Ramsey Electronics COM 3 User manual

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©

COM
3
Service
Monitor
Owner's
Manual
Version
1.7
©
1987
Copyright
1987
by
Ramsey
Electronics
Inc.No
Part
of
this
publication
may
be
duplicated
in
part
or
whole
without
written
permission
by
an
officer
of
Ramsey
Electronics
Inc.

Section 1 -
CONTENTS
General Information
Introduction
Specifications
Options
Special Modifications
Installation
Introduction
Unpacking and Inspection
Power Requirements
Enviromental Considerations
Operation
Introduction
Front Panel Description
Initial Turn On
Generate RF
RF Output Level
FM Modulation
AM Modulation
CTS Tone Generation
1 KHz Internal Tone
External Source Input
Combining CTS and Internal/External
Tone Sources
Offset+ / Offset-
500 Hz Step
Storing/Recalling Test Setups
Spurious Signals
Leakage
Audio Count Off Air
Audio Count External
RF Count
Typical Test Setups
Introduction
Frequency Counter : Off Air
Frequency Counter : Direct Connection
Frequency / Deviation Measurements
20 dB Quieting Measurement
12dB Sinad Measurement

Loa AZ ሩሕ ALEKS ont ህጊ. 441
— A រត:
5.22
5.23
Section
6
-
General
512-1018
MHz
Coarse
Loop
PLL
5-7
MHz
Fine
LoopPLL
.
1024
MHz
Offset
PLL
Output
Step
Attenuator
4
MHz
Reference
Standard
FM
Modulator
AM
Modulator
1
KHz
Source
Receiver
16
KHz
Reference
Generator
Frequency
Error
Detector
Audio Amp
+30
Volt
and-10
Volt
Supplies
Transmit
Protection
Circuit
DC
Supply
and
Battery
Membrane
Switch
Microprocessor
E
Display
Drivers
Audio
Frequency
Counter
RF
Frequency
Counter
CTS
Tone
Generation
Frequency
Error/Deviation
Display
Documents,
Figures
Fig
3.1
Front
panel
layout
Fig
4.1
Block
diagram
Schematic
diagram
Warranty
Test data

ON 1
SECTI
GENERAL
INFORMATION
The
Com
3
is
a
lightweight,
compact
Service
monitor
for
testing
AM
and
FM
transceivers.
The
internal
battery,
which
is
a
standard
feature
of
the
Com
3,
combin
ed
with
the
optional
carrying
case
and
low
weight
(13
lbs),
make
it
ideal
for
field
use.
Utilizing
specially
designed
micro
Powered
oven
circuits,
warm
-up
time
is
minimal,
providing
maximum
use
of
the
battery.
tone
can
be
generated.
RF
power
is
continu
variable
in
five
ranges
from
0.1
uv
to
10,000
uv.
The
display
is
a
seven
digit
LED
type
which
will
display
frequenci
i
i
audio
ahd
RF
frequency
counter.
Deviation
and
frequency
error
are
displayed
on
a
20
segment
LED
bargraph,
which
is
easily
visible
from
across
the
shop.
|
An
internal
RF
relay
switches
transmitted
power
greater
than
500
mW
to
a
rear
panel
mounted
BNC
connector.
This
protects
the
Com
3
from
accidental
keying
and
allows
easy
connection
of
an
antenna,
power
meter,
or
dummy
load.
1-1

1.2
Specifications
1.21
Generate
Mode
1.2.1.1
Frequency
Range
Resolution
Display
Accuracy
1.2.1.2
Rf
Output
Range
Accuracy
Attenuctor
1.2.1.3
Spectral
Purity
Non-Harmonic
Other
1.2.1.4
Reverse
Power
Protection
Type
Power
1.2.1.5
Modulawion
Deviation
Ranges
100
KHz
to
999.999
MHz
500
Hz
7
digit
LED
see time base
0.1
uv
to
10,0000
uv
ind
ranges
+2.0
dB
(10
MHz
to
900
MHz)
20 dB/step
«-50
dBc
within
10
KHz
of
carrier
(all
land
mobile
bands)
2
signals,
f1
and
f2
Forf1
=
(fc
+
Fine
Loop)
10
dB
below
maximum
RF
output
range
selected
Forf2
=
(fc
+
2(
Fine
Loop)
MHz,
same
level
as
fc
Fine
Loop:
5
to
7
MHz,
depending
upon
selected
frequency
Automatically
switches
to
external
load
at
inputs
. >500 mw
Up
to
100
watts
(10
seconds)
FM
0
to
15
KHz
peak
(displays
to
7
KHz
only)
41.5, +7.0 KHz
NIME

