Medium or Near or just turning
down the Volume.

Cost per

Hour

(USD)

Page 9

Field Marshall Tracking Receiver

External Power

The External Power Jack is available for

use with a standard 12 volt automotive

cigarette lighter adapter with a negative

ground. You can also use DC voltage

from any external source between 7.5

and 14 volts that can supply up to 200

mA.

Batteries in the receiver cannot be

recharged through the External Power

Jack.

Quick Release Handle

The handle can be conveniently removed
if desired by simply

turning the thumbwheel and
sliding the handle out.

Water

The Field Marshall is very water resistant, and the speakers are
completely waterproof. It should have no problem with an ordinary

rainstorm as long as you shield the Front Panel from the direct
spray of the rain. That said, the receiver is not warranted against

any water damage.

If water does get into the receiver (or if it has unusual behavior after

exposure to water):

First: Immediately turn off the re­ceiver and take the batteries out.

(Wet batteries may swell up and

become impossible to remove.)
Set the receiver on a flat surface

with the Front Panel tilted downward
so the water drains out the bottom

of the front. Don’t turn the receiver
back on until it is completely dry.

The “drying out” position

Page 10

Owner’s Manual

Headphones

in noisy environments and are strongly recommended for
serious tracking and listening to very weak signals.

give a big advantage when tracking weak signals

Page 11

Field Marshall Tracking Receiver

In The Field – A Quick Tutorial

Basic Tracking

The best way to become familiar with your receiver is to use it
outside. Turn on a transmitter and place it about 100 yards

away. Set the Range Switch to medium. Adjust the Tuning
Knob until you hear a clear beeping tone from the transmitter.

Adjust the volume to a comfortable level.

Hold the receiver in front of you at eye level with the elements
horizontal. Now, rotate your body 360°, keeping the receiver in

the same position. Can you hear the volume of the beep
change as you turn around? Was it strongest when you pointed

it at the transmitter? This is the basic technique of telemetry:
Scan the horizon with the antenna until you get the strongest

signal. That will generally be the direction that will take you to
the transmitter (that’s not always the case, though; see the next

chapter for more about this.)

Page 12

Owner’s Manual

Vertical vs. Horizontal

Now, point the receiver at the transmitter again and rotate the
antenna until the elements are vertical. Did the strength of the

signal change? Or was it strongest somewhere in-between? In
most cases, one orientation will be stronger than any other.

This is important: Make it a habit to rotate the receiver from
horizontal to vertical every time you use it at a new location.

Practice:

1. Have someone hide the transmitter in a difficult spot and see if
you can find it. You can make a game out of this. (Thousands of

ham radio enthusiasts actually conduct competitive transmitter
hunts in major cities in the US and around the world.) Or, put the
transmitter on a person, give them a head start, and see if you

can track them down.

2. Hang the transmitter with the antenna vertical on a wooden
object or a string and drive away with your receiver (don’t set it

on the ground, though; transmitters always perform poorly on the
ground.) See how far you can go before losing the signal. Try

tuning in the signal when it is very weak. Experiment with all the
controls and see what effect on the signal they have at a dis-

tance.

Page 13

Field Marshall Tracking Receiver

In the Field

When you’re ready to use the system in the field, tune in the
signal just before letting your bird or dog go. That ensures you’ll

be ready with the best signal instead of having to try to locate it
in the rush of the moment when the animal first becomes lost.

A few pointers on tuning:

• Set the numbers to match the frequency shown on the
transmitter. From there you might rotate the third num-

ber up or down to get the best signal.

• Tune the receiver for the loudest sound after the trans­mitter is on the animal and has reached the outside air

temperature. This is not necessary with Marshall trans­mitters but other brands can experience frequency drift

with changes in temperature.

• If you tune in while the transmitter is sitting next to you
on the car seat, the signal will be so powerful that your

receiver may pick it up on adjacent or incorrect

channels. If you mistakenly tune in on the wrong chan-

nel the signal may sound fine in the car, but will be
quickly lost when the transmitter is far away. To avoid

this, set the Range Switch on Near while tuning any­where near the transmitter.

