pllplus

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PLL PLUS FM EXCITER MODULE

BW BROADCAST

The BW broadcast PLL+ is a compact FM broadcast exciter module with specications that puts many

commercial exciters to shame. The modern innovative design allows audio and RF perormance

never beore seen in module exciters. The virtual VFO dual loop system allows perect audio fatness

to below 10 Hz making AFC bounce and modulator overshoot a thing o the past. You now can pass

that low bass without distortion and get that perect stereo separation that you have been demand-

ing rom your exciter. Broadband No-Tune operation allows or simple use. The only adjustment

required is o the direct reading decimal dial switches or requency selection. RF power is muted dur-

ing out o lock conditions and the built in harmonic lter keeps your signal clean. The expansion con-

nector allows or external modules to be connected to the board such as the BW Broadcast PLL+ LCD.

Features

Phase locked loop system

Dual speed PLL

Low noise oscillator

Broadband design

No-Tune operation

Direct read switches

Very low distortion

Switchable pre-emphasis1 Watt output

Harmonic lter

Expansion connector

Compact size

Black oxide high grade PCB

Power output

Power requirementsHarmonic output

Spurious output

Frequency steps

Out o lock RF power down

Freq. stability

Audio input level

Freq. response

S.N.R.

Distortion

Pre-emphasis

1000mW +/- 100mW, 50 Ohms

15Vdc 300mAtyp 60dBc

typ >85dBc

12.5kHz steps

-50dBc

+/- 200Hz

adjustable

10Hz-100kHz

>80dB

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Principles o Phase Locked Loop systems

The Voltage controlled oscillator (VCO) eeds a portion o its RF into one side o a phase locked loop

chip. The other side o the PLL chip is ed with a reerence requency usually derived rom a quartz

crystal which is very stable. The Phase locked loop chip outputs a high or low voltage, high or low is

subject to whether the reerence requency input is lagging in phase or leading in phase compared

to the RF input rom the VCO. In other words high i the reerence requency is higher in req than theVCO requency and low i the reerence is lower. The Reerence requency is usually in the range o 1

KHz to 100KHz and also orms the step size o the VCO. A reerence requency o 100KHz can not have

a lower step size than 100Khz. Crystals are physically very large at these requencies so we tend to use

a higher requency crystal and divide it down to our chosen reerence requency. The 100MHz signal

rom our VCO needs to also be divided down to the reerence requency and to do this we need a di-

vide by N counter. N is any number which can divide our requency to the reerence.

The phase locked loop system will comprise o.

1. The VCO (voltage controlled oscillator)

2. The divide by N (100MHz to re. req.)3. A stable crystal or the reerence

4. A xed divider (to divide the crystal to the re. req.)

5. A phase comparator

6. The loop lter (voltage smoother)

In the example below we will use a 8 MHz crystal, a reerence o 100 KHz and the RF requency we will

lock to is 99.9 MHz. The reerence divider is 80 and the RF divider is 999. The 8 MHz crystal is divided

by 80 to 100Khz. This stable signal is ed into one o the inputs o the PLL chip. The RF signal rom the

VCO is ed into the divide by N counter. This counter will need to have N set to 999 to achieve a divide

down rom 99.9 MHz to 100 Khz. When the VCO has a requency o 99.9 MHz both the inputs to the

phase locked loop chip will have the same requency and phase. The output pulses rom the phase

locked loop chip are ed into a loop lter circuit. This low pass lter circuit smoothes and averages the

phase locked loop pulses and produces a dc voltage which is applied to the requency determing ele-

ment o the VCO which is usually a varicap diode. This moves the requency o the VCO and the process

is repeated. This is why the name LOOP is used. The requency is checked against the reerence, the

voltage is changed in respect o any requency error, the voltage is applied to the oscillator, the re-

quency moves. This process is happening continually with the PLL chip adjusting the VCO until it is on

requency and it will keep readjusting to keep it there. I we changed the divide by N number to 997

then the PLL would adjust the VCO until both inputs to the phase comparator were equal in phase and

requency. This would orce the VCO to now have an output o 99.7 Mhz.