1.2.2.2
Bandwidth,3dB
Accuracy
External Input
Depth
Bandwith, 3dB
Accuracy at 30 % mod.
External Input
Receive Mode
Frequency
Range
Resolution
Display
Accuracy
Sensitivity
Bandwidth
Modulation Measurement Mode
FM Mode
Deviation
Ranges
Bandwidth, 3 dB
Accuracy
Display
10 Hzto 10KHz
15% of full scale (1 KHz frequency)
1 vpp for 3 KHz peak |
AM |
0to 99%
10 Hz to 10 KHz
+5% of full scale (1 KHz frequency )
1 vpp for50%
100 KHz to 999.9999 MHz
500 Hz NS
7 digit LED
see time base
5.0
uv
for
10
dB
quieting
(10
MHz
to
900
MHz)
3dB/7KHz
Oto 7 KHz
+1.5, 2 7.0 KHz
10
Hz
to
10
KHz
(display
limited
to
<
7
KHz)
15% of full scale (1 KHz frequency )
20 segment LED bargraph

AM Mode
Ranges
Accuracy
Display
1.2.3
Time Base
Characteristics
STANDARD OCXO
Accuracy + 1.0ppm
Aging rate t 2.5ppm/year
Oper. range 01050?
Stability t 1.0 ppm after
5 minutes at 25 °C
1.25 Frequency Counter Mode
Ranges
1.2.6 GENERAL
Operating temperature
Power requirements
Dimensions
Weight
1.2.7 OPTIONS
High stability timebase
12 VDC cigarette plug
Cordura travel case
Protective front cover
Side Handle
(Carrier frequency error only)
+1.5,+ 7.0 KHz
+5% of full scale
20 segment LED bargraph
HIGH
STABILITY
OCXO
+0.5
ppm,
+
0.25
ppm,
or
0.10
ppm
t
1.0
ppm/
year
01050^ C
ቷ 0.5 ppm after
10 minutes at 25 9 C
10
Hzto
1.0
KHz,
0.1
Hz
resolution
10
MHz
to
999.999 MHz, 1 KHz resolution
0to50?C
117 VAC, or12 VDC
12"Wx5.5"Hx14"D
13 Ibs
An oven controlled oscillator which increases the
accuracy to 0.5 ppm, 0.25 ppm, or 0.10 ppm
depending on which model is selected.
Allows
the
Com3
to
operate
from
a
car's
battery
A
rugged
carrying
case
made
from
black
Cordura
nylon,
with
a
convenient
zipper
pouch
for
holding schematics, probes etc.
Vacuum
formed
plastic
cover
for
protecting
the
Com
3's
front
panel.
Aside
mounted
handle
for
easy
transportation
of
the
Com
3.

1.28
SPECIAL
MODIFICATIONS
Due
to
the
constant
advancements
in
the
two
way
communications
field,
customer
needs
may
require
a
special
modification,
either
at
the
time
of
purchase,
or
some
time
in
the
future.
Contact
the
customer
service
department
at
716-586-3950.
We
will
do
our
best
to
meet
your
needs,
please
note
that
modifications
will
require
a
service
charge,
and
some
may
not
be
possible.

.
2.1
INTRODUCTION
The
Com
3
is
a
rugged,
portable
service
monitor
that
is
equally
at
home
in
the
field
or
on
the
bench.
Refer
to
the
following
sections
when
unpacking
your
service
monitor.
2.2
UNPACKING
AND
INSPECTION
When
unpacking
your
service
monitor
check,
the
shipping
container
and
the
monitor
for
shipping
damage.
Save
the
container
for
future
*
use,
orinthe
event
of
an
insurance
claim.
Your
Com
3
was
thoroughly
tested
and
inspected
,
then
carefully
packaged
prior
to
shipment
and
should
operate
according
to
section
3
of
this
manual.
|
If
your
monitor
was
damage
in
transit,
contact
the
carrier
immediately.
Save
all
shipping
and
packing
materials
for
inspection
by
the
carrier.
Contactthe
carrierto
reportthe
incident.
'
SECTION
2
INSTALLATION
5.3
POWER
REQUIREMENTS
The
Com
3
operates
on
117
VAC
60
HZ.
The
three
conductor
power
cord
provides
a
ground
connection
when
it
is
connected
to
a
properly
grounded
outlet.
Using
the
optional
12
VDC
power
cord,
the
Com
3
can
be
operated
from
a
Car's
battery.
The
Com
3's
internal
battery
cannot
be
charged
from
an
external
DC
source.
NOTE:
Do
not
start
the
engine
while
the
Com
3
is
plugged
into
the
cigarette
lighter.
This
could
result
in
damage
to
the
Com
3.
A
240
VAC
50
Hz
version
of
the
unit
is
available
by
special
order.
There
is
an
addtional
charge
for
this
option.
2.4
ENVIRONMENTAL
CONSIDERATIONS
The
Com
3
comes
equipped
with
bottom
and
rear
panel
feet
(
the
rear
panel
feet
act
as
cord
wraps),
and
a
tilt
bail
.
These
features
allow
the
unit
to
be
used
in
almost
any
situation.
The
Com
3
is
designed
to
operate
`
between
0°
C
and
50?
C.
Care
should
be
taken
to
keep
the
unit
clean
and
dry.
MEM
M

