ZKT - LABORATORY
5. BASIC PARAMETERS OF RADIO RECEIVER
5. BASIC PARAMETERS OF RADIO RECEIVER
Goals of measurement
Measure following parameters of the communication receiver:
1) Sensitivity
2) AGC characteristics
3) AGC response time
Measuring equipments
Communication receiver AOR AR 5000
Stereo-wattmeter (with standard load 8 Ohm)
Signal generator Rohde&Schwarz SMY 02
Oscilloscope Tektronix TDS 3012B
AF
Amplifier
+Filter
3 IF
AM
Demodulator
1 IF
2 IF
+ Bank of
filters
Input
Stage
RF
Generator
Measurement block diagram
uaf
Oscilloscope
Stereowattmeter
+Load 8 Ohm
AGC output
Fig. 1: Measurement block diagram
Introduction
Radio receivers allow selectively separate and further process a signal selected from
the spectrum of electromagnetic waves picked up by the antenna. Superheterodyne
configuration of radio receivers according to Fig. 2 is widely used.
fs
Input
Circuit
RF
Amplifier
fs
Mixer
fIF
IF
Amplifier
Demodulator
AF
Amplifier
fo
Oscillator
Fig. 2: Block diagram of a heterodyne receiver
A selective input circuit separates a signal carried at one selected frequency fs from
those at all other frequencies. This signal is amplified in following HF amplifier. The
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5. BASIC PARAMETERS OF RADIO RECEIVER
undesired signals, which frequencies are far from desired signal, are there suppressed.
Frequency conversion is achieved in frequency converter mixer by mixing the received signal
of frequency fs with a local oscillator (LO) signal of frequency fo to obtain an intermediate
signal IF (intermediate frequency)
fIF = fo - fs (fo > fs).
By arranging for the local oscillator to be tuned simultaneously with the input circuit across
the band intermediate frequency fIF will always be constant. Following IF amplifier than can
operate at only one frequency fIF. A high gain and also a high selectivity and sensitivity are
produced. Depending on the application there may be one, two or three frequency
conversions. The last IF amplifier output is applied to the demodulator. This circuit derives
from the IF signal the modulating (AF) signal, which may be amplified by the base band (BB)
amplifier to the level required for output.
The measurement will be performed on the Japanese communication receiver AOR. It
is superheterodynne receiver with three frequency converters. Its basic architecture is on a
Fig. 3 and technical parameters in tables 5, 6 and 7. This receiver serves both professional and
radio amateur monitoring analog radio services in bands 10 kHz - 2600 MHz with different
types of modulation (FM – frequency modulation, AM – amplitude modulation, SSB – single
side band modulation, CW – continual wave and so on). Different antennas are fit for
different radio bands and therefore the receiver is equipped with several antenna inputs. The
receiver is also equipped with the bank of adjustable IF filters (see table 7) for different types
of radio services. Automatic gain control function (AGC) secures a constant volume at the
speaker even though the signal strength at the antenna may vary widely (of 100 dB or more).
Measurement notes
The measurement will be performed in accordance with standard RTCA
(Requirements and Technical Concepts for Aviation) for airborne radio communications
equipment operating within the radio frequency range 117,975 – 137 MHz.
Basic HF generator setting:
Carrier frequency (RF) 130 MHz, amplitude modulation (AM); modulation index 30% and
modulation frequency (AF) 1 kHz (standard values); level (LEVEL) 100 µV.
Communication receiver setting:
A small knob placed in the lower right corner can set communication receiver. Setting is
confirmed by pushing the key (ENT), a wrong choice can be cancelled by the key CLR.
Check out or set following parameters:
• VFO: key (VFO) – press the key repeatedly until the required VFO is chosen - VA is
displayed in the lower right corner of the LCD (this choice allows a manual receiver
setting).
