The order of modeling of measurements and analysis of its results

DETECTION OF AMPLITUDE-MODULATED SIGNALS

Purpose of work: To learn the fundamental principles of amplitude-modulated signal detection, explore modes of amplitude-modulated signal detectors on the basis of bipolar transistor using modeling in program Electronics Workbench.

The order of modeling of measurements and analysis of its results

1. Explore amplitude collector detector.

1.1. To study the collector detector of AM-oscillation build scheme in accordance with Fig. 5.3. With key [0] disable the heterodyne.

1.2. Transmit on the base of bipolar transistor AM-signal with parameters: frequency of bearing oscillation f_b=2 kHz; frequency of modulation F_mod=4 Hz; modulation coefficient M=0,5; amplitude of bearing oscillation U_in.b according to a table 5.1.

Values of parameters control using oscilloscope

1.3. Measure the maximum U_out.max and minimal U_out.min values of output signal of the detector on collector of bipolar transistor. The measured values add to your table. 5.1. If the value U_{out. max} and U_{out. mon} a little differ from the constant component of signal U_{out 0},g, their deviation from the constant component should be measured using the oscilloscope AC mode.

Table 5.1

Uin.b, V									2,5
Uout.max, mV	-22.26	-26.75	-30.53	-32.84	-34.48	-35.57	7.59	2.47	0.291
Uout.min, mV	-29.05	-31.25	-33.12	-35.11	35.66	36.06	-5.6	-1.09	-0.256
Uout0, mV	-51.31	-29	-31.8	-33.9	-35.07	-35.8	0.9	0.69	17.24
Uout1, mV	3.4	2.35	1.3	1.08	0.59	0.245	6.6	1.78	0.274
Kdet	0.09	0.075	0.052	0.054	0.039	0.0245	1.32	0.712	219.44
Uout 0 theor LD, mV	-40	-10	-26.1	-29	-15.1	-30	0.81	0.5
Kdet.theor LD
Uout 0 theor KD, mV	-36	-8	-21	-26	-13	-26	0.63	0.42
Kdet. theor KD	0.125	0.125	0.125	0.125	0.125	0.125	0.125	0.125	0.125

1.4. From the measured values ​​determine:

- constant component of output signal

U_out0=(U_out.max+ U_{out min})/2 (5.6)

- amplitude of the variable component of output signal

U_out1=(U_out.max- U_{out min})/2 (5.7)

- detection coefficient

(5.8)

and put their values ​​to the table. 5.1.

1.5. Calculate the theoretical value:

- constant component of the linear output signal of detector using formula (5.1);

- coefficient of linear detection of detector using formula (5.2);

- constant component of output signal of quadratic detectors using (5.3);

- detection coefficient of quadratic detector using formula (5.5).

For calculation use the following approximation VAC of bipolar transistor:

- at a piece-wise linear approximation:

(5.9)

- at a power approximation:

Calculation results add to your table. 5.1.

1.6. Compare experimental and theoretical values ​​of output signal constant and detection coefficient of detector and make conclusions.

2. Explore the synchronous amplitude detector based on bipolar transistor.

2.1. For investigation of the synchronous detector of AM-oscillations in the circuit (Fig. 5.3) connect the heterodyne key [Q].

2.2. Transmit on the base of bipolar transistor AM-signal with parameters: frequency of bearing oscillation f_b=2 kHz; frequency of modulation F_mod=5 Hz; modulation coefficient M=0,5; amplitude of bearing oscillation U_in.b according to a table 5.1.

Values of parameters control using oscilloscope.

The signal parameters of heterodyne: oscillation frequency f _het = 2 kHz; phase of oscillations φ=0; effective voltage U_{het ­}according the table 5.2.

2.3. Measure the maximum _{Uout. max} and minimal U_out._min value of output signal of detector on the collector of bipolar transistor.

The measured values add to your table. 5.2.

Table 5.2

Uhet, mV
Uin.b, mV								2,5	2,5
Uout.max, mV	35.56	35.56	27.78	9.6	9.6	1.15	2.71	0.23	0.51
Uout.min, mV	-18.91	-21.46	-18.72	-4.26	-4.36	-3.195	-1.51	-0.217	-0.284
Uout 0, mV	8.3	7.05	4.53	2.67	2.62	0.5001	0.6	0.225	0.113
Uout 1, mV	27.23	28.51	23.25	6.93	6.98	4.01	2.11	0.225	0.398
Kdet	2.723	2.851	2.325	1.386	1.396	1.02	0.84	0.18	0.318
Uout 0 theor, mV	13.33	13.33	19.165	32.8	32.8	39.13	39.57	39.82	39.61
Kdet.theor

If the value of U_out.max and U_{out. min} differ a little from constant component of signal U_{out 0}, their deviation should be measured in AC oscilloscope mode.

2.4. According to the measured values ​​determined using the formulas (5.6) - (5.8): a constant component of output signal, the amplitude of the variable component of output signal, detection coefficient and put their values ​​to the table. 5.2.

2.5. Calculate the theoretical values: constant component of output signal of synchronous detector using formula (5.4) detection coefficient of synchronous detector using formula (5.5).

Fo calculation use average value S₁ = 1 A / V according to the approximation VAC of bipolar transistor (5.9).

The calculation results add to table. 5.2.

2.6. Compare the experimental and theoretical values ​​of constant component of output signal and detection coefficient of detector and make conclusions.

3. Explore the impact of phase shift φ between signal and oscillation on the output of heterodyne on the work of synchronous detector.

3.1. For investigation of the impact of phase shift φ on the work of synchronous detector, transmit on the base of bipolar transistor (Fig. 5.3) AM signal with the parameters: frequency of carrier oscillation f_c=2 kHz; modulation frequency F_m = 5 Hz; modulation coefficient M = 0.5; amplitude of carrier oscillation U_{in. c} - according to the table. 5.3.

The parameters of heterodyne signal: frequency of oscillations U_h = 2 kHz, phase of oscillations φ- according to the table. 5.3; effective voltage U_h - according to the table. 5.3.

Table 5.3

Φ, grad
Uh, mV
Uin. c, mV
Uout. max, mV	9.59	9.59	5.83	5.83	5.83	5.83	9.59	9.59	5.83
Uout. min, mV	-5.54	-4.16	-5.63	-4.35	-4.35	-4.35	-5.54	-5.54	-5.56
Uout 0, mV	2.025	2.715	0.1	0.74	0.74	2.04	2.025	2.025	2.025
Uout 1, mV	7.5	6.8	5.73	5.09	5.09	5.09	7.5	7.5	7.5
Kdet	1.5	1.36	1.146	1.018	1.018	1.018	1.5	1.5	1.5
Uout 0 theor, mV	32.81	32.81	35.63	35.63	35.63	35.63	32.81	32.81	35.63
Kdet. theor

3.2. Repeat measurement paragraphs 3.3-3.4 and their results add to your table 5.3.

3.3. Repeat calculations 3.5 and their results add to your table. 5.3.

3.4. Compare the experimental and theoretical values ​​of constant component of output signal and detection coefficient of detector and make conclusions.

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