BRUEL & KJAER 2006 User guide

Heterodyne Voltmeter Type 2006
A selective voltmeter covering the frequency range : 100
kHz- 230 MHz. Sensitivity: 50 ftV- 50 V full scale deflect-
ion. Direct reading AM and FM modulation. Fully transist-
orized battery or mains operated .
BRUEL& IK'-'AC.R
NA:.RUM, DENMARK . Teleph. : 800500 . Cable: SRUKJA . Telex: 5316 . COPENHAGEN
030 BB 0078

Heterodyne Voltmeter
Type 2006
March 1969

Contents
l. Description ... . ...... . ... . .. . .......... . . . ..................... . . .
General ........... .. ....... . .. . .... . ........ . ................... .
Input Probe ............. . ..... .. . . .. . .................... . ..... . .
75 Q Input .. . .................... . ..... . .. . ........ ... ....... . . .
Main Unit of Type 2006 ...... .. ........ . .. . .... . . . . . .. .. .. . ....... .
Measuring at the IF -Frequency . ...... . ............ ..... .. . . .. .... .
Rear Connection Jack ....... .. .. . ............. . ..... ... .... . .. . . .
Page
3
3
3
5
5
8
8
The Power Supply .... .. . . ............. . .. . ................. . . ... . 10
2. Control Knobs and Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3. Operation ... . ...... . ......... .. . .. ............... ... . .... .. . . . ... 14
General ........... . ...... . .. . .. . ... . . . . , ... . ........ . . . .......... 14
Reference Adjustments ... ................. . ......... . ..... ... . . ... 14
RF Voltage Measurements . .. ............. . ...... . ... .. . .. ......... 15
Modulation Measurements . . ....... . . . . .. ........... .... ........ . .. 16
4. Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
General ........ . .. .. . . ..... .. ... . ......... .. ......... .. .. . ....... 17
Antenna Distribution System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Automatic Recording of RF Voltages .. . ........ . ... ...... .... . .. . . 21
Directional Characteristics of Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Control of Signal Generator .......... . ........ ... ..... . ...... . ..... 23
Correction Curve .. . .................. . ..... . ... .. . . .. . .. . . .... .... 23
Output Impedance . . .. . ............ . .... . . . .. ... .. .. .. ..... ....... 25
Distortion and Harmonics ...... . ........ .. ... . .. ..... . .. ......... 27
Modulation down to 3 % .. . ........................... . ........... 28
Automatic Recording of Modulation ............. . ..... . .... . .. . .. . . 28
Radiation from AM, FM and TV-Receivers ........ . ..... . ... . .. . ... . 30
The 2006 Used as a Field-Strength Meter .. . ....................... 3U
5. Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

1. Description
General.
The Heterodyne Voltmeter Type 2006 is a transistorized, selective voltmeter
for measuring RF voltages in the frequency range from 100 kHz to 230 MHz.
It is provided with a meter circuit having a maximum sensitivity of 50 pV
for full scale deflection when switched for measuring RF voltages. When
switched for modulation measurements, there will be a full scale deflection
for 80% amplitude modulation (AM) or for a frequency swing of ± 80 kHz
frequency modulation respectively.
The input probe has an impedance of 3 M,Q in parallel with 6 pF, or may be
terminated by a 50 Q resistor.
It is a light weight, portable instrument, which can be operated from the
mains or from a built - in nickel-cadmium storage battery. A unit for recharg-
ing the battery is contained in the instrument.
It is especially useful for measurements on:
Antenna amplifiers and distribution systems for AM, FM and TV Receivers
Transmitters
Transceivers
R.F. circuits
I.F. circuits
The Heterodyne Voltmeter Type 2006 is particularly designed for measuring
the amplitude of high frequency signals and determining the frequency as
well as the percentage modulation. The measured frequency is indicated on
a scale. A meter indicates the amplitude of the measured RF voltage and the
modulation. A loudspeaker provides an audible signal check.
Input Probe.
The miniaturized Input Probe (F ig. 1.1 ) contains an FET stage and features the
advantages of a high input impedance and easy handling due to its small
outside dimensions. The input impedance at 1 MHz is g reater than 3 Megohm
parallel to 6 pF. At higher frequencies the input impedance decreases . At
100 MHz it is about 20 kQ and at 200 MHz it is about 5 k.Q . When using the
Attenuator described below the input impedance is greater than 10 k.Q at
all frequencies up to 200 MHz (C tn = 2 pF ).
A
Capacitive Voltage Divider is provided in order to extend the voltage range
of the voltmeter. The attenuation of the Voltage Divider is 60 dB and the
input capacity is as low as 2 pF. The Voltage Divider is made as a mechanical
3

