Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

Author: Les Hadley

value of the capacitance across Pins 12 and 13. In this particular example, the transmitter operates at 14.3MHz with the VCO set to 26.6MHz.

SYSTEM OPERATION SUMMARY

The slope of the VCO transfer function is termed KO and is The purpose of the fiber Iink is to transmit broadband video and measured in radians per second per volt or simply Herz per volt.

sound over moderate distances (2.5km) with existing low cost Thus, to obtain the magnitude of the differential voltage for a given components and minimal complexity.

frequency deviation the relationship below is used: Figure 1 depicts a complete system implementation. The MHz

application makes use of a very wideband VCO to generate an FM

V

f

D(voltsDC)

k

MHzV

modulated carrier at 28.6MHz followed by a fast TTL LED driver to O

emit saturated 850nm light signals for entry in to the glass fiber. A I

Constant

B2

PlN diode receiver is coupled to a 140MHz bandwidth transimpedance preamplifier for increasing the detected signal KO is dependent upon the control bias generator current at Pin 2 as amplitude and then fed to a phase-locked loop demodulator for is noted from the graph. Higher current into Pin 2 results in a higher recovering the original modulation signals.

conversion gain, KO. For a center frequency of 1MHz and an 800µA bias current into Pin 2, K

The wideband FM sound subcarrier (150kHz deviation) is summed O is 1.7MHz/V across Pins 4 and 5

(V

with baseband video at 10.7MHz and transmitted at a reduced level O).

relative to the 3.58MHz color reference signal. Cross modulation The value of KO also increases linearity with center frequency so between sound and picture information is minimized in this way. FM

that at 30MHz KO becomes 30X 1.7 or 51MHz/V. Note that in this demodulation of the sound subcarrier is accomplished after passing application the bias current is set at 320µA; that is the device is through an IF gain block by a quadrature-type phase discriminator.

sinking current into Pin 2. This lowers KO below the given value for The present sound circuit does not automatically frequency-lock to 800µA shown on the graph in Figure 3 and requires a higher the transmitted subcarrier, but is fixed-tuned to 10.7MHz. A tracking number of V/MHz to modulate the VCO. The signal to the VCO is PLL sound demodulator could be used to eliminate drift problems DC coupled from the differential output of the NE592 in order to between transmitted sound subcarrier and the receiver in future preserve bandwidth and to maintain proper biasing relative to the designs.

NE564.

Setting FM Deviation

SYSTEM DESCRIPTION AND OPERATION

In order to calculate the approximate frequency deviation, a linear relationship between ∆K

Transmitter Unit: Video Channel

O and ∆IB2 is assumed. The value of KO

for a Pin 2 bias of 320µA is determined by the following relationship: The transmitter circuit consists of a wideband differential amplifier (NE592), a VCO (NE564) and an LED driver, the NE522 high speed

comparator (see Figure 2) The video signal is AC coupled into the k

(1.7 0.95) 320 0.95 MHzVolt O

2 800

modulator preamplifier and followed by a sync tip clamp to provide DC restoration of the composite video signal and to prevent variation

= 1.1MHz/V@1MHz

of modulation deviation with varying picture content. (A complete

= 33MHz/V@30MHz

video clamp and sync processor may be designed using the TDA9045 and TDA2595 combination. This particular application was The measured differential voltage between Pins 4 and 5 for normal not tested at the time of this publication.) operating signal levels and standard NTSC color bars transmitted is 80mV

A video signal level of 250 to 300mV peak is required to maintain P-P. The estimated total deviation is then 1.3MHz. This results in a Video channel bandwidth for the 3.58MHz color signal of optimum picture modulation. Since there is no AGC circuit in this approximately:

particular design, this is a critical parameter and must be con- trolled to prevent over-modulation and picture degradation. Addition of an

= 2(1.3 + 3.58)MHz

AGC using the above-mentioned parts would be a definite

= 9.8MHz

improvement for varying input level video. Using the present limited design, however, -10dB of attenuation was used with a 1V peak This is rather a small deviation for wideband video transmission and NTSC signal source at 75Ω. This is the common level available the decision was made to use the 2nd harmonic of the fundamental from most standard video signal systems.

