RADIOMETER AFM2 User manual

AFM2 ,
MODULATION
METER
1

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MODULATION
I
RADIOMETER n
: BDE
0
COPENHAGEN U
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I
This instruction manual is valid for the Modulation Meter, type AFM2, but applies also
for the type AFM2S6 when the following specification changes and additions are borne
'
in mind:
1) On page 05 read for AFM2S6
AMdistortion:
Carrier frequencies within
the range
5 - 300 MHz: 0.3% distortion at 30% AM
cmd at modulation
frequencies,within 20 Hz
- 1~'kHz.
1.5% distortion at 90% AM and at modulation
frequencies within
10 Hz - 50 kHz.
Carrier frequencies within
the range 300
- 1002 MHz: 1.5% distortion at 30% AMand at modulation
frequencies within 10 Hz -.50 kHz.
2) Signal-to-noise ratio for each stereo channel measured with a psophometer:
Typically 66 dB at f40 kHz frequency deviation and RF
< 200 MHz. These data apply
only when the level of the RF signal
is in the 30 - 100 mV range.
Furthermore, it applies to the Modulation Meter, type AFM2S4S5, when the following
corrections are made on pages
06, 07, D6, E2, and E4:
1 ) AF Output Nominally
0 dh(0.775 V rms into 600R)
when meter reads 3/4 of fulI-scale deflection,
e.g., at *75 kHz deviation in the f 100 kHz
deviation range.
2) AF Output Terminals 3-pol e standard, type
ZNA 333874/1
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Table of Contents
SECTION A - INTRODUCTION
SECTION
B - SPECIFICATIONS
SECTION C
- ACCESSORIES
SECTION D
- GENERAL DESCRIPTION
1, Description
2. Controls, Meters, and Terminals
SECTION
E - OPERATING l NSTRUCTIONS E 1
1, Connecting the Instrument E 1
2, Measuring Ampl itude Modulation Percentage E 1
3. Measuring Frequency Deviation E3
4, Using a Crystal Oscillator Plurin Unit, code 900-252 E4
SECTION F - TECHNICAL DESCRIPTION F1
1, RF Input Circuit
2, Tuner
3. IF Filter
4,
IF Preamplifier and IF Attenuator
5, IF Amplifier
6,
P hase-compensator and Ehnd-pass Filter
7, Buffer Amplifier
8. AM Detector
9, IF Output Amplifier
10, Limiter Stages
11, FM Detector
12, AF Amplifier
I and I1
13, AF Amplifier Ill - V
14, AF Detector
1 5, Power- Supply
SECTION
G - MA1NTENANCE
SECTION H
- PARTS LIST
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Modulation Meter
Type AFM2
Section A. Introduction
Fig .A1 . The I'tAodulation i'Aeter,
type AFM2.
The Modulation Meter, type AFM2, is
a solid-state, line- or battery-operated
precision measuring instrument for ac-
curate measurement of the modulation
depth of AM signals and the peak devi-
ation of
FM signals in the carrier fre-
quency range from
5 to 1002 MHz. The
Modulation Meter
is designed for ac-
cepting telemetric signals with a modu-
lation frequency up to 200 kHz, and
stereo signals for which it features an
L/R-separation of 46 dB.
The indicating metel- has fuI I -scale de-
flection for
3, 76, 30, and 1 0C9h AM,
and 53, *1C, k3C1 If;GC, and zt2C.C
kti~ t hl\, peak value. Due to the vely
srnall amount of residual modulation
generated in the idiodulation Meter plop-
er, it is possible to measure residual FM
and AM in oscillators, sp~~rious AM on
F"M signals, and vice versa. Accilrate
measurer(enfs on distol-ted signuls are
rendered easy by a swit2l.l that enables
the positive and the negative peak val-
ue to be measured separately. If in-
creased resolution
is desired, an exter-
nal indicator, such as a voltmeter,
con
he e--plo)/ed to extend ihe measuring
ranges downwards.