Attenuotor Probe
~
-=C]
mJ
~
s
a b c d
'- H ~d>
Fig. 1.1.
Input Probe and 60 dB
Attenuator a, b and c: Adaptors.
extension of the input probe (see Fig . 1.1) . The connection from the input
probe to the Voltmeter consists of a multicore cable, which also supplies the
necessary voltage for the probe. At the terminating end, the cable is supplied
with a BNC-connector. The signal pin of the Probe itself can be unscrewed
and replaced with a BNC conversion plug, for instance for calibration purposes
or with a 50 Q termination, see OPERATION, p. 14.
;:::,!.f Vol t
.t f A)]
; ' -..::::.~
i " "'i Ua tor Bott.
Check
1 Mod. 1
L_ ___ __ ~te_r __ ~e~------------------ _j
"' '""9
Fig. 1.2. Heterodyne roltmeter Type 2006. Block diagram.
4

Main Unit of Type 2006.
A
block diagram of Type 2006 is shown in Fig. 1.2. The input stage of the
Heterodyne Voltmeter consists of an untuned mixer stage containing a PNP-
transistor in " ground ed emitter" confi g uration. The sig nal from a variable
oscillator is supplied to the emitter while the collector circuit is tuned to
the IF-frequency, which has been chosen to be 11.3 MHz.
By careful amplitude stabilization of the variable oscillator the conversion
transconductance of the mixer is kept independent of frequency. To further-
more ensure frequency stability the oscillator is temperature compensated
and different oscillator components are used for different frequency ranges.
Following the mixer stage is a crystal filter with a bandwidth of 2.5 kHz.
This filter is shorted when the BANDWIDTH switch is set to "Wide".
From the filter the IF -signd is fed into a 3-stage IF -amplifier via an emitter
follower and a stepped attenuator stage. The IF -amplifier itself is stabilized
by means of current feedback. The first stage of IF -amplification contains a
special diodc-attenuator which is op£rated from the sensitivity controls
marked CARRIER ADJ. and LS AND MOD. ADJ., on the instrument front
panel, respectively. The diode voltage divider avoids different damping levels
influencing the tuned stage. Actually the potentiometers marked CARRIER
ADJ.
and LS AND MOD. AD.J. only determine the working points of the
diodes. Having passed the first two stages in the IF -a mplifier the signal is
-200 -100
I.
+100
+200 kHz
/~ I ~,
~0---- ------ ~ ---- -,~ ~----~~ N----- --~~~-- -- ~ ---------- --~
/ I "" "Wide"
-20
-------- -----1
// I ~~
-30 ------ --~ -+--------~~---- -1~-- -----+--------,_ ~ --------~
/ -5 11 .3 v +S ""
-
40
/
10
• "Narrow" "'-
-30 "'-
;7 ~: ---- ~ -------+------~-------- ~"'.-4
-60 ----------~--------~------ -1~ ------~--------~-- ---------- ~
-~ ---- ------ ~ ---------r-- -----+~ ------~---------r------------ ~
-80 - --+- -+--- ~/\ ~t----+-------1
dB
4654-33
Fig. 1.3. Bandwidth of the Heterodyne Voltmeter in BANDWIDTH switcl1
position "Wide" and "Narrow".
5