VCO frequency to obtain twice the deviation. The VCO modulator is then set at an I

Frequency compensation (pre-emphasis) is inserted in the form of a B of 320µA which provides sufficient 2nd harmonic content for this to operate successfully. This is shown in Figure 5

passive RC lead network at the Pin 14 input to the NE592

with the fundamental at 14.3MHz with the middle spectral plot differential amplifier. This compensates for degenerative frequency showing required 28.6MHz carrier harmonic with improved deviation distortion and provides better color balance in transmission.

ratio.

The main FM modulator consists of an NE564 used only as a linear wideband VCO. The other sections of the device are not used.

Total FM Signal Bandwidth

Differential DC coupling to the VCO terminals is attained via the loop For a total video bandwidth of 4.2MHz the transmission bandwidth filter terminals, Pins 4 and 5. The NE564 VCO is designed as a is:

differential current controlled balanced multivibrator. It possesses an BW = 2x2(1.3 + 4.2) = 22MHz

extremely linear transfer function as illustrated in Figure 3. The Note that a bandpass filter could be installed in the signal path graph shows how the VCO frequency varies with applied DC voltage between the NE592 preamp/buffer to reduce noise bandwidth, but across Pins 4 and 5. The VCO center frequency is determined by February 1993

1

Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

this improvement was not tried. Adequate signal space for the NE5750 output on Pin14. The pot. R7, provides the calibration baseband video and the 10.7MHz subcarrier would be 11MHz.

adjustment for maximum 10.7MHz deviation.

(Filter characteristics must provide good differential gain and phase The actual 10.7MHz level to the 30MHz modulator is set by pot R6

response.)

and is adjusted by monitoring the spectral level at the output, Pin 9, A second bandpass filter could be added in the path between the of the NE564 with a spectrum analyzer. The relative sound carrier modulator and the LED driver stage (22MHz bandwidth). This would (lower 28.6MHz sideband) is set approximately 20dB below the improve the overall video signal-to-noise ratio.

3.58MHz color reference signal. This is accomplished by first noting the sideband level of the video information (Figure 5), removing the The NE592 is biased with +5V and -1.8V to achieve the critical video modulation and setting the 10.7MHz level with R8 on the dynamic swing to properly slew the VCO over the required range sound modulator board.

without sacrificing faithful waveform reproduction in the transformation to linear FM modulation. Video signals contain both The Receiver Unit

very low and high frequencies which are transient and phase Light energy from the fiber optic cable is fed to the BPF24 PIN diode sensitive. The unused input pins to the phase detector, Pins 6 and 7

and transformed to a small current typically in the 1 to 5µA range.

bypassed to ground. Pin 3 is grounded.

This photodiode current carries all of the FM carrier information in The 28.6MHz FM signal from the NE564 is taken from the Pin 9

the signal bandwidth of approximately 22MHz centered at 28.6MHz.

open collector VCO output port which requires a 470Ω pull-up The photo- current is now amplified and transformed into a resistor to 5V. A100Ω resistor is added to Pin 11 to improve the fall differential signal voltage by the NE5212 transimpedance amplifier time of the output waveform. The signal is then fed into the NE522

(Pin 1 input). In this particular application, however, the output is not (74F3040) high speed comparator where a threshold level is set up used differentially, but a single-ended signal is taken from Pin 5 of on the inverting terminal to provide duty cycle adjustment and noise the NE5212 and AC coupled to Pin 6 of the NE564.

threshold. The NE522 has an open collector output which lends The NE5212 has a differential transresistance of 14k. This itself easily to driving the LED transmitter diode (CQF24); the translates to 14µV/mA of input current, yielding 35mV of differential 74F3040 has a source-sink output stage which requires that the output voltage for 2.5µA input current. Since the device is used LED be connected as shown in Figure 2a.

single ended, only half, or 17.5mV, output is available to drive the The CQF24 generates 100µW of 850nm optical energy with a phase detector of the NE564. (See Figure 12 for actual output typical rise and fall time of 10ns. It is rated at 250mW dissipation signal from NE5212). The low signal level input to the PLL makes it and 100mA continuous current.

necessary to run the gain setting bias at a higher level than usual; this, in addition to the wide bandwidth, requires a bias current of Spectral frequency plots taken under normal operating conditions 2.2mA sinking into Pin 2 of the NE564. Another modification to the with NTSC color bar signal input for the sections of the transmitter nominal NE564 operating conditions is the choice of a higher supply described above appear in Figures 4 through 6.

