Introduction
Contents
1. lt 60 dBc Spurious gt 200 KHz lt 80 dBc Pre emphasis Flat 50uS 75uS by jumpering Introduction 19KHz Pilot Tone Mono L R Stereo L R DSB Amplitude 20 15K 19K 23K 38K 53K Freq Hz Figure 1 Frequency spectrum of the composite signal Above shows the theoretical frequency spectrum of the stereo multiplex signal MPX signal The MONO signal on the far left goes from approx 20Hz to 15KHz and is used to transmit the sum of the left and right channel This assures compatibility with older MONO receivers that only receive this part of the spectrum Going from left to the right we stumble upon the 19KHz pilot just above the MONO signal This pilot has a couple of functions 1 It signals presence of the stereo signal by detecting it the receiver switches to stereo 2 It enables demodulation of the L R signal and LEFT RIGHT channel reconstruction The 19KHz signal is used to demodulate the DSB Double Side Suppressed Carrier signal stretching from 23KHz to 53KHz This signal contains the L R information difference between the left and right audio channel This is what the stereo encoder does to generate the Stereo Multiplex signal Revised by BG7CR on Nov 1 2012 Any question please send email to littleshirely gmail com Please visit our website http www 108MHz com for more products OPERATING amp MAINTENANCE INSTRUCTIONAL USER MANUAL FM STEREO ENCODER SE 1201 DRAFT Version12. FM STEREO ENCODER SE 1201 DRAFT Version1 1 Reminders 1 Heat will be produced during operation Pay attention to keep ventilation cooling 2 Connection wires should be as short as possible 3 good shielding measures should be adopted to avoid interference Revised by BG7CR on Nov 1 2012 Any question please send email to littleshirely gmail com Please visit our website http www 108MHz com for more products
3. 1 SOME FACTS ABOUT STEREO Even the best stereo encoder is by itself not enough to guarantee good channel separation at the receiving side over the whole audio frequency range Many factors are involved 1 THE TRANSMITTER The first problem usually occurs at the transmitter Badly designed audio stages of the modulator will produce low frequency phase shifts affecting separation But the main problem is the phase locked loop section of the transmitter PLL tries to correct the frequency deviations caused by the audio effectively canceling modulation The frequency correcting signal is passed through a low pass filter loop filter This loop filter dampens smoothes and averages the correcting pulses from the PLL circuit before passing the corrected voltage to the frequency control part of the modulator The loop filter is usually the cause of the phase shifts due to not being able to sufficiently dampen and smooth the correcting pulses when the transmitter is fed with low frequencies Variable frequency oscillators do not suffer from the problem at all due to no frequency correcting circuits PLL In short a badly designed transmitter can be hugely detrimental to the stereo signal created by stereo encoder Do not jump to the conclusion that the stereo sound that you are listening to is the stereo encoder only 2 THE RECEIVER Filter Bandwidth and Stereo Decoder of receiver Even if the transmitter adds no phase shifts to the multiplex sign
4. DRAFT Version1 1 RIGOL STOP haw Ronnie f O 6 00 v eo RSE AMAL nti INN 1 l Mi AALE T Ta ni j i THAN ARMA TARIVY WA Wi RIGOL STOR ARRAS FIO 6 000 Rift lt SHz i yy il i Ver 6 24 mi 1 66 Ni Time 200 0us UPO 00GOS Test Point MPX OUT LEFT 1KHz RIGHT None Pilot Off Test Point MPX OUT LEFT 1KHz RIGHT None Pilot On The waveform near the middle axis is the 19KHz Pilot Its amplitude could be adjust by W4 Revised by BG7CR on Nov 1 2012 Any question please send email to littleshirely gmail com Please visit our website http www 108MHz com for more products OPERATING amp MAINTENANCE INSTRUCTIONAL USER MANUAL FM STEREO ENCODER SE 1201 DRAFT Version1 1 RIGOL STOP mannna n F amp 6 00 Y cnt es Test Point MPX OUT LEFT 1KHz 1 5Vp p ly y 1 T i RIGHT 1KHz 1 5Vp p i Pilot On i i j N Wy ww Ver D 5 720 LA i GEE 1 00 Time 200 0us GO G000s RIGOL STOP OCU Enan F 60o 9 Test Point MPX OUT LEFT 1KHz RIGHT 1 5KHz pilot off AAT Ti A j Y i be 1 60 Time 200 Qus UHA 00H RIGOL ETOR Sa a CS 6 oow Y ese Test Point MPX OUT LEFT 1KHz 1 5Vp p mn iia 20 Eai T m W Revised by BG7CR on Nov 1 2012 Any question please send email to littleshirely gmail com Please visit our website http www 108MHz com for more products OPERATING amp MAINTENANCE INSTRUCTI
5. ONAL USER MANUAL FM STEREO ENCODER SE 1201 DRAFT Version1 1 Functional Diagrams 19KHz Pilot yE 864Mhz 4 Buljdwes xg LF WwW 5 aA Y W7 Pre emphasis gt gt 1 L IN MPX OUT Mm EMH Revised by BG7CR on Nov 1 2012 Any question please send email to littleshirely gmail com Please visit our website http www 108MHz com for more products OPERATING amp MAINTENANCE INSTRUCTIONAL USER MANUAL FM STEREO ENCODER SE 1201 DRAFT Version1 1 MPX LPF Audio Input LPF Pr eEmphasis 19KHz Pilot Gener ator 8x Over Sampling Audio Input LPF Pr eEmphasis 1 5M Clock Clock Generator DC Regulator Installation BASEBAND MPX IN OUT REMOT d M e LEFT MONO LEVEL RIGHT LEVEL PaA ale iE a ca Ee LINE OUT ell i J N LL MIXER N x O a O a x o OF OSO OLO ogee OSOS s 5 5 5 o O O O A O O O O O O IZ OSOL O05 OL62 CY O DC12V O LY Q O O O O OKOA OKO ORO ORO O O oo O oe O O C C Power supply CG AANI OXOXO OOO OXOXO O O O O OS se 5 26 26 O re 5S Revised by BG7CR on Nov 1 2012 Any question please send email to littleshirely gmail com Please visit our website http www 108MHz com for more products OPERATING amp MAINTENANCE INSTRUCTIONAL USER MANUAL