Try locating your animal several times for practice. Experiment
with holding the receiver antenna vertically and horizontally

while watching the position of your animal. Use the system
many times until you feel confident in finding your animal with

telemetry. When your bird or dog is lost is not the time to be

learning how to use telemetry.

Page 14

Owner’s Manual

Page 15

Field Marshall Tracking Receiver

Frequently Asked Questions

Why does my receiver pick up all my transmitters at
the same time? They’re on different channels.

Extremely strong signals will get through even the most power­ful filters in a receiver. If you have transmitters on adjacent

channels transmitting right around you, you might hear a pop-
ping or thumping sound from them. This can be a distraction

when you’re trying to pick up a very weak signal from a lost ani­mal.

The solution is to turn off the transmitters around you while you
track a lost animal. If you’re just tuning up, switching the Range

Switch to Near will help to remove the unwanted signals.

I lost the signal and tried to tune it in. I couldn’t get it
again.

If you lose the signal, don’t panic and tune all over the dial. It’s
essential not to lose the correct tuning. The signal may have

drifted, but not much. So if you really think the signal could
have drifted, take note of the setting and then just turn the

Tuning Knob very slightly and search for the signal by scanning
the horizon 360º. If you don’t find it, you’re out of range. Turn

the Tuning Knob back where it was when you last heard the
signal and go to higher location and try again.

I could only pick up a transmitter a half a mile away.

This usually happens because the transmitter is putting out a
weak signal. The range of transmitters varies tremendously,

depending on where they are. A transmitter on the ground may
go less than half a mile. If the antenna is pointing directly at

you, you may hear almost nothing.
If the transmitter is putting out a good signal, the problem is

almost always improper tuning of the receiver. It’s possible to
tune to a tone that sounds like your transmitter, but is actually

at the wrong frequency (or even on the wrong channel!) It will
sound fine when you’re right next to the transmitter, but when

you get in the field it becomes weak (This can happen on any
receiver.)

Page 16

Owner’s Manual

To avoid this, set your receiver on Near when you tune up –
this removes all but the real, genuine signal you want to tune

to. And stand a short distance away when you tune up.

What is the single most important thing to do if I ab­solutely don’t want to lose my animal?

Put a backup transmitter on the animal. The second transmitter
can be a smaller one, or perhaps one with longer battery life (a

good combination would be one extremely powerful transmitter
that you can use the first few days, and another that lasts a

long time, in case you don’t find it right away.) Just remember
this: if your animal has a working transmitter, you can almost

always find it. It may take hiring a plane to fly over the area, but
eventually you can find it if you’re patient and there is a signal.

I’m not exactly certain what direction the transmitter
is. Am I doing something wrong?

Getting the sharpest bearing to your transmitter saves a lot of
searching (that’s why Marshall receivers use a full size, three

element yagi antenna). A three or five element yagi is more
precise, and a two element antenna is almost worthless. But

the following, easy technique can help you get a more accurate
bearing.

Instead of trying to find the strongest signal, try to find two
points on either side of it. Scan to both sides of the maximum

signal and notice the points on the horizon where the signal
drops exactly 1 unit on the S-Meter. Your best bet is that the

transmitter is halfway between those two points.
By the way, the wrong setting of the Range Switch could cause

this problem, too. See the following question.

Page 17

Field Marshall Tracking Receiver

Why is the Range Switch necessary? My other re­ceiver didn’t have one.

The Range Switch is a feature that allows you to get a rough
idea of the distance to the transmitter.

If the signal is very strong and you don’t switch down to Me-
dium or Near, the receiver will not point out the right direction

very precisely. The strong signal also saturates the receiver,
making all signals sound equally loud. This is common to all

receivers.

How can I tell how far away my transmitter is?

One of the biggest challenges in telemetry is determining dis­tance. There is no scientifically sound way of getting the dis-

tance from a transmitter signal. You can easily be deceived by
a loud signal from a transmitter very far away. However, there

are a couple of tricks to estimating it:

Page 18

Owner’s Manual

Distance Technique #1: Let’s assume you are receiv-

ing a strong signal with the Range Switch on Far. Now
flip the switch from Far to Medium. If the signal remains

strong, it means you are fairly close to the transmitter.
With a strong signal, here are typical ranges to a trans-

mitter near the ground:

Near ............................Less than 200 feet

Medium........................About 1/2 mile

Far...............................Over 1/2 mile

The above table is only an example; you won’t get the
same results. It depends on your transmitter, the ter-

rain, and many other factors. But over time you’ll get a
feel for the distance these Range settings represent

with your transmitter and terrain.