"split" so that it is fed both to a Foster-Seeley type FM-detector, and to the
third IF -stage for further amplification after which it is applied to a con-
ventional AM-detector and peak indicating RF-meter.
The demodulated signal is then selected for further amplification in a low
frequency amplifier. Finally the signal is fed to a rectifier for meter detec-
tion, or to a loudspeaker for aural detection. The absolute sensitivity of the
Heterodyne Voltmeter Type 2006 can be checked by means of a built-in
reference oscillator which supplies a highly stabilized voltage to the terminal
marked REF. VOLTAGE on the front plate. Possible sensitivity adjustment
4G54 . i4
Fig. 1.4. FM-Discriminator and IF-Frequency Response (Wide) Characteristics
Oscilloscope setting:
x: 130
kHz/em.
y: Di.'lcriminator curve: 100 mV/cm.
IF-Frequency Response: 10 mV/cm.
6

can be made as described under "Operation", p. 14. To allow the reference
voltage to be independent of whether the oscillator is loaded by 50 [} or by
the high impedance of the Input Probe, the output impedance at the REF.
VOLT AGE terminal is less than 1 .Q. The reference voltage will change by less
than 2% for a 0- 50°C temperature variation.
An overall accuracy of the RF-meter of ± o.5 dB is to be expected in ranges
1, 2, 3, and 4. Better than ± 1 dB in ranges 5 and 6 and better than ± 1.5 dB
in range 7. At the higher frequencies the attenuator must be employed if
capacitive loading is not acceptable.
However, this accuracy is achieved only for voltages well above the level of
dB
~ -~---4--4---4---+4-~~~+--+-~-~~+-~~--+-~
100
200 500 1000 2000 50 000 100 000 200 000 500 000
Frequency (kHz)
Fig. 1.5. Sensitivity of the Heterodyne Voltmeter Type 2006.
dB/1J
I
\2o
Bandwidth
Position '"Wide''
\
should not be .1.
I
used below 6MHz
+15
+10 \.. I Probe
''jide'"
I Probe '"Narrow'"
+ 5 !
I
- 5
100 200 500 1000 2000 5000
10 000 20 000 50 000 100 000 200 000 500 000
Frequency/ kHz
469 002
Fig. 1.6. Inherent Noise of the Heterodyne Voltmeter Type 2006 (50 ftV range)
7

inherent noise in the Heterodyne Voltmeter. In Fig. 1.5 is shown typical
curves of sensitivity and Fig. 1.6 shows the inherent noise for the Heterodyne
Voltmeter.
Input voltages around the noise level can be measured by comparison with a
reliable standard signal generator.
A limitation of the measuring range will occur at the lower frequencies of
the input signal for which the corresponding oscillator frequency approaches
the IF and tends to block the IF -amplifier. Consequently, the higher the
frequency is, the lower the level of the measurable input voltage. As indicated
in Fig. 1.5 this limitation is small compared with the frequency range of the
instrument.
Measuring at the IF-Frequency, 11.3 MHz.
The sensitivity of the Heterodyne Voltmeter Type 2006 will change at fre-
quencies just around 11.3 MHz, which is the center frequency of the IF-
amplifier. Depending on the setting of the BANDWIDTH switch it will
increase (Wide) or decrease (Narrow) as shown in Fig. 1.7a. At f = 11.3 MHz
it is
thus only possible to make measurements if the FREQUENCY RANGE
switch is set out of position (between 7 and 1). The oscillator is then dis-
connected, and the frequency response of the Heterodyne Voltmeter will be
as shown in Fig. 1. 7b when the BANDWIDTH switch is set in position
"Wide". As the sensitivity under these circumstances depends on the current
amplification factor of the Mixer transistor, the Heterodyne Voltmeter must
in this case be calibrated specially with a known signal voltage at 10.7 MHz.
Rear Connection J aek.
On the rear plate is a 6-pinned jack to which the following internal connec-
tions are made: Fig. 1.8).
External Battery.
The built-in battery is connected directly to the jack, pins 1 and 5. Therefore
the intenral· 'bTJ.ttery should be removed if an external battery . is connected to
teh terminals. The external battery must have the positive terminal connected
to pin 5.
LF-Output.
The output for external loudspeaker connected directly across the LF-
output should not be loaded with more than 60 Q, and in this case the fre-
quency response is ± 1 dB from 20 Hz to 20ooo Hz. The LF output is found
at pins 2 and 4.
Meter Circuit.
The terminals 3 and 4 can be used for connecting an external meter or ampli-
fier. Pin 4 is connected to the chassis ("ground") and pin 3 is connected to
the meter circuit in series with a 63 kQ resistance.
The Power Supply.
The Heterodyne Voltmeter Type 2006 is designed for battery-operation. The
battery is contained in the instrument and is of the nickel-cadmium storage
8