The input signal level necessury for full
occbracy is 3 mV in the carrier frequen-
cy range
5 to 200 MHz, 20 mV in the
range
2CC to 60C Mtlz, and 30 mV in
the range SCO to 1003 MHz. The maxi-
mcim operating input voltage is 10 V.
Besidzs a manual level control, the
Modulation Meter features an automatic
level control with a regulating range
of
40 dB.
To increase the versatility of the Mod-
ulation Meter for nreasvren;ants on nar-
row-band equipment, it
is provided with
two
IF bandwidths of *20 and k400
kHz, just as three standal-d deen~phasis
networks of 50, 75, and 750 s, one
non-standard of
6 dB/octave (ref. 1 kHz),
four low-pass filters with frequencies of
3, 15, 75, and 200 kHz, and ore band-
pass filter with
3 dB points at 50 Hz and
15 kHz, ensure optimal measuring condi-
tions for a wide range of applicatio~s.
A Crystal Oscillator Unit, code
900-252,
is available. See SECTION C,
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Section B. Specifications
FREQUENCY RANGE OF
INPUT SIGNAL 5
- 1002 MHz
FREQUENCY RANGE OF
VARIABLE OSClLLATOR
7 - 1000 MHz
Fundamental ranges: 7-12, 12-21, 21 -37, 37-65, 65-1 10, and
110-200 MHz
Harmonic ranges: 200-330, 330-600, and 600-1 000 MHz
CALIBRATION ACCURACY 3%
CRYSTAL OPERATION An optional Crystal Oscillator Unit, code 900-252,
that accepts up to four switch-selected crystals, en-
sures low residual FM.
Specification changes due to crystal operation: See
SECTION C
- ACCESSORIES.
INPUT LEVEL
Carrier frequency ranges:
+
Attenuation 0 dB :
Attenuation 10 dB:
Attenuation 20 dB:
Attenuation 30 dB:
Attenuation 40 dB:
One input socket in connection with a 3-step input
attenuator (10
+ 10 + 20 dB) ada,pts the AFM2 to
input levels from
3 mV to 10 V.
5-200 MHz 200-600 MHz 600-
1 000 MHz
+
Basic sensitivity range, BSR
4-t
Values in parentheses are derived from minimum level
of
BSR and from lower limit of overlapping ranges.
Max. safe input level: 10 V
Input level for residual
FM and AM measurements:
I Min. input level ( RF attenuation inserted (dB) I
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l NPUT IMPEDANCE
LEVEL
SETTING
Manual level setting:
Automatic level setting:
50 R nominal
Continuous within a range of min.
40 dB.
The AGC system keeps the level setting within
0.5% for input level variations within the speci-
fied input level ranges, inclusive of the overlap-
ping ranges.
Fine adjustment of the automatic level setting
is
possible .
FR EQ LI E NCY
MODULATION
Deviation ranges:
*3, *lo, k30, lt100, and *300 kHz f.s.d. (peak
deviation).
Positive and negative deviation peaks can be mea-
sured separately.
Accuracy:
*75 kHz deviation:
$300 kHz deviation:
2% of reading
+ 1 % of full scale at modulation fre-
quencies within
20 Hz - 53 kHz
4% of reading + 1% of full scale at modulation fre-
quencies within
10 Hz - 75 kHz.
2% of reading
-t- 1% of full scale at modulation fre-
quencies within
20 Hz - 15 kHz.
7% of reading + 1 % of full scale at modulation fre-
quencies within
10 Hz - 125 kHz.
15% of reading
+ 1% of full scale at modulation fre-
quencies within 125 kHz
- 200 kHz.