• Modulation: key (MODE) - AM
• Antenna: FUNC – ANT (key (ATT)) - antenna 1
• Attenuator: key (ATT) – 0 dB for task 1); 10 dB for task 2) and 3)-see measurement tasks
• AGC: FUNC – AGC (key (STEP)) - FAST
• Gain: FUNC – RF GAIN (key (6)) - manual setting (N-SQL is not displayed)
- chose maximal gain by rotating squelch control SQUELCH anticlockwise (note: The
squelch control is used to eliminate unwanted background noise by the different
configuration of the receiver)
• IF bandwidth: FUNC – IF BW (key (3)) - 6 kHz
• AF output: FUNC – AF.SET key (MODE)) – next by choice UP/DOWN
- Low pass filter: A–LPF - 3 kHz
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5. BASIC PARAMETERS OF RADIO RECEIVER
- High pass filter: A–HPF - 300 Hz
- De-emphasis switched off – DE.EMP - THRU
• Frequency 130 MHz
• Volume: volume control AF GAIN – set on output power 50 mW (read on the stereowattmeter by the basic HF generator setting)
Select standard load 8 Ω on the stereo-wattmeter.
Task 1)
A receiver’s sensitivity refers to the ability to produce an acceptable sound from weak
signals. The sensitivity is determined namely by a receiver’s gain and its noise characteristics.
Maximum sensitivity describes the ability to amplify weak signals without respect to receiver
noise characteristics. When the gain is sufficiently high, the weakest signal power that may be
processed satisfactorily is noise-limited, which is represented by the sensitivity (noise limited
sensitivity, effective sensitivity). The sensitivity is the minimum level of the standard
modulated input signal when the receiver is adjusted to produce the standard output by
selected S/N (x dB). Manufacturer usually specifies standard output; other standard
parameters are defined by standards. All standards for AM receivers employ sinusoidally
modulated input signal with modulation index 30% and modulation frequency 1 kHz, S/N
depends on type of a receiver [radio receivers 26 dB (by standard ČSN IEC 315-3),
communication receivers 10 dB, aviation receivers 6 dB].
Receiver sensitivity measurement block diagram is on the Fig.1. RF signal generator is
connected to the antenna input of the receiver; standard load 8 Ω is connected to the output
instead of speaker.
Method of measurement
a) Set RF generator carrier frequency 130 MHz, modulating signal frequency 1 kHz,
internal amplitude modulation, modulation index 30% and output level 100 µV.
b) Set volume control key (AF GAIN) of the receiver on output power 50 mW, measure
RMS output voltage include noise uAF (audio frequency) on the oscilloscope (signal +
noise = S+N) and mark the value into all three lines in the table 1. Calculate the values
of noise uN (N) so that (S+N)/N are 6, 10, or 26 dB (use ratio from homework) and fill
the results in the tab.1.
c) Switch off the modulation. In this case the oscilloscope measures RMS level of noise
uN (N) that depends on the input RF signal level, but only if the time base of the
oscilloscope is adequately long (minimum 200 ms). Set lower input RF signal level
(but not lower than 0,4 µV) so that measured output noise level uN corresponds to
level calculated in b).
d) This RF signal level [µV] is the sensitivity for required (S+N)/N (in case the output
power level of the receiver is minimally 10% of standard power set in a) so 5 mW).
e) Measure the sensitivity for (S+N)/N = 10 dB and 26 dB by the same way.
f) Repeat the measurement for both side frequency of the band but only for (S+N)/N =
10 dB. Enter the results to tables 1 and 2.
Table 1: f = 130 MHz
(S+N)/N [dB]
6
10
26
uAF [mV]
uN [mV]
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Sensitivity [µV]
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5. BASIC PARAMETERS OF RADIO RECEIVER
Table 2: (S+N)/N = 10 dB
f [MHz]
uAF [mV]
130
137
117,975
uN [mV]
sensitivity [µV]
Task 2)
The receiver must often be capable of handling a wide range of signal power. In case
the input signal is weak the sensitivity and gain of the receiver have to be high. In case the
input signal is strong the gain has to be reduced to produce a nearly constant signal level at
the demodulator. This is accomplished automatically by the AGC circuit (AGC – Automatic
Gain Control).
AGC characteristics: According to RTCA standard audio output power shall not vary
more than 6 dB when the level of an RF input signal, modulated 30% at 1 kHz, is varied over
the range from 10 µV to 100 mV.
Method of measurement
a) Set attenuator 10 dB – (key ATT) to the input of the receiver.
b) Set RF generator to carrier frequency 130 MHz, standard amplitude modulation, and
output level 10 µV.
c) Set volume control in order not to exceed the output power 50 mW by changing the
input signal level in the range from 10 µV to 10 mV according table 3.
d) Measure RMS output voltage uAF and DC voltage UAGC on the output of AGC for
input levels uRF according to table 3 and enter the results to the table.
e) Explain in the conclusion of measurement whether the receiver meets the standard.