voltage on the phase detector portion of the device (+8V on Pin 1) to increase the linearity and dynamic range for fast video signals. The The Sound Channel

As shown in the block diagram in Figure 2, audio input is fed VCO section is supplied from +8V through a 200Ω dropping resistor through a 2:1 compressor which consist of the NE575 low voltage and operates on 4.5V at Pin 10. (Note that the absolute maximum compandor. This device compresses all audio signals according to voltages for the phase detector and VCO are 14 and 6V, the transfer function shown in Figure 7. It is required to limit the respectively).

peak FM deviation for the10.7MHz VCO to +75kHz for 0dBV input VCO Frequency Adjustment

(1VIN 600Ω RMS). Audio compression also improves intelligibility in The NE564 receiver PLL is operated at the same frequency as the systems with limited signal-to-noise ratio. This device, NE575, 2nd harmonic of the transmitter fundamental 28.6MHz. Prior to operates at unity gain for an input level of 100mVRMS audio input making any adjustments, the bias current to Pi n 2 is set to 2.2mA.

which is 0dB for the NE575. The 2:1 compression factor refers to The spectrum of the receiver VCO without a fiber link signal, fiber the AC signal level in dB above or below 100mVRMS.2 Output from disconnected, is shown in Figure 13. When making the initial the NE575 is fed to the second NE564 modulator with a VCO center center frequency adjustment to the VCO trimmer cap (NE564 Pin frequency set at 10.7MHz. Refer to Figure 8 for typical circuit 12, 13, 2-20pF) the fiber cable is disconnected. (Note that a thermal diagram. The 10.7MHz subcarrier is fed to the NE592 for summing stabilization time of 1 hour is recommended prior to any transmitter with the main baseband video signal. The level of the sound or receiver calibration adjustments.) subcarrier is adjusted to a level 20dB below the 3.58MHz color video sideband (28.6MHz signal) by adjustment of the output level With the link connected and a proper signal present at the input to potentiometer at the emitter follower, Q1 (see Figure 9). This can the NE554 Pin 5, the PLL will lock onto and track the incoming be accomplished most easily by monitoring the combined 28.6MHz wideband FM signal. (See Figure 14 for VCO spectrum.) Note that signal from the main modulator (Pin 9 NE564) using a spectrum the unwanted harmonic signals number one and three have not analyzer. The 10.7MHz carrier deviation is adjusted using 0dBm been filtered out in this application example.

(775mVRMS into 600Ω) input to the compressor at 1kHz and The demodulated baseband video plus 10.7MHz signal then adjusting the deviation with the input potentiometer, R7, which feeds appears on the analog output port, Pin14. A wideband amplifier with the NE564 (see Figure 9 for the 10.7MHz schematic). Figure 10

low differential gain and phase error (NE5539) is used to boost the displays the proper frequency deviation spectrum as set by the R7

combined signal with the composite video level raised to 1V peak adjustment. A 0dBm (775mV) input to the compressor is 16dB

into 7Ω. The actual measured value of the video using an NTSC

above the compandor 100mV reference level and the compressor color bar signal is 1VP-P on the output port. The NE554 output to will reduce this +18dB input level to approximately 260mVRMS at the the NE564 from Pin14 is 250mVP-P.

February 1993

2

Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

Figure 15 shows the composite baseband video plus 10.7MHz The audio amplifier and control section shown in Figure 1 is not subcarrier spectrum.

included in this application note. For further detail on the audio portion and applications examples, please refer to Section 7 of the The final stage of the video channel is the NE5539 which drives Philips Semiconductors IC-11: General-Purpose Linear ICs.

directly into the video monitor. Biasing the DC offset of the postamplifier is necessary to prevent sync distortion and optimum Suggested areas of improvement are: 1. The addition of bandpass video response. This is accomplished by adjusting R2 (1MΩ pot on filters to improve transmitter and receiver signal-to-noise; 2. Video Pin 1 of NE5539) for 0V average at the output. Note that a lead-lag sync tip or black level clamp with AGC at transmitter modulation network is connected across Pins 1 and 14 to stabilize the op amp input; 3. Addition of an AGC stage after the receiver transimpedance which has a closed loop bandwidth of approximately100MHz for a amplifier to improve optical path dynamic range.

closed loop gain of 4. This excessive bandwidth creates noise in Power Supply Requirements

the picture information and is reduced by the 20pF capacitor from Pin 12 to 14. (See Figure 11.)