Notes:
1. To obtain specified accuracy, the upper frequen-
cy limit of the built-in low-pass filter should be
switched as follows:
Deviation range upper frequency limit
k3 kHz
3 kHz
k10 kHz 15 kHz
*30 kHz 15 kHz
&I00 kHz 75 kHz
A300 kHz 200 kHz
(see ~andwidths)
2. The specified accuracies are valid only with the
METER switch set to SLOW. In position FAST, the
lower frequency limit
is 160 Hz.
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Distortion
k75 kHz deviation:
k300 kHz deviation:
0.1 % distortion at modulation frequencies within
10 Hz -, 15 kHz.
0.2% distortion at modulation frequencies within
20 Hz - 53 kHz.
0.3% distortion at modulation frequencies within
10 Hz - 75 kHz.
0.5% distortion at modulation frequencies within
20 Hz - 15 kHz.
1 .5% distortion at modulation frequencies within
10 Hz - 50 kHz.
3% distortion at modulation frequencies within
10 HZ - 125 kHz.
5% distortion at modulation frequencies-within
125 kHz - 200 kHz.
LR-separation of
FM stereo signals: For an ideal FM stereo signal (FCC and EBU-stan-
dard), the LR-separation at modulation frequencies
within
40 Hz - 15 kHz is greater than 46 dB.
AF output and meter response (FM):
AF output: Within
40 Hz - 15 kHz, the LR-separation is greater
than
46 dB (see above). This corresponds to a depar-
ture from a linear phase response of less than
0.5'
and a frequency response within +0.25% and -1.5%
(40
HZ - 53 kHz).
Note: 'The built-in
200 kHz low-pass filter is to
be used.
Meter response:
Residual
FM:
Within 40 Hz - 53 kHz, the frequency response
of the meter
is within +0.25% and -1.5%.
Notes:
1. The built-in 200 kHz low-pass filter is to be
used.
2. The specified response is valid only with the
METER switch set to SLOW. In position FAST,
the lower frequency limit
is 160 Hz.
On condition of a quiet test room (noise level
< 60 dB rel. 2 x 10-4 pbar.):
Less than 25 Hz FM (r.m.s.) within the frequency
range
5-250 MHz; typically 15 Hz (r.m.s.).
Less than 100 Hz FM (r.m.s.) up to 1002 MHz,
typically
50 Hz FM (r.m.s.).
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Notes:
1 . 0.1 % of ful l deviation range is to be added.
FM due to AM:
Deemphases:
Standard deemphases:
Deemphasis:
2. Minimum RF input level: See input Level.
3.
the built-in band-pass filter (50 Hz - 15 kHz)
or one of the deemphases (50 ps or 75
t~s) is to be
used.
Additional residual
FM error due to AM is typically
less than 50
Hz (r. m.s.) at 50% AM, when the band-
pass filter (50 Hz
- 15 kHz) is used.
50,
75, and 750 ps, switchable.
6dB/oct. (ref. 1 kHz). For frequency response of
filter, see Fig.
€31 .
The deemphasis can be switched off.
Fig.
€31 . Frequency response of
the
6 dB/oct. filter.
AMPLITUDE MODLILATION
Modulation depth range: 3, 10, 30, and 100%
AM f.s.d.
.
Positive and negative modulation ~eakscan be mea-
sured separately.
Accuracy:
Manual level setting: 2% of reading
+ 1% of full scale at modulation
frequencies within 20 Hz
- 15 kHz.
5% of reading
+ 1 % of full scale at modulation
frequencies within 10 Hz
- 50 kHz.
Notes:
1. To obtain specified accuracy, the upper frequency
limit of the built-in low-pass filter should be switched
as follows:
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Automatic level setting:
modulation range upper frequency range
+
3% 3 kHz
10% 15 kHz
30% 75 kHz
1 00% 200 kHz
+
By a 10 dB increase in minimum input level, the
upper frequency limit can be extended to 15 kHz.
2. The above accuracies are valid for modulation
depths up to 90% AM within the carrier frequency
range 15-300 MHz, and up to 30% AMwithin the
carrier frequency range 300-1 002 MHz.