The bw broadcast phase locked loop system employs a modern chip that contains an oscillator or aquartz crystal, a divider or the reerence, a divide by N counter and a phase locked loop section (phase

comparator). All o these sections are congurable by serial control. This control is ed rom a bw

broadcast sotware program contained in a microcontroller. The loop lter is built around a standard

op-amp. Some exciters still use many logic chips or the various dividers and associated unctions but

the bw broadcast system uses only two i we do not count the loop lter section.

The problems o Phase Locked Loop systems

The loop lter is the most crucial part o the phase locked loop system and plays the biggest part

in achieving a high quality exciter. The design goal is to have the PLL system get the VCO to the cor-

rect requency ast and to appear transparent. When we FM modulate the VCO we are moving the

requency o the VCO in proportion to the audio signal we apply. The PLL circuits job is to correct anyrequency errors.

Hmmm... Audio introduces requency shits and PLLs try and correct it. You can see that the two do not

DIVIDER MHZ

LOOPFILTER

DIVIDE NPHASE

COMPARE

VCORF OUT

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go hand in hand. I we design the loop lter too well the quick response will strip the audio and not

allow any deviation and hence no or minimum audio. I we relax the requirement to allow better audio

to pass uncorrected then we introduce other problems such as PLL lock time ( the time it takes the

PLL to correct any requency or get the VCO to requency). The ideal PLL system would allow us to get

to requency ast and then somehow relax itsel and change the loop lter characteristics to improve

the audio. We need the PLL circuit to not correct the audio (modulation) as much as when the VCO is

genuinally o requency.Multispeed loop systems.

Multispeed loop systems can be designed in many ways. We have seen and tested systems rom com-

plex to the very complex. We have chosen a system that has a minimum component count and still

retains excellent perormance. We have managed to keep the component part down by putting the

intelligence o the system into sotware. The Dual speed loop system we have used is only 1 extra com-

ponent above our standard single loop system. This component is an analogue switch which has two

o its switches placed across two o the resistors in the loop lter. When out o lock the switch shorts

out the resistors enabling more current to be dumped into the capacitors o the loop lter and hence

quicker charge time and aster lock up. When on channel the switches are opened. The hard part is

knowing when to switch. Some others exciters use the lock detect signals rom the phase comparatorchip to determine when the VCO is in lock. We have ound this to be ar rom perect as high level low

requency content in the audio (heavy bass) can make the lock signal rom the phase comparator read

wrong. This could cause the transmitter to switch to ast lock when heavy bass is applied and then we

would be back to square one, distortion.

Bw broadcast has taken these lock detect signals rom the phase comparator and connected then to

a microcontroller where they are analyzed by a propriority sotware routine to determine whether

the VCO is really ON requency or o requency. The sotware can detect that the VCO is still on re-

quency even i we deviate the carrier with audio by 1 MHz. This enables us to obtain very very low bass

response with very very low distortion gures and still have an accurate lock detect system and ast

lockup time.

Circuit Description

The requency determing element is ormed by coil L1 and varicap diode VD1 together with capacitors

C17 - C20. These components are used as part o a cascode oscillator whose output is then buered

by transistor T3 and T7. The RF output rom T3 and T7 is impedance matched to the base o transistor

T5 by RFT1, a 4 to 1 matching transormer. The high power output rom T5 is impedance matched by

coils L2 and L3 and associated capacitors to the 50 ohm output socket CON2. These components also

provide harmonic ltering.

The PLL circuit is primarily IC2 which is a serially programmable PLL chip. The microcontroller IC3 reads

the dial switches at switch on and outputs a serial code to the PLL chip in a ormat that determines the

output requency that the PLL will try and lock the transmitter to. The PLL chip outputs control pulsesto the loop lter built around op amp IC4. The loop lter takes the sharp pulses rom the PLL chip and

converts them into a smoothed signal ready to apply to the requency determing component, varicap

diode VD1. IC1 is an analogue switch that shorts out two o the resistors in the loop lter which ena-

bles the transmitter to get on requency aster. When the oscillator is on requency the Analog switch

switches out which greatly improves the audio response o the transmitter. The microcontroller IC3

determines when to switch the analog switch in and out by reading the lock detect signals rom the

PLL chip. The microcontroller can also use this inormation to switch o transistor T3 with open collec-

tor congured T4 which mutes the RF output when the transmitter is out o lock. LED1 provides visual

indication o the PLL locked condition.