3.1 INTRODUCTION
Use of the Com 3 is as straight forward as the
front panel layout, you can begin using the Com
3 without even reading this manual. We suggest
you do read it though, to take advantage of all
the features available.
3.2 FRONT PANEL DESCRIPTION
The Com 3's front panel is a flat, fully sealed
membrane switch designed for years of reliable
service. All numeric data is entered through the
keypad located on the right front side. An
audible tone will sound when a key is
depressed to indicate positive contact.
Note, related keys that control the various
functions of the Com 3 are logically grouped ㆍ
together. Refer to figure 3.1 and the following
section for an explanation of each control and its
function.
SECTION 3
OPERATION
(1) POWER: applies AC power when the Com
3 is plugged into 8 standard 117 VAC outlet, or
supplies 12 VDC from the internal battery in areas
where there is no 117 VAC source available.
(2) LOW BAT: indicator lights when the internal
battery needs recharging.
(3) VOLUME: controls the audio level of the
~ internal speaker.
(4) DISPLAY: A 0.4" 7 segment LED display
shows the generate or receive frequency, AF
frequency, or RF count frequency depending on
mode selected.
Note; that the display is calibrated in KHz for the
Count AF mode and in MHz for all other modes.
(5) GENERATE RF: selects the GENERATE
RF mode. The display will indicate the frequency
being generated.

(6) COUNT RF: enables the Com 3's RF
frequency counter. The display wil show the
frequency being measured. Display indicates in
MHz.
(7) COUNT AF: enables the Com 3's audio
frequency counter, the display indicates in KHz.
(8) MONITOR FM: enables the monitor FM
mode, the display indicates the frequency
selected for monitoring.
(9) MONITOR AM: enables the monitor
AM mode, the display indicates the frequency
selected for monitoring.
(10) EM: enables the FM modulation mode.
Only operates inthe GENERATE RF mode.
(11) AM: enables the AM modulation mode.
Only operates inthe GENERATE RF mode.
(12) CTS: enables the CTS mode Generates
all standard EIA CTS tones from 50 Hz to 300 Hz
(see table 3.1) Only operates in the GENERATE
RF mode. |
(13) i KHz: enables the internal 1 KHz tone
source. Only operates in the GENERATE RF
mode.
(14) EXTERNAL: allows an external
modulation source to be connected to the Com 3's
external input. Signal can be looped through using
the IN and OUT jacks (numbers 15 and 16
respectively). Only operates in the GENERATE
RF mode. -
(15) ከህ: jack is for the input of an external |
modulation source. Approximately 1v p-p required
for 3 KHz deviation.
(16) | QUT: jack allows the external source to be
looped through the Com 3. Also will source CTS
and 1 KHz if so selected.
(17) MODULATION KNOB: controls the
percent modulation in AM mode,and the deviation
in FM mode. In the FM mode,the bargraph will
indicate the amount of FM deviation.
(18 BAR GRAPH DISPLAY: a 20 segment
LED bar graph display which shows deviation in
one mode and frequency error inthe other mode.
(19) FREQUENCY: sets the bargraph into
frequency error mode, touching the key again
changes the frequency range. 2 LED's light up,
one on each side of the range selected. l
(20) DEVIATION: sets the bargraph into
deviation mode, touching the key again will
change the deviation range. 2 LED's light up, one
on each side of the range selected.
(21) LEVEL UP: increases the output level in
1 dB. steps.
(22 LEVEL DOWN: reduces the output level
in 1 dB. steps.
(23) ATTENUATOR DISPLAY: indicates the
attenuator range selected.
(24) MICROVOLTS: control knob varies the -
output within the range selected.
(25) MONITOR AF OUT: jack allows deviation
to be rnonitored by using an oscilloscope.
(26) RF OUT: output jack thru which the
generate RF signal is available, and also the input
for a transmitter,
(27) RF IN: input jack for the Com 3's RF
frequency counter and Frequency / Deviation
receive monitor.
WARNING : Do not connect a transmitter to this
jack or serious damage will result!
(28)
Q-9:
used
for
numeric
data
entry
into
the
Com3.
(29) [፲1.., ihe Com 3 in 500 HZ-
increments up or down. Useful for checking a
receiver's discriminator zeroing.