The following typical values are to be added to
the above accuracies:
At a modulation frequency of 20 Hz:
6% of reading.
At a modulation frequency of 50 Hz:
1 % bf reading.
At modulation frequencies above 100 Hz, the addi-
tional error is negligible.
Note: The specified accuracies (manual and automat-
ic level settings) are valid only with the
METER switch
set to SLOW. In position FAST, the lower frequency
limit
is 160 Hz.
1
AM distortion:
Carrier frequencies within
the range
5 - 300 MHz: 0.2% distortion at 30% AM and at modulation fre-
quencies within 20 Hz - 15 kHz.
1% distortion at 90% AM and at modulation frequen-
cies within
10 Hz - 50 kHz.
Carrier frequencies within
the range 300 - 1002 MHz:
1 % distortion at 30% AM and at modulation frequen-
cies within 10 Hz - 50 kHz
Residual
AM at CW: Less than 0.03%
AM (r.m.s.) at carrier frequencies
up to 200 MHz.
Less than 0.1
% AM (r.m.s.) at carrier frequencies
up to 500 MHz.
Less than 0.3% AM (r. m. s.) at carrier frequencies
up to 1002 MHz.
Notes:
1. 0.1% of full AM range to be added.
2. Minimum
RF input level: See Input Level.
3. The built-in band-pass filter (50 Hz
- 15 kHz)
is to be used.
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AM due to FM:
Additional error is less than 0.6% AM (r. m.s.)
at 550 kHz deviation.
AF output
(AM)
Manual level settings: 'the frequency response
is within 50.5% in the
range 20 Hz
- 15 kHz.
Automatic level setting: The following typical error contributions are to be
added to the above frequency response:
At a modulation frequency of 20 Hz:
6%
At a modulation frequency of 50 Hz: 1 %
At modulation frequencies above 100 Hz, the error
contribution
is negligible.
l NTERMEDIATE FREQUENCY CHANNEL
Frequency: 2 MHz
Bandwidths:
IF check:
IF outputi
AUDIO FREQUENCY CHANNEL
Bandwidths:
3 kHz filter:
15 kHz filter:
75 kHz filter:
200 kHz filter:
approx. *400 kHz/3 dB and 525 kHz/3 dB, switch-
selected.
The meter has a separate scale to facilitate correct
tuning
(IF = 2 MHz).
2 MHz IF signal of 0.2 V EMF from 50 Q source at
correct frequency tuning and full scale deflection on
meter.
four switchable low-pass filters, 3 kHz, 15 kHz,
75 kHz, and 200 kHz, to be used when measuring
FM deviation and AM modulation.
for mod. freq. up to
3 kHz
for mod. freq. up to 15 kHz.
for mod. freq. up to 75 kHz and for measurements
of
FM stereo deviation.
for mod. freq. up to 200 kHz and for measurements
of stereo
L/R separation.
(bandwidth: 10 Hz (0.1 dB)
- 350 kHz (3 dB) )
50 Hz - 15 kHz filter: Band-pass filter, 50 Hz (3 dB)
- 15 kHz (3 dB),
to be used when measuring residual
FM and AM.
AF output: AF signal of
1 V EMF (peak value) at full scale
deflection.
Bandwidth as specified above.
A switch provides for
ac- or dc-coupl ing.
ac-coupl ing: Output impedance: 600
Q in series with
10 pF.
dc-coupl ing: Output impedance; 600 Q.
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dc OLITPUTS
IF level:
IF frequency:
Modulation:
POWER
SUPPLY
Power line:
dc-voltage of
1 V EMF from 600 R source at meter
deflection to set level mark.
dc-voltage of
1 V EMF from 600 R source at meter
deflection to
IF CHECK mark (50 mV/100 kHz).
dc-voltage of 1 V EMF from 500 5: source at full
scale deflection.
VoItages:
Frequencies:
Consumption:
110 V and 220 V, ~10%.
48 - 65 HZ.
about 25 VA.