Distance Technique #2: Just take a reading on the S­Meter and then proceed in the direction of the transmit-

ter until the meter reads twice as much. You will have
covered approximately half the distance to your target.

This only works with direct line-of-sight signals of the
same polarization and gives only an approximation.

Still, it could save you from driving miles out of your
way. Adjust the Volume Knob during the first reading so

the meter reads about a third of full scale (where it is
likely to be the most linear.)

Page 19

Field Marshall Tracking Receiver

What is a KHz and a MHz?

These are measurements of frequency. Every transmitter has a
unique frequency that makes it distinguishable from all others.

Fortunately, a receiver can tune into a single frequency at a
time and reject all the others.

The basic measure of frequency is the hertz. It represents one
cycle or vibration per second. A kilohertz (kHz) is a thousand

cycles per second, and a megahertz (MHz) is a million cycles
per second.

An AM broadcast station is fairly in low in frequency, perhaps .7
MHz, while an FM station is much higher, say at 105 MHz. Your

telemetry operates at a still higher frequency, such as 216.055
MHz. Thus, a single short pulse from your transmitter is made

up of several tens of millions electro-magnetic vibrations.
The kilohertz unit is usually used in telemetry to measure the

difference between frequencies. For example, if you had a sec­ond transmitter at 216.070, it would be 15 kHz higher than the

one mentioned in the previous paragraph. .

Is there an easier way to get the receiver in and out of
the car.

It’s a lot easier if you push the sliding channel closed, partially
collapsing the antenna. However, don’t forget to extend it when

using the receiver in order to get maximum performance from
the antenna.

How can I use my Marshall receiver with my car top
antenna? It’s got a different plug.

Marshall receivers use high reliability, lightweight, gold-plated
SMB connectors. Call to order a short adapter that will fit the

larger BNC connectors used on some other antennas.

Page 20

Owner’s Manual

Page 21

Field Marshall Tracking Receiver

Page 22

Owner’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 an­tenna. 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:

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.

When your bird or dog is out of sight, the donut pattern can

Page 23

Field Marshall Tracking Receiver

Polarization

Radio waves are electromagnetic, exactly the same as light.
When your animal is lost you’re literally seeing it, with different

eyes. The miracle is that the transmitters used in telemetry emit
such small power, a few thousandths of a watt. Picking up that

tiny signal is equivalent to seeing a dim, blinking flashlight miles
away in daylight. Listening to your receiver is like looking

through a telescope: you can look but one direction at a time,
but your visibility is high.

You know from using sunglasses that sunlight is somewhat po­larized. Radio waves are strongly polarized. Polarization has to

do with the alignment of the magnetic and electric fields that
make up the wave. When the transmitter antenna is vertical we

say the waves are vertically polarized, and when it’s laying on
its side they are horizontally polarized.

The thing to remember is that your receiving antenna should be
oriented the same way as your transmitter antenna. This is im-

portant with weak signals. Your antenna will work poorly if it’s
oriented the wrong way, as much as ten times worse. The best

orientation could be somewhere between vertical and horizon­tal, maybe at 60º from horizontal.

Rule #1:

ing the orientation by 180 degrees. Stay with the orienta­tion that gives the strongest signal. This cannot be empha-

sized strongly enough. It is easy to develop a preference for
which way to hold your antenna, but in doing so you will miss

the boat half the time. Try them both and remember that your
target can change positions at any time.

The yagi antenna’s directionality is somewhat sharper if you
hold it horizontally, so you’ll want to use this orientation when-

ever you have a strong signal.
Radiation from the end of the transmitter antenna (around the

hole of the donut) has elements of both vertical and horizontal
polarization. And after a signal has been reflected it loses its

polarization altogether. The same loss of polarization can occur
after the wave travels through obstacles.