(30) +OFFSET/-OFFSET: programmable offset
keys for repeater service, or channel stepping.
(31) CLR: clears the current entry in the display
(32) RCL: recalls a previously stored test setup.
(33) STO: stores the currenttest setup into one
of the Com3's ten memories ( 0 - 9).
3.3 INITIAL TURN ON
Connect the rear panel AC line cord to a
suitable power outlet and turn the power switch
on. The front panel display will light indicating
power on. When first turned on The Com 3
should always start out with these settings.
Display : 450.0000 MHz
Generate RF: on
FM: on
1 KHz: on CTS: off Ext.tone: off
Deviation: on, 1.5 Khz range selected
X10K: on
If these conditions do not exist refer to the
trouble shooting section.
Com 3's equipped with the standard OCXO will
generate _ 10001 precision signals — within10
minutes, Units equipped with the high stability
XO will produ .5ppm accur after 1
minutes. When using the Com 3 in cold
environments longer warm-up times may be
required.
DETAILED OPERATION OF THE COM 3
3.4 GENERATE RF
To generate an RF frequency, type in the
desired frequency then touch the GENERATE
RF
key.
NOTE:
the
display
always
reads
the
frequency in Mhz, therefore an entry of 10 would
generate 10 Mhz, an entry of 0.1 would
generate
100Khz.
For
frequencies
above
100
MHz,
it
is
not
necessary
to
enter
the
decimal
point.
3.5 RF OUTPUT LEVEL
The output level is controlled by a five step
attenuator and a variable attenuator. The ranges
available are; K
0.110 1.0ጩ/ ,1.0 to 10.0 nv ,10.0 to 100ፌሃ.
100 to1,000 ዚዜሃ,1,0001510,000 pv.
To select the desired range, touch the LEVEL UP
or LEVEL DOWN key to select the desired range.
An LED will light next to the range selected. The
output can be controlled within the range by the
control knob labeled MICROVOLTS.
3.6 FM MODULATION
To FM modulate the RF frequency selected, touch
the FM key. The deviation is adjustable by the
MODULATION: control knob. The indications on
the knob have no reference to the FM deviation,
they are used for AM. modulation. The deviation will
be displayed automatically on the LED bargraph.
3.7 AM MODULATION
To AM modulate the RF frequency selected, touch
the AM key. The percentage of modulation is
adjustable by the MODULATION control knob and
is variable from 10 to 100 percent.
3.6 CTS TONE GENERATION
The
Com3
will
generate
all
the
standard
CTS
tones
(see
table
3.1).
CTS
can
be
generated
in
either
the
AM
or
FM
modulation
modes,
and
in
conjunction
with
`
the
internal
1Khz
tone
source,
or
an
external
tone
source.
To
generate
a
CTS
tone
touch
the
CTS
key,
enter
the
desired
frequency,
then
press
the
CTS
key
again.
The
display
will
show
the
current
CTS
tone
being
generated.Power
up
default
tone
is
(100.0
Hz).
If
an
improper
tone
is
entered,
it
will
not
be
accepted.
To
return
the
display
to
the
generated
RF
display,
just
touch
the
GENERATE
RF
key,
to
display
the
CTS
tone
touch
the
CTS
key.
The
MODULATION
knob
will
control
the
deviation
of
the
CTS
tone
when
inthe
CTS
mode.

STANDARD EIA CTS TONES (Hz)
Table 3.1
3.9 1 KHz INTERNAL TONE
Touching the 1 KHz key will enable the
internal 1 KHz tone. In AM mode, the
MODULATION knob will control the percent
modulation, in FM mode it will control the
deviation.
3.10 EXTERNAL SOURCE INPUT
Touching the EXTERNAL key will allow the
connection of an external tone source. (see
specifications Chapter 1 for limitations on this ' -
input) The source is looped through the Com 3
using the IN and OUT jacks located under the
EXTERNAL key. The percentage of modulation
in AM mode is adjusted using the
MODULATION knob, in FM mode it will control
the deviation.
«9.31 COMBINING CTS AND INTERNAL /
EXTERNAL TONE SOURCES
.. Select the CTS frequency desired and
adjust for the desired deviation (for example 0.6
KHz). Then select the 1 KHz mode. The 1 KHz
tone will now have a deviation of 3 KHz, and will
vary in a 5/1 ratio with the CTS tone. (0.6 KHz
CTS deviation will produce 3 KHz deviation of
the 1 KHz tone).This ratio was chosen since the
most common deviation for CTS is 0.6 KHz and 3
KHz for voice. Having the two signals in this ratio
allows for CTS testing in the presence of voice.
Use of the CTS and EXTERNAL tone
sources work in a similiar manner as the CTS and
1 kHz. The CTS tone sets the same 5/1 ratio as in
the above example. An external input of 1 vp-p will
produce 3 KHz of deviation. Therefore a setting of
0.6 KHz CTS, with 1 vp-p external input will produce
3 KHz of deviation of the external tone.
3.12 OFFSET +/ OFFSET -
The Com 3 allows you to select any offset
frequency you desire. Enter in the desired offset
using the keyboard, then touch the STO key and
then touch the OFFSET+ key. This will store the
desired offset into the Com 3's memory. ‘Pressing
OFFSET+ or OFFSET- will increment or decrement
the display by the offset amount.
3.13 500Hz STEP
The two arrow keys are the 500Hz up or
down keys. Touching either of these keys will allow
you to step 500Hz at atime.
3.14 STORING/RECALLING TEST SETUPS
The Com 3 has the capability of storing up to 10
different test setups in its memory. Stored is the
current set-up selected on the Com 3's front panel,
including all frequencies being generated, CTS,
‘Offsets, etc. To store a test setup touch the STO
' key, then the number of where you want it stored
(0-9). To recall a setup, touch CLR, then RCL,
then the number of the memory you wish to recall
(0-9). |
3.15 SPURIOUS SIGNALS
in any wideband, receiver spurious signals
sometimes present problems. We would like to bring
to your attention the existance of a non-problematic
spur within the Com 3.
Refer to the block diagram. fig. 4.1) and the main
/ board schematic during the following explanation.
The Com 3 has a reference oscillator of 4 Mhz, the
fourth harmonic of this is 16 MHz. The first IF is from
14.5 to 16.5 MHz, and the second IF is 9.5 MHZ. As
you can see, if an incoming signal is at such a
frequency as to hit the first IF at 16 MHz, there
would be a possibility of interference or a
heterodyne due to the Com 3 receiving the forth
harmonic of its own reference oscillator. This will

