NLS FM-7 Instruction Manual

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MODEL FM-7
Frequency Meter

INTRODUCTION

The FM-7 Frequency Meter is the latest in
electronic design. It uses integrated circuits
assembled in a uniquely small package to pro­
vide a fully portable instrument for measuring
frequency. Most important, it can measure
frequency to an accuracy such that it can be
used to verify radio transmission to the tol­
erances established by the FCC for transmis­
sion. Like NLS' LM Series of Digital Multi­
meters, the FM-7 is battery or line operated.
The FM-7 is a rugged, compact, low cost,
wide range instrument of excellent accuracy,
quality and long life. All use a crystal con­
trolled time base for excellent stability and
accuracy.

SPECIFICATIONS

FREQUENCY RANGES: Up to 10 MHz
Up to 60 MHz
INPUT CHARACTERISTICS:
Sensitivity:
30 mV (rms sinewave) - 50 Hz to 30 MHz
10 Hz to 50 Hz
100 mV (rms sinewave) -
30MHz to 60 MHz
Impedance:
1 Mn, < 50 pF up to o. 5 vrms input
1 Mn, < 120 pF above O. 5 vrms input
MAXIMUM INPUT:
±100 vdc
250 vrms - 10 Hz to 500 kHz
•
1. 25 X 10
8
1.25 x 10 V x Hz (vrms = ----) -
- 500 kHz to 25 MHz
5 vrms - 25 MHz to 60 MHz
RESOLUTION:
1 Hz on 10 MHz range
10 Hz on 60 MHz range
ACCURACY:
±1 count (±time base accuracy)
TIME BASE:
Frequency:
Internal Crystal - 2. 097152 MHz
stability:
Aging - <10 ppm/yr
Temperature - ±10 ppm, o•c to +40
Battery Voltage - ±2 ppm, +4.5 to+6.5V
GENERAL:
Display:
7-digit LED. Time between displays:
1 second plus measurement time of 1
second.
Operating Temperature:
°
o·c to +40 c
INSTRUCTION
MANUAL
SPECIFICATIONS (Cont)
Dimensions:
1. 9" H x 2. 7" W x 4. 0" D (48. 26 mm x
68. 58 mm x 101. 6 mm)
Weight:
9 oz (272 g)
Input Cable:
4 ft (122 cm) coaxial, terminated with
miniature alligator clips.
Power:
Four type AA NiCad batteries (charger
unit included).
Discharge Time - 2 hours
Charge Time - 14 hours
May be operated while batteries are be­
ing charged. Overcharge protection is
built in.

OPERATING PRINCIPLES

The FM-7 is a direct counter. It actually
counts the input pulses, one by one, afterthey
have been amplified and conditioned. There
are seven decades in use on the 10 MHz range
(60 MHz maximum). A high quality 2. 097152
MHz crystal is used to establish a precise
one-second time base. During a one-second
&
interval, the pulses are c o u n t e d. For the
next one-second interval, the count is dis­
p 1 a y e d. This two-second sequence is then
repeated.
The display is a multiplexed display of the data
in the counters as they count. Multiplexing
lowers the power requirements for display
while still providing a b r i g h t, easily read
8
display.
Hz
Two ranges are provided; a 10 MHz full scale
range, which with the 7-digit display provides
a one-hertz resolution and a 100 MHz full scale
range, usable to 60 MHz, which has a 10-hertz
resolution.
Because of the 7-digit display, the meter can
be calibrated too. 00001% for a given temper­
ature and battery voltage.

PREPARATION FOR USE

Your frequency meter was shipped from the
factory with a set of four type AA Ni Cad bat­
°
C
teries installed within the case. The batter­
ies are not fully charged. To bring them to
a charged state, plug the charger unit cord into
the meter and then plug the charger unit into
a 115 vac power source. Allow 14 to 16 hours
for the batteries to reach full charge with the
meter not operating. Protection against over­
charging the batteries has been designed into
the instrument.
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©MODEL FM-7
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CAUTION
The instrument will also operate with
non-rechargeable batteries and if this
type is used, NEVER try to recharge
them as they may explode and damage
the meter. The charger unit is designed
to recharge only NiCad batteries.

OPERATION

1. The meter will o p e r a t e from the self­
contained rechargeable batteries with or with­
our the charger unit connected.
2. Connect the input cable to the BNC signal
input connector on the front panel.
3. Rotate the front panel switch to the <60
MHz position. This turns the meter on and
the display will light up.
4. Connect the input cable to the signal to be
monitored. The meter will count the input
pulses and display for one second the total
received for the previous o n e-s e c o n d gate
time. If the meter is in the one-second gate
time at the time it is first c o n n e c t e d, the
reading will be in error as not all pulses were
received. The second sample period will pro­
vide the correct frequency.
CAUTION
Be sure that the input signal does not
exceed the maximum input acceptable.
(See specifications.)
5. If the observed frequency is less than 10
MHz, a zero will be observed as the left-most
digit. If this occurs, change the front panel
switch to the <10 MHz range.
NOTE
Always start with the <60 MHz range,
since the maximum count rate on the
<10 MHz range is 15 to 17 MHz.
6. When m e a s u r i n g a transmitter output
frequency, several methods may be used. If
the output is via a coaxial cable to the antenna,
wrap a wire around the cable five or six times
and connect the FM-7 input red clip to the wire.
Leakage through the shield on the coaxial cable
will provide sufficient signal to the FM-7. If
the antenna is nearby, a simple wire about
eight inches (203 mm) long or more can be
used as a receiving antenna for the meter.
Merely attach the clip to one end of the wire
and hold it parallel to the antenna. The dis­
tance from the transmitting antenna is deter­
mined by the power radiated and the length of
the receiving antenna.