When tracking a weak signal, always try rotat-

Page 24

Owner’s Manual

Hint:

in a canyon and get a strong reading from a canyon wall. Either
your transmitter’s up there, or it’s a reflection off the canyon

wall from somewhere else. Before climbing, check the polarity
of the signal. If it’s a reflection the strength won’t change much

as you rotate the yagi around its axis.

Yagi Pattern

The Stealth Antenna is a form of directional antenna called a
yagi. It receives signals better in one direction than in others,

and that’s the only way you’ll find your animal when it’s out of
sight. Listening to the strength of the signal alone is almost use-

less, unless you have a lot of time to travel. You need a bear­ing. The yagi also has gain, picking up weak signals better as if

it were amplifying them. It can pick up a far away transmitter
when other antennas would get nothing.

A yagi can best be described by its radiation pattern. It always
has a distinct forward lobe in the favored direction. The width of

the forward lobe is its beamwidth, the range over which the
antenna picks up strong signals as you scan across the

horizon. A sharper beamwidth allows you to pinpoint the
direction to your animal more precisely, like a spotlight

compared to a floodlight.
Yagis also pick up signals in other directions besides forward.

The back and side lobes can confuse your ability to determine
the direction to your animal. The strength of the forward lobe

relative to the back is known as the front-to-back ratio, a higher
ratio being better.

Absence of polarization can be a clue. Suppose you’re

Page 25

Field Marshall Tracking Receiver

Rule #2:

scan the entire horizon first, all 360 degrees. Otherwise you
could find yourself following the back lobe, going exactly the

opposite direction from your animal.

The Field Marshall antenna provides the best combination of gain
and sharp pattern possible in a 3 element yagi. Your Marshall

receiver can be used with other antennas in addition to the built-in
Antenna. A car-mounted 5 or 7 element yagi is an excellent

antenna for long distance telemetry.

Whenever you take a new bearing with your yagi,

Omni-directional an­tennas

These antennas pick up
equally well in all directions.

You should use one in your
vehicle when moving to the

next point where you’ll take a
bearing. Hearing the signal

from your animal can tell you
if you’re going in the right di-

rection and warn you if you’re
about to lose the signal.

Yagi Tips

Don’t touch the elements while using it. Keep it away from other
objects, especially cars and other people. Don’t substitute other

lengths of coax. The gain of your antenna can change if you raise
it up or down, so keep it at a fixed height as you scan (higher is

generally better.)
In spite of the above guidelines, a yagi is very forgiving. It will

almost always guide you directly to your lost animal, hopefully
awaiting your appearance.

Page 26

Owner’s Manual

Hint:

take a bearing with your yagi. At least then you’ll know what
point of the horizon your animal just disappeared behind, a vital

piece of information.
The omni-directional antenna is also useful when you lose the

signal altogether. Hook it up and drive around in widening
circles around where you think the animal should be until you

hear something.
The most common omni-directional antenna is probably a

magnetically mounted whip (shown below). It should be in the
center of the vehicle roof, as the roof forms a key component of

the antenna. Whip antennas are usually 1/4 wavelength long.
A 5/8 wavelength whip is a little stronger in the horizontal

directions.
Be aware that the vertical whip is vertically polarized. That can

be a big disadvantage if your transmitter’s antenna is horizontal
and the signal is weak.

If the signal starts getting weak you know to stop and

Page 27

Field Marshall Tracking Receiver

Radio Wave Propagation

Radio waves normally travel in straight lines, but like light, they
can also play tricks. Unless you do your hunting on an utterly flat,

dry, treeless plain, you will experience all of the deceptions below:

Reflections

Radio waves reflect under many conditions and the result is
always an illusion. You think the transmitter is behind the point of

reflection, but it isn’t so.
Suppose, for example, you pick up the signal coming from the side

of a mountain. You spend hours climbing to the place only to find
no transmitter there. It never was there. What you saw was the

reflection of the transmitter’s signal from another valley. You’re
comforted by the fact that without a reflection you would have

no signal at all.
Radio waves reflect off any surfaces that conduct electricity, in-

cluding the following:

• Metal is the ideal reflector. Reflections from your nearby
vehicle can easily give you a false reading and the steel in a

building can scatter the signal in every direction.

• Water is another good conductor. Radio waves will bounce
off the surface of a lake like light off a reflecting pool.