The power cord is fixed and provided with a mains
plug of the Schuko type.
External dc supply:
dc sources:
Current drain:
0 to +(I8 to 25 Lq and 0 to -(I8 to 25 V) .
approx. 400 mA from each source.
TERM1 NALS
RF input and IF output:
AF output:
dc output
(AF):
External - dc supply:
Operating ambient temperature
range:
DIMENSIONS AND
WEIGHT
Height:
Width:
Depth:
Weight:
MOUNTING AND FINISH
ACCESSORIES SUPPLl ED
ACCESSORIES AVAlLABLE
B NC
UHF
Banana jacks
Bel
l ing Lee 1.1 436;'s
197 mm (7 3/4 in.)
485 mm (19 1/8 in.)
245 mm (9 5/8 in.)
13 kg (28.6 Ibs)
Steel cabinet finished in grey enamel lacquer.
1 coaxial cable (50 O), code 017-004, with
type UG-88/U BNC plugs.
1 battery plug, Belling & Lee, L1436/P, code 805-429.
Crystal Oscillator, code 900-252.
1 set of dust covers (top plate and bottom plate)
for rack mounting, code 884-002
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Section C. Accessories
PLUG-IN CRYSTAL OSCILLATOR UNIT,
CODE 900-252
General
The Plug-in Crystal Oscillator Unit,
code 900-252,
is preferably used with-
in the frequency range 80
- 1000 MHz
to achieve low residual FM. It is sup-
plied without crystals.
The Crystal Oscillator Unit contains
a
crystal-controlled oscillator followed by
a doubler stage, and it has room for up
to four switch-selected crystals. The
crystals are mounted inside the unit and
can easily be exchanged. Initial adjust-
ment
is made by means of individual
Fig.
C1. The Crystal Oscillator Unit,
code 900-252.
screw-driver adjustments on the front
panel
.
The trimmers directly cover a tuning
range of 360
- 1000 MHz. In the ranges
80
- 120 MHz and 250 - 360 MHz, a
fixed capacitor must be added in parallel
with the trimmer.
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Specifications
Number of crystals:
Frequency of crystals:
lnitial conditions:
Characteristics of the crystals:
Type:
Frequency:
Frequency tolerance:
Frequency tolerance over
operating temperature range:
Condition of resonance:
Mode of operation:
Max. drive level:
Max. equivalent series
resistance:
sockets for up to
4 crystals.
In order to achieve the highest possible sensitivity
of the modulation meter, the frequency of the crys-
tals must be as high as possible. Overtone crystals
having frequencies within the range 40
- 100 MHz
are recommended. The crystal frequency f
is de-
cr
termined by
f -2
s
f=
cr 2n MHz
where f indicates the carrier frequency and n the
s
odd harmonic of the crystal overtone-frequency.
The sensitivity specifications, item
l NPUT LEVEL,
are based on the following combinations of carrier
frequency, order of harmonic, and range of crystal
frequencies.
HC-25/U
See above.
0
10 x at reference temperature 25
C
Carrier frequency
f
s
250 - 600 MHz
600 - 1000 MHz
10 x within 0-50'~
Series
5. overtone
2 mW
Order of harmonic
n
3
5
Range of crystal
frequencies
fcr
40- l00MHz
60 - I00 MHz
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CHANGE IN SPECIFICATIONS OF AFM2
CAUSED BY THE CRYSTAL OSCILLATOR
lnput level:
Frequency ranges: 250
- 600 MHz 600 - 1000 MHz
+
Attenuation 0 dB : 20 - 100 mV 30 - 100 mV
Attenuation 10 dB: (60)*
- 100 - 300 mV 100 - 300 mV
Attenuation 20 dB (200)
- 300 - 1000 mV 300 - 1000 mV
Attenuation 30 dB: (0.6)
- 1 - 3 V 1 -3V
Attenuation 40 dB: (2)
- 3 - 1OV 3-10V
+
Basic sensitivity range, BSR
u
Values in parentheses are derived from minimum
level of
BSR and from lower limit of*overlapping
ranges.