Audio is ed into the modulation input connector CON1. It is passed through lter FIL1 to remove highrequency energy rom eeding back into the Modulation circuitry. From here the signal passes to vari-

able resistor VR1 where modulation levels can be set. From the output o the variable resistor the audio

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signal passes through resistor R30 and jumper J1. This jumper allows either o capacitors C22 or C23

to be put in parallel with R30 orming a pre-emphasis lter. 0, 50 or 75us is selectable depending on

jumper selection. From here audio is ed via a resistive potential divider to the varicap diode VD1. The

audio imposed onto VD1 causes the requency o the transmitter to shit and modulation is achieved.

There is an expansion connecter on the board to allow connection o other bw broadcast products

such as an LCD requency selector. Connection details are provided with the relevant expansion prod-

uct.

Setup and testingWe recommend that the module be set up with the equipment shown on the ollowing pages. While

the unit is actory tested and should work as expected but we highly recommend that its perormance

be veried with an RF power meter, dummy load, spectrum analyzer, modulation meter and a requen-

cy meter. A radio test set may contain all o these unctions in one box.

Power supply

For correct operation you will need a regulated power supply that is capable o providing 15 volts. The

unit may unction down to13.8 volts but you may lose a little perormance at this lower voltage. Wedo not recommend you exceed 15 volts as this may cause the components to run too hot and possible

damage to the module may occur.

Frequency selection

Beore you turn the power on you must select your requency.

The rst switch represents units o 10 MHz, where 8 would mean 80 MHz. 0 = 10 = 100 MHz

The second switch represents units o 1 MHz where 9 would mean 9 MHz.

The third switch represents units o .1 MHz (100KHz) where 7 would mean 700 KHz

The ourth switch represents units o .0125 MHz (12.5KHz) where 4 would mean 50 KHz

Taking the above as an example i we set switch 1 to 8, switch 2 to 7, switch 3 to 9 and switch our to 0

we would set the PLL to a requency o 87.9 (8X10MHz+9X1MHz+7X.1MHz+0x0.0125MHz)

To reset a new requency you must turn power to the unit o then back on again.

We recommend you ne tune the requency with variable capacitor VC1. Disconnect the audio beore

trying to adjust VC1. You will obviously need the unit on and powered up rst beore this adjustment

can be made.

Audio input and pre-emphasis

Audio is ed in via CON1. I you have a stereo encoder then remove jumper J1. I you have an audio

limiter with pre-emphasis capability then also remove the jumper J1. Otherwise i no stereo encoder or

limiter with pre-emphasis is in line with PLL you should congure jumper J1 to suit the pre emphasis

requirement or your region. 75us or the USA and Japan and 50 or the rest o the world. With youraudio applied at the desired level to the PLL+ adjust variable resistor VR1 or 100 percent modulation (

a maximum peak deviation o +/- 75KHz ) on a modulation meter.

RF output

The RF output can be connected to CON2. The RF output power rom the PLL+ is xed at 1W and can

not be adjusted. Please do not alter the coils L2 and L3 as these are actory set. They orm part o the

harmonic ltering and should not need to be adjusted. I you require less power then we recommend

that you use a resistive attenuator ormed rom three resistors. Details can be ound in any good radio

handbook such as the ARRL handbook. Always connect a 50 ohm load on the output to Avoid damage

to T5.

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IMPORTANT INFORMATION.

This exciter module is a high quality broadband FM exciter that oers OEM manuacturers a low cost

route to FM signal generation without the hassles and expense o designing your own. The RF portion

o this design is currently being used by several manuacturers who have sought and obtained CE and

FCC compliance. When this module is used in conjunction with the notes below you should be able to

do the same.

To unction as BW has intended and to meet the specications quoted we advise OEM manuacturers

to careully review the ollowing important inormation regarding the integration o the module into

your apparatus (piece o equipment.) The inormation will aid you in intergrating this module into your

apparatus and placing the nished piece o equipment on the market. This inormation is especially

important in the modern era with CE/RTTE/FCC regulations on EMC perormance o electronic appara-

tus.