The regulated voltages required to operate the system are as follows:

Sound Channel Operation and Adjustment

+5.00V

A portion of the output signal from the NE5539 is also sent to the NE604A to be amplified and demodulated (see Figure 5).

-5.00V

The composite signal contains both the video and the 10.7MHz

+8.00V

subcarrier. A ceramic 10.7MHz bandpass filter is used before the NE604A to remove all but the subcarrier. The NE604A contains a

-8.00V

high gain IF amplifier and an LC quadrature detector for Test Equipment

demodulating the FM sound Information.

1. HP8568B Spectrum Analyzer

Adjustment of the sound channel Is carried out after the system has 2. Tektronix PC6202 FET Probe 10X

been on for one hour to allow thermal stabilization. A 1kHz test 3. Philips 5510 Color Generator

signal is injected into the audio input port of the NE575 compressor board and set to 775mV

Footnotes

RMS terminated in 600Ω. Using a spectrum analyzer adjust R7 while observing the 10.7MHz output on a 1. Philips Semiconductors Linear Data Manual, Volume 1, Commu-spectrum analyzer and set the deviation for 150kHZ maximum. At nications, 1987

this point make sure that the 10.7MHz VCO (NE564) is on 2. Ibid.

frequency, and make any trim adjustments to the VCO trim REFERENCES

capacitor. Finally adjust R8 for a carrier amplitude by monitoring the Roden, Martin S., Analog and Digital Communications Systems, 2nd output of the transmitter VCO lower sideband, and set the10.7MHz Edition; Prentice Hall, 1985.

signal 20dB below the 3.58MHz sideband relative to 28.6MHz. The Philips Semiconductors, Linear Data Manual, Volume 1, last adjustment is the setting of the quadrature coil on the NE604A Communications, 1987.

demodulator for maximum sound with the best signal-to-noise.

1. AN140:

Compensation Techniques for

(Refer to Figure 17 for the input signal spectrum to the NE604A.) Use with the NE/SE5539

2. AN175:

Automatic Level Control: NE572

CONCLUSION

3. AN176:

Compandor Cookbook

The system example described Is capable of transmitting single 4. AN179:

Circuit Description of the NE564

channel color video and sound transmission at 850nm with glass or 5. AN1991: Audio Decibel Level Detector plastic fiber optic cable of >2.5km. Signal transmission is of with Meter Drive (NE604)

adequate quality for Industrial inspection, security and other Philips Semiconductors, Linear Data Manual, Volume 3, applications of this limited nature. The most notable feature is its Communications, 1987.

minimal cost. It Is not meant to be used in broadcast quality environments. The user Is invited to make improvements and AN146;

Wideband FM Composite Video

alterations to the system to attain greater stability and higher quality.

Fiber Optic Link, Philips Semiconductors 1985

February 1993

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Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

+V

0V

COMPOSITE

VIDEO

28.6MHz

BANDPASS

VIDEO

OPTICAL

WIDEBAND

FILTER

AMPLIFIER

MODULATOR

CQF24

FM

INPUT

(NE592)

(NE522)

MODULATOR

(NE564)

ALTERNATE

74F3040

10.7MHz

(1/2)

SYNC

SOUND

TIP

SUBCARRIER

NE575

DC

FM

COMPRESSOR

CLAMP

MODULATOR

2:1

(NE564)

VIDEO

INPUT

OPTICAL INTERFACE FIBER

+V

BPF24

VIDEO

28.6MHz

GAIN = 4

FIBER INPUT

TRANSIMPEDANCE

PLL

BUFFER

850nm

AMP

DEMODULATOR

AMP

(NE5212)

(NE564)

(NE5539)

75Ω

OUTPUT

BANDPASS

FILTER

10.7MHz

L

10.7MHz

SOUND IF

AUDIO

DETECTOR

CARRIER

AMPLIFIER

(NE604A)

DET.