occur every 1 MHz throughout the range of the
Com 3, for example, 450.0000,451.0000,
452.0000, 453.0000 etc. This does not present
a problem however, as the level of the fourth
harmonic is only approximately 10 uv. An
incoming signal of 20-30 uv will easily over come
this. ሸ you have selected a frequency under
these conditions please be aware that the
squelch will open up and a weak carrier will be
heard. This should be of no concern and is
considered normal.
3.16 Leakage
Leakage from the Com 3 is virtually
unmeasurable.
If
you
are
using
the
Com
3
witha
coax cable connecting your transceiver to the
RF OUT jack, you will probably never have to be
concerned wiih leakage.Most mobile and base
tranceivers have plenty of shielding in their front
ends,
they
will
not
normally
receive
any
minute
radiated
emissions.
However,
in
the
event
that
you
are
making
a
sensitivity
measurement
ona
handheld
unit
or
a
pager
utilizing
a
direct
cable
connection,
shielding
caps
should
be
placed
on
all
unused
connectors
and
the
test
set-up
should
be
positioned
away
from
the
com
3.
Handheld
units
and
pagers
are
designed
to
pick
up
radiated
emissions
directly
through
antennas
mounted
either
on
them
or
in
them,thus
they
have
little
use
for
expensive
front
end
shielding.True
ㆍ
radiated
emission
—
(uv/cm")
testing
of
a
pager
or
a
handheld
tranceiver
can
only
be
accomplished
using
an
RF
shielded
test
box
.This
is
especially
true
in
RF
congested
areas.Keep
in
mind
that
all
generators
even
the
most
expensive
models
radiate
some
amount
of
RF
especially
at
UHF.
You
may
be
able
to
sniff
out
some
RF
from
your
(6010
using
a
handheld
“
Or
a
pager
but
this
is
normal.
RF
shielded
boxes
and
rooms
are
widely
available
although
expensive.
3.17 Audio Count Off Air
To
measure
audio
frequencies
off
the
air,
set
the
Com
3
up
for
receive
on
the
channel
frequency
desired,
then
touch
the
COUNT
AF
key.
Select
the
approximate
deviation
range
of
the
tone
by
touching
the
DEVIATION
key
(
ranges
are
+
1.5,
+
7.0
KHz).
High
deviation
tones,
21.5
KHz
or
greater,
should
be
read
in
while
in
the
+
7
KHz
range,
while
low
deviation
tones,
such
as
CTS,
in
the
+
1.5
KHz
range.
The
display
will
now
indicate
the
audio
frequency.
8.18 Audio Count External
Connect
the
audio
source
to
the
external
IN
jack,
then
touch
the
GENERATE
RF
key
and
the
COUNTAF
key
in
that
order.
The
external
light
will
automatically
come
on,
and
the
display
will
indicate
the
audio
frequency.
The
input
level
must
be
at
least
50
mv,
but
should
not
exceed
5
v.
3.19 RF Count
To
count
RF
frequencies
connect
the
whip
antenna
to
the
RF
IN
jack,
then
touch
the
COUNT
RF
key,
the
display
will
indicate
the
frequency
in
-
MHz.
The
range
is
10
MHz
to
999.999
MHz,
resolution is 1 KHz.
WARNING:
Do
not
transmit
into
the
RF
IN
jack,
this
will
cause
serious
damage
to
your
Com
3.
This
jack
is
for
whip
antenna
connections
only.
Transceivérs
should
be
connected
to
the
RF
OUT
jack,
inputs
over500
mW
will
be
switched
to
the
rear
panel
mounted
BNC
connector.