Max. safe in~utlevel: 10
V
lnput level for FM and AM
measurements:
250
- 600 MHz:
600
- 1000 MHz:
Residual FM:
I Min. input level 1 RF attenuation inserted (dB) I
1 Min. input level 1 RF attenuation inserted (dB) (
Less than 20 Hz FM (r.m.s.) at carrier - frequencies
up
to 1002 MHz; typically 15 Hz (r.m.s.).
1 . 0.1 % of fu 11 deviation range is to be added.
2. Minimum RF input level: See lnput Level.
3. The built-in band-pass filter (50 Hz
- 15 kHz)
or one of the deemphases (50 ps
or 75 ps) is to be used.
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Residudl AM at CWo
Less than 0.15% (r. m. s.) at carrier frequencies up
to 1000
MHz.
Notes:
1 . 0.1 % of full AM range must be added.
2. Minimum RF input level: See Input Level.
3. The built-in band-pass filter (50 Hz - 15 kHz)
is to be used.
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Section D. General Description
DESCRIPTION
As can be seen on the simplified block-
diagram shown in
Fig. Dl , the RF input
signals to the 50
Cl coaxial connector
are fed to a diode mixer via an input
attenuator providing for 10, 20, 30,
and 40 dB attenuation and thus accom-
modating
RF signals from 3 mV to 10 V
r.m.s. The mixer, which is balanced
and highly linear, so that distortion of
amplitude-modulated signals
is avoided,
is coupled to the local tuning oscillator.
For
RF input signals in the range from
5 to 200 MHz, mixing
is realized with
the fundnmental frequency of the local
oscilla:or, whilst it takes place with
the third and fifth harmonics in the
range from 200 to 1002 MHz.
This re-
sults in an
IF signal of 2 MHz. The
mixer can also be coupled to an option-
al Crystal Oscillator Unit, code 900-
252, which can accommodate four crys-
tals, thereby enabling measurements at
four predetermined, fixed frequencies.
the signal from the mixer is passed
through an IF filter, which
is a phase-
linear band-pass filter with
a bandwidth
of 1400kHz, a high degree of phase-
linearity being necessary in order to
pass a multiplex stereo signal with min-
imum distortion.
From the
IF filter, the IF signal is fed
to an
IF preamplifier which acts as a
buffer. At the same time, the
IF pre-
amplifier provides for ahplification of
the IF signal.
This amplification, to-
gether with ideal coupling to the
IF
filter, keeps the noise level down to
a minimum at all input levels.
The
IF preamplifier is followed by a
diode attenuator whose biasing current
can be controlled
by the potentiometer
LEVEL, accessible on the front panel of
the Modulation Meter. Level control can
be performed within a range of 40 dB.
Alternatively, the
IF attenuator can be
driven by a voltage proportional to the
IF level amplified in an AGC amplifier.
This provides for automatic level control
within 40 dB. Fine adjustment
is never-
theless also possible by means of the
potentiometer
LEVEL.
The IF signal from the IF attenuator is
then fed to an IF amplifier which can-
sists of two wideband amplifier stages.
The
IF amplifier brings the IF signal to
the level required by the
AM detector.
The amplified 1F signal is then passed
either through
a band-pass filter or
through a phase-compensator, according
to the position of the
IF BANDWIDTHcon-
trol
. The band-pass filter has a band-
width of
A25 kHz and is phase-linear
just as the IF filter. It is intended for
use when measuring on weak signals
from narrow-band equipment. The phase
compensator leaves the initial bandwidth
unchanged.
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A buffer amplifier separates filters, AM
detector and
IF output amplifier. It con-
sists of a unity-gain amplifier with low
output impedance and serves to suppress
any influence from the
IF output which
is available for external monitoring from
a coaxial connector on the front panel.