TDA1521

LED

SPEAKER

R

+V

DC

VOLUME

CONTROL

TONE

CONTROL

BALANCE

CONTROL

Figure 1. Video Fiber Transmission System February 1993

4

Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

5V

GAIN

ADJUST

5V

10k

2k

0.1µF

2

1

10

100Ω

470Ω

BIAS

0V

5V

0V

11

500pF

MICA

5

14

6

75pF

100Ω

4

NE522

DC

1k

5

10

9

1

CQF24

SYNC TIP

+

CLAMP

560Ω

3

47µF

1k

12

*A

8

10pF

COMPOSITE

NE592

VIDEO

VCO

IN

2-20pF

10kΩ

7

2

–

4

13

12

5

1

1k

P.D.

13

500pF

INPUTS

PRE-

NE564

–1.8V

EMPHASIS

COMP

10.7MHz

7

1k

2.3k

470Ω

6

3

ALC

SOUND

+5V

575

MOD

R

–5V

S

1k

(564)

500pF

0.1µF

0.1µF

75Ω

DEV = 75kHz

–5V

AUDIO

IN

28.6MHz

DEV = ±10MHz

5V

11

VCC

91Ω

12, 13

10

13Ω

7.5Ω

6

15

74F3040

8

B

14

7

74F3040

2

180pF

A

TTL IN

CQF24

1

*A

Figure 2a. LED Driver

*NOTE: An alternate LED driver which uses the 74F3040 line driver was incorporated in this particular application example. The 74F3040 has a higher current rating, but not the variable threshold capabilities of the NE522. The LED diode is operated in the saturated on-off mode for best signal-to-noise.

Figure 2. Fiber Optic Transmitter Block Diagram February 1993

5

Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

1.6

1.4

1.2

–400

–200

1.0

200

400

600

800

.8

.6

Figure 3. NE564 VCO Transfer Function, KO

MKR 3.58MHz

MKR 28.64MHz

REF –8.8dBm

ATTEN 10dB

–67.80dBm

REF –8.8dBm

ATTEN 10dB

–29.60dBm

10dB/div

10dB/div

START 10.4500MHz

STOP

12.08MHz

START 8.72MHz

STOP

48.72MHz

RES BW 100kHz

VBW 1kHz

SWP 1.0 sec

RES BW 300kHz

VBW 100kHz

SWP 20ms

Figure 5. Transmitter PLL Output with NTSC Color Bar Test Figure 4. NE592 Output Signal NTSC Video Plus 10.7MHz Pattern Input (Input Video –10dB Attenuation Below 1V Peak) Subcarrier (Probe 10X ATTN)

(10X FET Probe at Pin 9 NE564)

February 1993

6

Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

MKR 28.64MHz

REF –8.8dBm

ATTEN 10dB

–33.70dBm

10dB/div

1/2

2

REL LEVEL ABS LEVEL

V RMS

COMPRESSION

EXPANDOR

dB

dBm

IN

OUT

INPUT TO G

3.0V

∆

AND RECT

+29.54 +11.76

547.6mV

_14.77

–3.00

400mV

+12.0

–5.78

100mV

0.0 –17.78

10mV

–20 –37.78

1mV

–40 –57.78

100µV

–60 –77.78

START 23.02MHz

STOP

35.02MHz

10µV

–80 –97.78

RES BW 100kHz

VBW 300kHz

SWP 150ms

Figure 6. Transmitter LED Drive Spectrum with 10.7MHz Sound Subcarrier and NTSC Video Test Signal Input (10x ATTN) Figure 7. NE575 Compressor Transfer Function 0.1µF

VCC +5V

C15

GND

1

+

20

NE575

10µF

VCC

VIN

+

VOUT

2

+

–

19

C14

R13

R4

OP AMP

200

C3

V

10k

OUT

3

–

18

+

R10

10µF

OP AMP

R5

200

VREF

100k

4

17

3.9k

C11

C10

R9

GND

10µF

+

+

100k

5

16

4.7µF

+

CRECT

3.9k

2.2µF

Σ

CRECT

6

15

GND

+

2.2µF

GND

C6

Σ

7

14

VIN

10k

+

10µF

V

8

V

REF

REF

13

R8

10k

30k

+

R7

9

∆G

12

+

10k

30k

1µF

C8

10

∆G

11

10k

GND

GND

GND

GND

Figure 8. Block Diagram

February 1993

7

Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

+5V

FROM NE575

C2

COMPRESSOR

R1

C4

J1

C3

8.2k

µ

0.1 F

500pF

RCA

µ

µ

0.1 F

4.7 F

MICA

DEVIATION ADJ.