41. INTRODUCTION
This
chapter
outlines
typical
measurements.that
can
be
made
with
the
Com
3.
For
our
example
we
will
use
a.FM
transceiver
with
a
receive
frequency
of
469.150
MHz,
a
transmit
frequency
of
464.150
MHz,
with
a
CTS
tone
of
82.5
Hz.
.NOTE
The
COM
3
DOES
NOT
have
an
enter
key.
After
entering
in
the
desired
frequency
a
function
must
be
selected
to
complete
the
entry,
or
nothing
will
happen.
(ie
enter
in
464.150
then
touch
the
GENERATE
FM
key)
The
function
keys
are
(GENERATE-FM
,
MONITOR-FM
and,
MONITOR-AM).
If
you
change
the
frequency
within
a
mode,
you
must
touch
the
same
function
key
again
to
complete
the
function,
or
you
will
Selecta
different
operating
mode.
This
does
not
apply
to
the
frequency
storage
or
increment
modes.
Section 4
Typical Test Setups
4.2 FREQUENCY COUNTER OFF AIR
This
test
allows
you
to
count
the
frequency
of
8
transmitter
off
air,
this
is
especially
useful
for
identifying
the
frequency
of
unmarked
radios
that
come
in
for
repair.
1)
Connect
the
whip
antenna
to
the
Com
3's
RF
INPUT.
2)
Push
the
COUNT
RF
key,
then
key
the
transmitter,
the
display
will
indicate
the
transmitted
frequency
(in
MHz).
NOTE
You
may
have
to
bring
the
transmitter
within
a
few
-
inches
of
the
Com
3's
whip
antenna
in
order
to
achieve
a
stable
count.
This
is
due
to
the
fact
that
the
Com
3
is
less
sénsitive
as
a
frequency
counter
(typically 25 millivolts) in this mode.

43 FREQUENCY COUNTER DIRECT
CONNECTION
The
Com
3
can
be
used
as
an
RF
frequency
counter
by
connecting
a
50
Q
probe
or
sniffer
loop
to
the
RF
input.
This
is
useful
for
the
alignment
of
crystal
oscillators.
1)
Connect
a
50Q
probe
or
sniffer
loop
to
the
RF
INPUT.
2)
Bring
the
loop
close
to
the
oscillator,
or
connect
the
probe
to
an
appropriate
test
point.
The
Com
3
will
display
the
frequency
in
MHz.
4.4 FREQUENCY/DEVIATION
MEASUREMENTS
The
following
series
of
tests
will
allow
the
measurement
of
the
frequency
and
deviation,
of
the
transmitter,
and
the
PL
tone.
NOTE:
We
will
assume
that
the
transmitter
is
300
Hz
low
in
frequency,
has
deviation
of
7.4KHz,
the
PL
tone
deviation
is
1KHz,
and
the
frequency
of
the
tone
is
high
by
5.0
Hz.
4.4.1 TRANSMITTER FREQUENCY
MEASUREMENT
1)
Connect
the
whip
antenna
to
the
RF
INPUT
jack.
2)
Enter
in
464.15,
then
touch
the
MONITOR
FM
key.
3)
Connect
the
tranceiver
to
be
tested
to
an
antenna
or
dummy
load.((DO
NOT
under
any
circumstances
connect
a
transmitter
to
the
RF
INPUT
of
the
Com3,
serious
damage
will
result.)
4) Touch the. FREQUENCY key, and two red
lights
will
light,
one
on
each
side
of
the
(1.5KHz)bargraph
display.
Touch
the
FREQUENCY
key
again
and
the
(7.0
KHz)
range
is
selected.
Key
the
transmitter,
note
that
only
the
center
LED
is
lit.
5)
Touch
the
FREQUENCY
key
to
select
the
(1.5
KHz
range).
The
first
two
LEDs
from
center
on
the
minus
side
of
the
scale
should
be
lit,
indicating
that
the
transmitter
frequency
is
300
Hz
low.
Adjust
the
transmitter
until
only
the
center
LED
is
lit.
The
transmitter
is
now
exactly
on
464.150
MHz.
42
4.4.2 CTS TONE FREQUENCY
MEASUREMENT
1)
Connect
the
whip
antenna
to
the
RF
INPUT
jack.
2)
Enter
in
-
464.15,
then
touch
the
MONITOR
FM
key
and
the
deviation
key.
`
3)
Connect
the
tranceiver
to
be
tested
to
an
antenna
or
dummy
load.
(DO
NOT
under
any
circumstances
connect
a
transmitter
to
the
RF
INPUT
ofthe
Com
3,
serious
damage
will
result.)
4)
Key
the
transmitter,
(mute
the
microphone
50
no
voice
or
background
noise
will
disturb
the
measurement).
If
too
much
background
noise
or
voice
is
present,
the
frequency
display
will
say
(Error).The
amount
of
background
noise
can
be
observed
on
the
deviation
bargraph
display
(1.5KHZ.range).
Touch
the
AF
COUNT
key,
the
display
should
indicate
the
CTS
tone
frequency
immediatly.
For
our
example
our
tone
should
be
82.5
Hz,
since
it
is
high
by
5.0
Hz
the
display
will
read
87.5
Hz.
Adjust
the
CTS
tone
frequency
until
82.5
Hz
is
displayed.
|
NOTE
If
the
transmitter
is
turned
on
after
entering
the
AF
COUNT
mode,
you
may
notice
an
8
to
10
second
wait
before
the
frequency
display
can
stabilize.
De-
select
and
re-select
the
AF
COUNT
mode
by
touching
the
AF
COUNT
key
twice.The
display
should
stabilize,unless
the
signal
is
too
weak
or
. noisy.
4.4.3 CTS TONE DEVIATION -
" MEASUREMENT
1) Connect the whip antenna to the RF
INPUT jack.
2) Enter in 464.15, then touch the MONITOR
FM key.
| 3) Connectthe tranceiverto be testedto an
antenna or dummy load. (DO NOT under any
circumstances connect a transmitter to the RF
INPUT
of
the
Com-
3,
serious
damage
will
result.)
4)
Touch
the
AF
COUNT
key
to
select
the
AF
COUNT
mode.