• Hills and mountains reflect, but their properties will depend
on the nature of the material in them, particularly the mois-

ture they hold; wetter structures reflect better. Most natural
structures will give significant reflections.

• Live trees reflect radio waves, but dry wood does not. A
forest can scatter the signal in many directions. Any green

plant more than a meter in size can do it.

Radio reflections occur just like with a mirror, in that the angle the
wave comes out is the same as the angle going in. A flat surface

will reflect the signal in only one direction (the concept behind the
flat, angular surfaces of Stealth aircraft), while a rounded surface

will reflect in many directions, and most natural surfaces behave
like that. Multiple reflections are possible and a signal may funnel

a long distance down a canyon through successive reflections.

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Owner’s Manual

Fences & Wires

A fence picks up your transmitter’s signal, like an antenna, and the
signal races down the wire and re-radiates. Your receiver picks up

false signals which will most likely be horizontally polarized. The
effect is most pronounced when your target is right next to the

wire.

Checkerboard Patterns

When you are near the animal you may experience checkerboard
patterns (technically known as interference patterns.) If you plotted

the strength of the signal near your transmitter, it would look some­thing like a round checkerboard. One spot is strong, while a few

feet away you get little signal.
Checkerboard patterns occur when the signal reaches your re-

ceiver over two different paths, one being line-of-sight and the
other a reflection off the ground. When the two signals combine

they complement each other in certain spots, nullifying each other
in others.

When the transmitter is close: The checkerboard effect is
most pronounced when your animal is off the ground in a

tree, especially when the transmitter antenna is pointing at
you. Checkerboard patterns can weaken the signal in the

direction of the animal while it remains strong in some other
false direction. It can throw you off by exactly ninety degrees!

Don’t rely on signal strength alone to find the animal, espe­cially up close, because you could have just moved into one

of the low signal pockets. Instead, rely on the directionality
provided by your antenna. Don’t get too close. Circle where

you think the animal is. Use vertical polarization, since
ground doesn’t reflect vertical waves well.

When the transmitter is distant: The checkerboard effect
simply makes the signal stronger in some spots. Therefore,

when you’re trying to pick up a very weak signal, always

move around and try to get the signal at several spots within
a 15 foot radius.

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Field Marshall Tracking Receiver

Terrain Absorption

As radio waves pass through objects they diminish in strength. The
effect is most noticeable in wooded areas where vegetation saps

the strength of your signal. The further it goes through a forest the
greater the loss. Fog, clouds, snow and rain also absorb radio

waves, lowering your transmitter’s range. Your Marshall system,
between 173 and 220 mHz, avoids the absorption problems that

are more pronounced at higher frequencies.

Radio Shadows

The biggest obstacle to radio waves is the earth itself. The range of
a telemetry system is limited first and foremost by the horizon. The

curvature of the earth creates a circular area around the transmitter
where you can pick up the signal, the so-called line-of-sight radius.

The actual radius depends on the elevation of both the transmitter
and the receiver.

what it would be if the earth were smooth. Every kind of terrain pro­duces “radio shadows”. As you move around you can go in and out

of shadows, even picking up a signal much further away from a
spot where you picked up no signal.

This diagram can give you
an idea of the line-of-sight

distance. To use it compute
the distance for the height

of the transmitter and your
own height separately, then

add them together. For
example, if your transmitter

was on a hill 25 feet high
and your receiver was 8

feet high, the line-of-site
distance would be 11 miles

(7 + 4 miles).
You can see that if your

transmitter is on flat ground
and you are standing on the

ground, the range can be
just a few miles. Irregulari-

ties like hills reduce the line

-of-sight to even less than

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Owner’s Manual

The key to getting the best range from your receiver is altitude.
High spots are least likely to be in a shadow. If you’re not

getting a good signal, the first thing to do is get higher. Driving
to the top of a hill or climbing a water tower can dramatically

increase your transmitter’s range.

Hint:

When tracking a

weak signal, hold your
antenna as high as you

can reach instead of
keeping it at eye level.

Standing on your
vehicle will also boost

the signal significantly.