2

1

10

NE564

C7

R3

4

R2

10k

820

C6

R7

µ

4.7 F

µ

0.1 F

1k

Q1

R4

PD

3904

10k

9

5

C5

J2

µ

VCO

R5

0.01 F

RCA

100k

6

R8

11

10.7MHz

R6

1k

7

1k

500pF

C8

TANT

8

3

12

13

C9

TO NE592

C11

µ

0.1 F CER

MAIN MODULATOR

20pF

+ 5% MICA

C10

C12

1–10pF MINI TRIMMER

Figure 9. 10.7MHz Modulator

MKR 10.7000MHz

REF .0dBm

ATTEN 10dB

–49.30dBm

10dB/div

START 10.4500MHz

STOP

10.9500MHz

RES BW 10kHz

VBW 3kHz

SWP 75ms

Figure 10. 10.7MHz Sound Subcarrier PLL Output with 1kHz Input After Compression (Probe 10x ATTN) February 1993

8

Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

.01µF

+8V

.01µF

.47µF

200Ω

–8V

1k

R1

10Ω

0.1µF

+8V

10k

10Ω

.01µF

GAIN

OUTPUT

ADJUST

2

1

1.0M

100Ω

10

OFFSET

.01µF

0.1µF

ADJUST

7

NE564

.01µF

BPF24

BIAS

1M

47µF

+5V

1k

14

1

A

.01µF

6

10

150k

33Ω

12

2

λ

150Ω

850nm

4

1

28.6MHz FM

3

5

39pF

75Ω

VCO

5pF

8

NE5212A

NE5539

8

2–20pF

39pF

5

7

VIDEO OUT

6

.01µF

4

13

1VPK + 10.7MHZ

3

SOUND

14

SUB-CARRIER

@-20dB

12

NC

3k

3

+5V

9

470Ω

0.1µF

1k

1.5pF

Figure 11. 28.6MHz Receiver Block Diagram MKR 28.88MHz

MKR 28.72MHz

REF .0dBm

ATTEN 10dB

–83.40dBm

REF –8.8dBm

ATTEN 10dB

–17.70dBm

10dB/div

10dB/div

START 18.50MHz

STOP

38.09kHz

RES BW 300kHz

VBW 100kHz

SWP 20ms

START 22.64MHz

STOP

34.64MHz

RES BW 100kHz

VBW 30kHz

SWP 75ms

Figure 12. Receiver NE5212 Output at 28.6MHz with NTSC

Figure 13. Receiver PLL Spectrum Frequency with Color Bars and 5km Optical Attenuation (Probe 10x ATTN) No Signal from Fiber (Probe 10x ATTN) February 1993

9

Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

MKR 28.88MHz

MKR 3.58MHz

REF .0dBm

ATTEN 10dB

–48.00dBm

REF –8.8dBm

ATTEN 10dB

–17.90dBm

10dB/div

10dB/div

START 18.50MHz

STOP

38.09kHz

RES BW 300kHz

VBW 100kHz

SWP 20ms

START 580kHz

STOP

12.08MHz

RES BW 100kHz

VBW 1kHz

SWP 1.0 sec

Figure 14. 28.6MHz Receiver PLL VCO Spectrum with Link Figure 15. NE5539 Postamplifier Spectrum Baseband Phase-Locked and 5km Optical Attenuation (Probe 10x ATTN) Video and 10.7MHz Subcarrier (Probe 10x ATTN) 10.7MHz

CERAMIC FILTER

14

12

9

8

300Ω

.01µF

FM

10.7MHz

AUDIO

DISC

CERAMIC BP FILTER

OUT

16

6

.01µF

FROM MAIN

FM DEMODULATED

SIGNAL

NE604A

2

0dB

–20dB

0

3.58

10.7

fMHz

Figure 16. FM Demodulator

February 1993

10

Philips Semiconductors Data Communications Products Application note

A phase locked fiber optic system using FM modulation AN1434

MKR 10.7010MHz

REF .0dBm

ATTEN 10dB

–91.30dBm

10dB/div

START 10.3888MHz

STOP

11.0888MHz

RES BW 3kHz

VBW 3kHz

SWP 5.0 sec

Figure 17. 10.7MHz Recovered Signal Input to FM IF

Amplifier/Discriminator NE604A (Probe 10x ATTN) February 1993

11