5). Touch the DEVIATION key, and two red
lights will light, one on each side of the (1.5KHz)
bargraph display. Turn on the transmitter, mute
the microphone so no voice or background noise
is transmitted. The bargraph display should be
indicating +1 KHz. of CTS tone deviation.
NOTE
Typical CTS tones have a deviation of 0.6 KHz,
therefore, we should adjust the deviation for a
reading of 0.6 KHz.deviation. Four LEDs on each
side of the center LED should be lit, indicating that
0.6 KHz of CTS deviation is seen.
44.4 TRANSMITTER DEVEATION
MEASUREMENT .
1) Connect the whip antenna to the RF
INPUT jack.
2) Enter in 464.15, then touch the
MONITOR FM key.
3) Connect the tranceiver to be tested to an
antenna or dummy load. (DO NOT under any
circumstances connect a transmitter to the RF
INPUT of the Com3, serious damage will result.)
4) Touch the DEVIATION key, and two red
lights
will
light,
one
on
each
side
of
the
(£1.5KHz)
bargraph
display.
Key
the
transmitter,
mute
the
microphone
so
no
voice
or
background
noise
is
transmitted.
Four
LEDs
on
each
side
of
the
center
LED
should
be
lit,
indicating
that
0.6KHz.
of
CTS
tone deviation is seen.
5)
|
Touch
the
DEVIATION
key,
and
two
red
lights
will
light,
one
on
each
side
of
the
(+7.0KHz)
bargraph
display.
Voice
test
the
transmitter,
all
ten
LEDs
on
each
side
of
the
center
LED
should
light
up
with
voice,
indicating
(+7.0
KHz)
of
deviation.
NOTE `
it
is
important
to
adjust
the
CTS
tone
deviation
first,
before
adjusting
the
voice
deviation.Since
the
CTS
tone
will
be
added
to
the
voice
and
will
increase it's overall deviation.
6)
Perform
the
voice
test
again
and
adust
the
transmitter
for
(+5.0
KHz)
deviation.
Six
LEDs
on
each
side
of
the
center
should
light
indicating
a
total
deviation
of
(+5.0
KHz)
including
CTS
tones.
4.5 20 dB QUIETING MEASUREMENT
This test allows you to measure the sensitivity of a
receiver. | i
1) Connect an AC voltmeter to the speaker
terminals of the transceiver.
2) Open the transceiver's squelch and adjust
the volume control for a nominal reading on the AC
voltmeter (for this example; 1 volt).
3) Connect a cable between the tranceiver's
antenna input and the Com 3's RF OUTPUT.
4) Enter in 469.15, then touch the
GENERATE RF,the FM, and 1 KHz keys. The
red light should be "on" next to the GENERATE
RF and FM keys, and "off" nextto the 1 KHz key.
5) Select the X1 range on the attenuator by
touching the LEVEL UP or LEVEL DOWN keys
until
the red
light
next
to
the
X1
is
lit.
(
the
output
range is now 0.1 to 1.0 pV).
6) Increase the output level until the AC
voltmeter
reading
drops
20
dB,
or
to
0.1
volts.
The
setting of the MICROVOLTS knob will be the 20
dB quieting measurement.
NOTE
If
the
receiver
is
not
sensitive,
you
may
have
to
change the attenuation scale to the next higher
range.
Touch
the
X10
key
and
repeat
step
(6)
until
0.1
volts
is
read
on
the
AC
voltmeter
(
the
output
range
is
now
1.0
to
10.0
pv).Keep
going
up until 20 dB of quieting is achieved.