Shielding

Any RF device radiates, the low level RF circuitry on the unit is also susceptible to pick-up o RF elds

and reamplication o them. For these reasons we strongly encourage that the module is encased in a

suitable metal enclosure. This enclosure could be the enclosure or the ull apparatus that the module

is enclosed inside or be a separate enclosure within the external enclosure. We recommend that the

module is placed into a metal enclosure by itsel to prevent possible intererence with any other audio

or r modules in the apparatus main enclosure. The audio and RF ports should employ bulkhead style

connections to the enclosure and any DC power connections should be run through eed-through

capacitors grounded to the enclosure. There are many small RF screening enclosures available com-

mercially that will do the job. These are usually made rom tin plate or tin plated steel and they oer

excellent screening, immunity protection whilst also minimising r emissions. I the module is to be

installed into a single metal enclosure that has any apertures (or ventilation and cooling etc.) then

we recommend that those aperture sizes are suciently small that they stop the emission o RF at the

requencies o interest.

Please see the intergration diagram contained in this manual or more inormation.

We also recommend you consult the reerence books below or more inormation on screening and

aperture sizing.

Power supply

This exciter module is designed to operate as intended when connected to a stabilised 15 volt power

supply that is capable o delivery at least 300mA o continuous current. You must ensure that thepower supply used has an extremely low noise output to prevent modulation o the RF output car-

rier by the noise o the power supply. Using a power supply o inadequate design will degrade the

perormance o this module. We suggest a power supply with RF ltering is used, this will help prevent

the power supply rom suering rom RF intererence which in turn aects the output voltage o the

power supply, adding noise, which will produce noise and possibly side bands on the RF transmission.

I the module is to be installed into its own screening enclosure inside the main metal chassis then we

recommend the power supply to the module is run through eed-through capacitors.

Low pass fltering / RF output

This exciter module has some inherent harmonic as part o its design. This may, or may not be ad-

equate or your application and we suggest you veriy the perormance o the unit with a spectrum

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analyser to ascertain the suitability o this module or your application. This unit is normally used in

conjunction with a power amplier where the harmonic perormance o the exciter module is less

signicant. In the case where you intend direct transmission or low power FM or or cable TV re

broadcasting we suggest you check the regularatory stipulations on harmonic emissions and add an

external low pass lter i required. A spectrum analyser should be used to check harmonic levels. For

compliance.

Exciter audio input, fltering and limiting.

This exciter module has a wide-band input and will require audio bandwidth ltering and or peak lim-

iting in order to prevent over-modulation and to protect adjacent channels.

For stereo multiplex operation this can usually be achieved through the use o a high quality stereo

encoder, which eatures bandwidth limiting and possibly peak limiting as part o its design.

For Mono operation some orm o audio limiting will be required to prevent over-modulation and

protect adjacent channels.

Regardless o stereo or mono operation you should ensure that the audio bandwidth at the input tothe exciter is still within the connes o a stereo multiplex signal (< 60 Khz) to prevent intererence.

A combination o BWs stereo encoders and audio limiters will do the job. A DSP based solution such as

one o the DSPX series o audio processors combines peak limiting and bandwidth limiting and pro-

vides a very high perormance stereo sub-carrier signal suitable or injection into this exciter module.

We recommend a spectrum analyser is employed to measure the output bandwidth o the transmis-

sion. This could also be used to veriy the RF perormance o the exciter and any subsequent ampliers

or lters.

I the exciter modules audio input is to be presented to the outside world (with chassis connections

on the metal enclosure) then we recommend some RFI ltering be employed to aid in emission sup-

pression and to increase immunity to external RF elds rom other equipment or signals in the air.

Some reerences on audio ltering are available below.

Summary

When used in conjunction with BWs recommendations this module will provide a very high class FM

signal. I you would like urther inormation on the integration o RF modules we advise you to contact

BW directly who can provide urther help and advise in the use o this module within your apparatus.

BW can also oer RF testing and EMC emissions and immunity testing or your completed apparatus

through its in house GTEM CELL acility and RF test equipment.