Table 3
uRF
uAF [mV]
UAGC [V]
10 µV
100 µV
1 mV
10 mV
100 mV
200 mV
Task 3)
AGC response time: When the level of an RF input signal, modulated 30% at 1 kHz,
is suddenly reduced from 200 mV to 10 µV, the receiver audio output shall, within 0,25 s,
return to and remain within 3 dB of the normal steady-state output obtained with an input of
10 µV.
Method of measurement
a) Set attenuator 10 dB – (key ATT) to the input of the receiver.
b) Set RF generator to carrier frequency 130 MHz, standard amplitude modulation and
output level 200 mV.
c) Set an oscilloscope to an appropriate amplitude and to a time base 400 ms.
d) Get ready for modification of the RF generator output level to 10 µV (instead of 200
write 10), push key SINGLE on the oscilloscope and speedily push the key µV on the
generator.
e) Read AGG response time by means of vertical cursors.
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5. BASIC PARAMETERS OF RADIO RECEIVER
Homework – shall be done before the measurement starts
• Calculate a voltage level ratio and a power level ratio matching with 3 dB, 6 dB, 10 dB and
26 dB fall. Enter the results to the table and apply them for the measurement.
dB
Ux / U0
Px / P0
-3
-6
- 10
- 26
Final questions – answers will be done after the measurement
1) Find out whether the sensitivity of the receiver meets the standard.
Manufacturer specification:
Measured value:
2) Find out whether the AGC characteristics and AGC response time meet the parameters
of airborne radio receivers.
Tab. 5: Technical parameters AR5000
Frequency range
10 kHz ~ 2600 MHz (minimum accepted frequency input 5 kHz)
Tuning
NCO 1Hz ~ 999.999999 kHz
Modes
AM, FM, USB, LSB & CW
I.F frequencies
1st I.F. 622.0 MHz, 2nd I.F. 10.7 MHz, 3rd I.F. 455 kHz
Standard fitted filters
3 kHz, 6 kHz, 15 kHz, 30 kHz, 110 kHz & 220 kHz (provision for 500 Hz option)
Memory channels
1000 (100 ch. x 10 banks)
Search banks
20 banks
Memory scan speed
25 channels per second in standard mode, 45 channels per second (max) in Cyber
Scan
Search speed
25 increments per second in standard mode, 45 increments per second (with step size
of 100 kHz or less) in Cyber Search
PASS frequencies
2100 total (21 banks x 100 ch. inc VFO)
Priority
1 channel
I.F. output
10.7 MHz with maximum ± 5 MHz bandwidth
External reference
10.0 MHz
Mute
Phono/RCA socket CMOS input pull-up to 5 V @ 100 kOHMS
Operating temp.
0 to + 50 C
Aerial input
50 OHM unbalanced N-TYPE & SO239
Audio output (13.5V)
1.7 WATT into 8 OHMS @ 10 % THD
Size
217(W) x 100(H) x 260(D) mm approx. excluding projection
Weight
3.5 kg
CPU 8bit
ROM 32 768 Byte, RAM 1 024 Byte
EEPROM
131 072 byte (1M Bit)
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5. BASIC PARAMETERS OF RADIO RECEIVER
Tab. 6: Selectivity [μV])
Receive frequency
10 dB S/N
AM 6 kHz
12 dB SINAD
SSB/CW 3 kHz
12 dB SINAD
FM 15 kHz
12 dB SINAD
FM 220 kHz
63.00
17.70
-
-
4.46
1.25
-
-
2.23
0.40
-
-
1.25
0.40
0.56
1.58
0.63
0.30
0.40
1.25
0.63
0.30
0.36
0.89
10kHz - 40kHz
40kHz -100kHz
100kHz – 2MHz
2 MHz – 40MHz
40MHz – 1,000MHz
1,000MHz – 2.6GHz
Tab. 7: IF filters bandwidth
Filter kHz
Total noise
bandtwidth kHz/dB
Total skirt
bandtwidth kHz/dB
0.5
0.5
-3
2.0
-60
3
2.4
-6
4.5
-60
6
9
-6
20
-50
15
15
-6
30
-50
30
30
-6
70
-50
110
140
-3
350
-20
220
260
-3
520
-20
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5. BASIC PARAMETERS OF RADIO RECEIVER
Obr. 3: Block diagram of communication receiver AOR AR 5000
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