46 12dB SINAD MEASUREMENT
1) Connect a Sinad meter to the speaker
terminals of
the transceiver.
2) Open the transceivers squelch and adjust
the volume control for a nominal reading on the
Sinad meter (inthe black zone).
3) ' Connect a cable between the tranceiver's
antenna
input and the Com 35 RF OUTPUT.
4) Enter in 469.15, then touch the
GENERATE RF and FM keys. The red light should
be "on" next to the GENERATE RF , FM and 1 KHz
keys. ;
5) Select the X1 range on the attenuator by
touching the LEVEL UP or LEVEL DOWN keys
until the red light next to the X1 is lit. ( the output
range is now 0.1 to 1.0 uV).
6) Increase the output level until the sinad
meter reading drops to 12 dB. The setting of the
MICROVOLTS knob wil be the 12 dB Sinad
measurement.
NOTE
If the receiver is not sensitive, you may have to
change the attenuation scale to the next higher
range. Touch. the X10 key and repeat step (6)
until 12dB is read on the Sinad meter. ( The output
range is now 1.0 to 10.0 pv).Keep going up until 12
dB of Sinad is achieved.
—

5.1 GENERAL
The
Com
3
is
composed
basically
of
three
phase
locked
loops,
whose
outputs
are
combined
through
various
mixers
and
amplifiers
to
give
a
final
output
frequency
range
of
100
KHz
to
999.9999
MHz
in
500
Hz
steps.
The
main
VCO
or
PLL
tunes
from
506
MHz
to
1017
Mhz
in
2
MHz
steps,
we'll
Call
that
loop
the
coarse
loop,
since
its
frequency
Steps
coarsely
tune
the
service
monitor's
RFgenerator.
The
fine
loop,
which
tunes
in
500
Hz
Steps,
runs
from
5
Mhz
to
7
Mhz.
The
output
of
the
fine
loop
is
mixed
with
the
506
to
1017
Mhz
loop
in
mixer
X2,
which
produces
an
output
of
505
to
,
1011
Mhz
in
500
Hz
steps.
The
coarse
loop
steps
'
every
2
Mhz
and
the
5
to
7
Mhz
loop,
which
has
a
tuning
range
of
2
Mhz,
mixes
with
the
coarse
loop
to
give
the
finer
resolution
Steps
across
the
entire
band.
Using
general
numbers
we
see
that
one
loop
tunes
from
500
to
1000
Mhz
in
2
Mhz
steps,
and
the
other
loop
tunes
from
5
to
7
MHz
in
500
Hz
steps.
To
obtain
0
to
500
Mhz
from
the
Com
3,
the
output
of
the
coarse
loop
is
mixed
with
another
oscillator
that
runs
at
about
1000
MHz
(
actually
1024
Mhz).
Taking
the
500
to
1000
MHz
.
SECTION
5
THEORY
OF
OPERATION
subtracted
from
1000
you
will
see
that
the
result
is
0
to
500
MHz.
,
Of
the
three
loops,
the
fine
loop,
and
the
coarse
loop
run
continually,
and
the
offset
oscillator
or
loop
(1024
MHz)
is
only
switched
in
for
the
lower
band
of
0
to
500
MHz.
The
final
output
of
allthese
PLLs
is
the
channel
frequency.
Some
form
of
attenuation
is
required
to
give
a
variable
range
from
0.1
uv
to
10,000
w.
This
attenuation
is
performed
in
two
sections,
one
being
a
continously
variable
20
dB,
and
the
other
a
Switchable
step,
0-80
dB.
The
variable
attenuator
is
part
of
the
AM
modulator
section
and
uses
a
double
balanced
modulator
IC.
Its
output,
variable
over
a
20
dB
range,
is
then
applied
to
the
step
`
attenuator.The
step
attenuator
is
controlled
in
20
dB
steps
utilizing
pin
diodes
.
The
signal
is
then
directed
to
the
output
jack.
In
the
receive
mode
the
same
PLLs
are
utilized.
However,
the
input
frequency
of
100
KHz
to
999.9999
MHz
is
applied
to
mixer
X3,
and
mixed
with
the
output
of
the
coarse
loop
(
506
to
1017
Mhz
in
2
MHz
steps).
This
will
allow
the
Com
3
to
receive
frequencies
from
505
-999.9999
MHz.
For
EA
AA
AA
መር
~