We can also recommend the ollowing books which will provide you with examples and some back-

ground theory on EMC in product design and assembly.

EMC for Product Designers, Third Edition by Tim Williams

Testing for EMC Compliance : Approaches and Techniques by Mark I. Montrose and Edward M. Nakauchi

Introduction to Electromagnetic Compatibility (Wiley Series in Microwave and Optical Engineering) by Clayton R. Paul

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Recommended testing arrangement or mono FM transmitters. For FM ampliers an FM exciter will

need to be placed between the AF signal generator and the power amplier. The power amplier will

substitute the FM transmitter block shown above. For more inormation on test methods please con-

sult ETSI EN 302 018 or other relevant specications or your region.

Recommended testing arrangement or stereophonic FM transmitters. For FM ampliers an FM exciter

will need to be placed between the AF signal generator and the power amplier. The power amplierwill substitute the FM transmitter block shown above. For more inormation on test methods please

consult ETSI EN 302 018 or other relevant specications or your region.

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Recommended testing arrangement to measure cabinet radiation or FM transmitters and FM ampli-

ers. For FM ampliers the input signal shown above will be rom an FM exciter and the power amplier

will substitute the FM transmitter block shown above. For more inormation on test methods please

consult ETSI EN 302 018 or other relevant specications or your region.

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COOLING

FANPOWER AMPLIFIER / FILTERING MODULE

EXCITER

MODULE

RF IN

RF OUT

POWER AMPLIFER / FILTERING PCB

POWER SUPPLY MODULE

MAINS

INLET

FILTER

Feedthrough

capacitors

STEREO ENCODER /

BANDWIDTH LIMITING /

PEAK LIMITING

AUDIO INPUT/S

RF OUTPUT

AUDIO RFI FILTERING

(optional)

SCREENING ENCLOSURE

SCREENING ENCLOSURE

SCREENING ENCLOSURE

MAINS INPUT

GND

G

ND

GN

D

GND

GND

Suggested integration diagram or this module

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Component overlay / position

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Bill O Materials

QTY PART-REFS VALUE

Resistors

3 R1,R27,R32 10R2 R2,R3 1k

4 R4,R21,R28,R29 470R

4 R5,R8,R9,R31 330k

2 R6,R7 10k

2 R10,R11 330R

5 R12,R16,R17,R22,R23 1k2

3 R13,R20,R24 4k7

2 R14,R30 12k

2 R15,R26 220R

1 R18 180R1 R19 68R

1 R25 22R

1 R33 100R

1 R34 33k

Capacitors

3 C1,C36,C39 47pF

4 C2,C3,C6,C35 2.2uF

4 C4,C8,C11,C14 100nF Y5V

2 C5,C7 470uF

5 C9,C25,C28,C32,C38 1nF

4 C10,C15,C21,C29 10nF

3 C12,C13,C16 100uF

3 C17,C24,C37 100pF

1 C18 4p7

2 C19,C30 27pF

1 C20 82pF

1 C22 6n8

1 C23 4n7

2 C26,C40 10uF1 C27 220pF

1 C31 12pF

1 C33 56pF

1 C34 33pF

Diodes

1 D1 DIODE2

Miscellaneous

1 BOX1 RFIBOX1

2 CON1,CON2 MCXPCB4HOLE

1 CON3 2-Way Molex

1 CON4 CONN-DIL10

1 CON5 5WAY MOLEX

1 FIL1 T FILTER

6 H1,H2,X2-X5 PCBHOLE

1 IC1 40661 IC2 MC145170P2

1 IC3 PIC16F627A-I/SO

1 IC4 TL081CD

1 IC5 74HC4067

1 J1 JUMPER3

1 J2 2-Pin Jumper

1 L1 MC120

1 L2 2.5T

2 L3 ,L53.5T

1 L4 0.15uH1 L6 FB

1 LED1 LED

1 REG1 LM78L05ACM

1 RFT1 RFT4TO1

4 SW1-SW4 DECSWITCH

6 T1-T4,T6,T7 PMBTH10

1 T5 2N4427

1 VC1 7-50pF

1 VD1 VARICAP

1 VR1 1k

1 WIRE1 Biliar Wire

1 X1 8MHz

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