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Field Marshall Tracking Receiver

Diffraction

Fortunately, radio waves can bend around objects. Diffraction
works best around metal edges in buildings, but also happens

with hills, trees and mountains. Diffraction increases the range
of your transmitter beyond line-of-sight, because the signal

bends over the crest of the hills.
This means your transmitter’s range is not determined strictly

by the above line-of-sight chart. Diffraction allows some of the
signal to “hug the earth” and go further than the strict horizon,

tapering off gradually as you go beyond it. A transmitter beyond
a hill or in a deep ravine would be undetectable if it weren’t for

diffraction around the edges. A powerful transmitter can use
diffraction to punch a signal beyond the line-of-site limit.

Diffraction around trees combined with reflections can create
complex patterns within the forest. You should hold your

antenna horizontally in a forest because trees produce mostly
vertical interference.

It is important to remember that the frequency is very important.
Higher frequency means less diffraction. Higher frequency

transmitters may perform equally well at close range on flat
ground, but will not do well at a distance or in hilly terrain. This

is unfortunate, because higher frequencies allow smaller
antennas. The frequency of your Marshall receiver, between

173 and 220 MHz gives a good compromise between antenna
size and ground-hugging (diffraction) ability.

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Owner’s Manual

Tracking Strategies

The Marshall receivers and transmitters are the finest available
to telemetry users. While good equipment helps, good

technique is equally important when your animal is really lost.
Most of the time you’ll find it absolutely no problem, but there

are those times when you’ll want every advantage possible.
Here are some techniques that can help:

Before starting

Always check your transmitters for a strong antenna connection
and for any kind of corrosion on the battery contacts. Check

your transmitter’s battery or use a new one. The battery is the
most likely component in your system to fail. Also, test your

receiver batteries and have spares ready. Turn on the
transmitters and attach to the animals. Select the channel of

each transmitter and adjust the tuning for the optimal (loudest)
sound.

The Initial Bearing

When you first lose the animal, use your receiver immediately
to acquire the signal. You may not be able to run back to the

vehicle; the receiver should be with you and ready. Try to
determine the animal’s direction through your last visual contact

and by considering its past behavior. A strong signal indicates
you have line-of-sight conditions. A sudden weakening of the

signal indicates the animal has just gone over a hill.
Whatever you do, don’t lose the signal. While driving use an

omni-directional antenna on your vehicle roof. Stop frequently
to take new bearings, depending on how far away the animal is

and on your confidence in your estimating its direction and
speed. Your goal is to keep within range of the animal until you

have an indication it has halted, through the activity sensor on
the transmitter or the lack of change in the signal.

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Field Marshall Tracking Receiver

Each time you take a bearing always scan a full 360°radius first to
find the peak response. Remember that every yagi has a certain

response 180° from the peak and if you’re not careful you could go
in exactly the wrong direction. To get the most precise bearing,

turn the volume down so you get no signal except on the peak.
If the signal is weak, rotate the yagi around it’s boom to find the

best polarization, vertical or horizontal. If both polarizations are
about equal, the signal could be coming from a reflection off a hill

or mountain or could be diffracting over a hill. If you suspect you
have a reflection, try to figure out where the transmitter would be if

it is in the direction of the bounce (remember that radio waves
reflect off a surface exactly the way light waves do in a mirror; the

incoming angle equals the outgoing angle.) Check for a weaker
signal coming from the true direction to the transmitter masked by

some obstacle.
As you move the yagi across the horizon, is the peak response

sharp or broad? A broad response may indicate a reflection or
diffraction over an obstacle. As you drive away does the signal

drop off rapidly? This may indicate the transmitter is low or is
behind an obstruction rather than high.

Note whether there are any buildings, wires or fences in the
vicinity, or other obvious objects the signal could be reflecting

from. The signal can travel many miles along wires. Also
remember the signal intensity on your Meter for comparison with

the next reading you take.

Triangulation

After you take your first bearing, the natural tendency is to go
straight in that direction toward the transmitter. And if you have a

pretty good idea where the transmitter is that’s not a bad idea.
However, usually you will end up taking a lot of extra

measurements that way because you lack information about the
transmitter’s distance. If the signal is weak it doesn’t always mean

the transmitter is far away.
Another approach is triangulation. Instead of moving directly to-

ward where you think the transmitter is, you move closer and side­ways. By taking only two bearings you can theoretically pinpoint

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Owner’s Manual

the exact location of the transmitter: at the intersection of the two
lines. You probably can’t follow the line to the transmitter directly

anyway because of roads and obstacles or the need to stay on
high ground, so take advantage of that fact.