6. OPERATING amp MAINTENANCE INSTRUCTIONAL USER MANUAL FM STEREO ENCODER SE 1201 DRAFT Version1 1 STEREO ENCODER a lt REV 11 4 8078Q 201206 http sw 106 Hz com a Introduction Are you still using single chip FM stereo encoder scheme One chip integrated audio process stereo encoder frequency synthesis modulation and a series of other functions It seems is a simple and cheap solution Though such kind of chip can implement relevant function its performance can not be guaranteed due to its design orientation and cost control In principle it only can be used on mobile phone PDA and such similar low power portable devices Such kinds of chips are typically known as ROHM series BH1415 BH1417 BH1414K and BU2682 etc S147xx series of SILICON LABS and KT0801 of KT Micro etc SE 1201 is a comprehensive scheme based on performances and costs It is a high specification stereo encoder Designed for optimum stereo separation and excellent spectral cleanliness this encoder will provide that extra performance for radio stations who want something a little special We searched and analyzed such relative encoder product materials that we can find except those very professional ones of course the circuit is also pretty complex there are only very few schemes We do not use matrix code method to design this encoder any more but use lots of switching mode However most of the materials we found are defective even are wrong S
7. OPERATING amp MAINTENANCE INSTRUCTIONAL USER MANUAL FM STEREO ENCODER SE 1201 DRAFT Version1 1 VCC VCC Ls ib wees KE h S RIGOL STOP ABI f OB GOANV Test Point TP5 y kmt MSSHZ This is the waveform of 19KHz pilot tone It is precise P a ZN oa ee FON f 4 synthesizing The phase must f synchronizes with sub carrier Bett i 38 kHz f ad YS bE 166m Time 16 08us GO 0000s 2 Stereo Generator Section Switching mode encoder is divided into hard and soft switch mode Because subcarrier of hard switching mode outputs rectangular wave these composite signals contains three times and more harmonic sidebands still need low frequency filter to eliminate On 99 KHz has a certain amount of low pass filter attenuation produced by the nonlinear phase shift to baseband sideband 53 KHz will still have great influence on it still needs to add phase compensation circuit or separating degree index is not high lt 50 dB even if added phase compensation circuit also be very difficult and soft switch mode subcarrier not rectangle wave but close to cosine wave does not exist the problems which can put the separating degree do high gt 60 dB Revised by BG7CR on Nov 1 2012 Any question please send email to littleshirely gmail com Please visit our website http www 108MHz com for more products OPERATING amp MAINTENANCE INSTRUCTIONAL USER MANUAL FM STEREO ENCODER SE 1201
8. al transmitted the receiver radio at the listening end can still cause trouble The filters in the radio can cause phase shifts to the multiplex if too narrow in bandwidth Many cheaper tuners have less filtering less manufacturing cost which although not great for selectivity provides for excellent separation in strong signal environments The above is only true if the stereo decoder in the radio or tuner is ok It is very hard to obtain any modern stereo decoder chips that give more than 45 dB of separation some give only 35 dB So even with modern day DSP digital signal processor stereo encoders that achieve separations of more than 70 dB you will never hear it because the radio you will be listening to it on may only allow 45 dB at best As you see stereo is not just about a stereo encoder Circuit Description 1 19kHz Pilot Tone Generator Section The 19KHz pilot tone comprises a baseband signal and the L R and L R signals consist of DSBSC double sideband suppressed carrier modulation centered at 38 kHz For a receiver to correctly demodulate the signal the transmitted pilot tone and L R signal must synchronize at their respective zero crossings In addition any distortion in the pilot tone produces harmonics that can interfere with adjacent sections of the signal Revised by BG7CR on Nov 1 2012 Any question please send email to littleshirely gmail com Please visit our website http www 108MHz com for more products
9. ome circuits which claims using microcomputer control circuit which its chip actually used just to produce the most basic pulse a CD4060 chips is enough Before illustrating how SE1201 FM stereo encoder works we should make some basic principles clear firstly We did many experiments and found it is very difficult to make an excellent encoder under normal circumstances You will need a lot of professional equipments such as the signal generator oscilloscope TRMS voltmeter frequency counter receiver and modulation analyzer etc Of course if you have a FMAB of R amp S it will become easier In addition considerable experience and expertise are required if you want to produce such an encoder So we made this encoder and hope you will learn a lot from it and enjoy it Revised by BG7CR on Nov 1 2012 Any question please send email to littleshirely gmail com Please visit our website http www 108MHz com for more products OPERATING amp MAINTENANCE INSTRUCTIONAL USER MANUAL FM STEREO ENCODER SE 1201 DRAFT Version1 1 Specifications gt 55 dB 50 Hz 15 kHz typically 60 70 dB 0 5 dB 20 Hz 15 kHz Stereo separation Frequency response Pilot frequency 19 KHz 2 Hz Pilot level 10 38 KHz rejection gt 65 dB IMD and beats Input level Input impedance Output level Output impedance Spurious gt 100 KHz gt 60 dB no clipping O dBm 775 mVrms 2 2 Vp p for 75 KHz adjustable 5k Ohms unbalanced 0 dBm 75 Ohms
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