The
IF signal from the buffer amplifier
is fed both to the AM detector and to
the
IF output amplifier. The AMdetec-
tor
is an amplifier with a mean-value
detector in the feedback loop which
also provides for the large amount of
linearity required. The AM detector has
a dc and an ac output. The first of
these
is coupled to the meter of the in-
strument via the FUNCTION selector.
In the corresponding position of the
FUNCTION selector, the meter indi-
cates the value of the AM detector's
dc current
- in other words: the IF lev-
el. The second output of the AMdetec-
tor
is coupled to the AF section (described
below) via the selector FUNCTION.
As stated above, the
IF signal from the
buffer amplifier
is also fed to the IF
output amplifier which provides for am-
plification so that the level required for
driving a following limiter
is obtained.
The limiter transforms the
IF signal into
a square wave, the zero crossing of
which
is controlled by variations in the
peak-to-peak value being compared with
variations in the mean value. Subsequent
limiting action takes place inthe follow-
ing limiter section. The resulting signal
is fed via a buffer amplifier to the FM
detector section which consists of a
monostable multivi
brator and an output
amplifier.
The signal from the last limiter section
is used to trigger a monostable multi-
vibrator which provides for pulses of
constant width. The pulses from the mul-
tivibrator are amplified in an output am-
plifier. The output amp1ifier
is provided
with a regulating loop consisting of a
peak detector and an amplifier.
This
regulating loop keeps the value of the
peak-to-peak voltage of the output am-
plifier constant. Hence, as the amplitude
and the width of the pulses are constant,
the mean value of the signal will vary
according to the number of pulses per
second. The mean value
is utilized
when the FUNCTION selector
is inpo-
sition IF CHECK for reading the value
of the intermediate frequency. To ensure
a high degree of accuracy and an extreme-
ly low hum level, both the multivibrator
and the output amplifier are furnished
with their own regulated power supply.
From the AMor
FM detector, the signal
is fed to a low-pass filter via a relay
controlled by the FUNCTION selector.
The low-pass filter features the high de-
gree of phase-l inearity required for pass-
ing stereo informationwithout any disturb-
ing influence on
L/R separation.
The low-pass filter
is followed by a
two-section,
4 x 10 dB precision atten-
uator which determines the metering
ranges.
It is followed by an amplifier
providing for amplification
of the AF
signal to the level required by the next
stages.
The AF amplifier
is followed by deem-
phasis networks providing for the stan-
dard deemphases of 50, 75, and 750
pi,
and the non-standard deemphasis of 6
dB/oct. The amplified AF signal can
also be passed through one of four low-
pass filters with frequencies of 3, 15,
75 and 200 kHz, or through a band-
pass filter with 3 dB points at 50 Hz
and 15
kHz, ensuring a wide range of
applications.
These networks and filters are followed
by an AF amplifier. The output signal
from this amplifier
is available on the
front panel via the AF OUTPUT con-
nector for distortion measurements or
external monitoring. Loading of the AF
OUTPUT does not interfere with the me-
ter indication. The output voltage from
the first AF amplifier
is also fed to an-
other AF amplifier providing for the
voltage necessary for the AF detector.
The signal from the AF OUTPUT can
either be dc-coupled or ac-coupled to
Scans by ArtekMedia © 2008

Fig. Dl . Block-diagram of the Modulation Meter, type AFM2.
ROMAN FIGURES REFER TO
DIAGRAM NUMBER
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/
R F Local
q- Att. / -
osc.
/
t
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-
/
R F
Input Mixer
v
I
-
11 I F
111
IF
Output
1 L \r
VI
7, 7,
VII
IF Frequency
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4s 10 2"
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\
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-
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Att. - Pass
\
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Filter
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Filters
Deem-
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- IF Level
-
x
Scans by ArtekMedia © 2008