For triangulation to work, you have to remember the line of the
previous bearing. You can do that mentally by noting two land-

marks on that line as you take the bearing. Note a landmark
behind the transmitter and another behind you. When you take the

next bearing you’ll know that the transmitter should be somewhere
on the line connecting the two landmarks. Proceed toward the

point of intersection, but again offset to a third point. You’ll end up
rapidly closing in on the transmitter in a spiral.

If you lose the signal altogether:

Go to high ground. If that doesn’t help try high ground on the other
side of where you expect the transmitter to be or that looks over

the horizon in the direction the animal was headed. If you have no
clue where the animal is, drive in widening concentric circles

around where you last saw it, as closely as roads will permit. If you
have an omni-directional antenna put it on and keep your receiver

on.
When you are on a hilltop, the best location for getting a weak sig-

nal is usually slightly in front of the peak, though you can get a
better 360°radius from the top.

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Field Marshall Tracking Receiver

The ultimate way to get up high is to hire an airplane and circle
the area, using a yagi antenna mounted on the wing struts,

pointing at an angle downward. Be sure to use good head­phones in a plane. You’ll need a long piece of antenna coax

with the right connectors on each end.

Getting Hot

When you’re close to the transmitter, it’s tempting to rush in to
find the bird or dog. However, you will do well to keep taking

frequent bearings to avoid overshooting its location. You may
have come to this spot based on a reflection while the main

signal was obscured by an obstacle. Once you’re past the
obstacle the real signal may actually be behind you. So

continue to take 360° readings as you proceed closer.
Before setting out on foot, make sure you’re within walking

distance. You’ll waste a lot of time if you leave your vehicle
prematurely. Triangulation will give you a good clue how close

you are, or you can use the Meter technique described above.
Reduce your receiver volume and switch to Medium or Near

range as you get close. Don’t remove your antenna as you may
do with other receivers. The Field Marshall Receiver has

exceptional shielding that maintains sharp directionality even
when you walk to without a few feet of the transmitter.

Continue triangulating, circling around the apparent location at
a distance and taking multiple bearings. Then just walk to

where they all intersect. Look out for reflections from fences
and other metal objects, which will be much stronger when

you’re close to the transmitter. If the transmitter antenna
happens to be pointing at you you’ll get the weakest signal

while the strong broadside radiation may reflect off nearby
objects giving much stronger signals in those directions.

Page 36

Owner’s Manual

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Field Marshall Tracking Receiver

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Owner’s Manual

Warranty

Marshall Radio Telemetry warrants that its receivers will be free from defects of workmanship
and materials for THREE YEARS from date of purchase. If your receiver is defective return it
to your distributor and we will repair or replace it and return it free of charge. However, we will
not be responsible for damage from misuse or normal damage incurred during use. Under no

circumstances will Marshall Radio be responsible for damages or loss beyond the value of the
receiver itself, including the loss of an animal or lost time. The complete unit must be re-

turned, transportation prepaid, to a Marshall Radio authorized Service Center.

Service

If something is wrong with your receiver, whether under warranty or otherwise, please do the
following:

In the USA and Canada:

Call 800-729-7123 and talk to Marshall Radio Telemetry’s Customer Service depart­ment. We will first try to determine the nature of the problem over the telephone and, if
necessary, give you instructions on how to return the unit for repair. Do not return
products without calling first.

In Europe:

Call the Marshall Direct office in the UK at (44) 161-870-6518. We will first try to deter­mine the nature of the problem over the telephone and, if necessary, give you instruc­tions on how to return the unit for repair. Do not return products without calling first.

Worldwide:

Contact your local distributor, or Call [phone]-9000 and talk to Marshall Radio
Telemetry’s Customer Service department. We will first try to determine the nature of
the problem over the telephone and, if necessary, give you instructions on how to

return the unit for repair. Do not return products without calling first.

Page 39

Field Marshall Tracking Receiver

Page 40

[phone]
[phone]

www.marshallradio.com