Ramsey Electronics FM-100 User guide

Ramsey Electronics Model No. FM-100
Now here’s the ultimate radio transmitter for all of you home
brew DJs out there! This all-in-one stereo transmitter has all
the features you will ever need for transmitting for a school
radio station, around your yard, or even around the block.
With an optional high power module for out of the US
transmitting, this is definitely a professional unit!
•2 Line inputs and one mic input-plus a built in mixer!
•PLL Crystal controlled for rock solid frequency
•Left and right channel peak hold indicators and large LED
frequency display
•Built in power supply, just plug it in!
•25mW output standard, optional 1W module for foreign
country operation
•Auto AGC microphone muting function for cool talk overs
•Rugged steel enclosure for years of use

FM-100 Page 2
PARTIAL LIST OF AVAILABLE KITS
RAMSEY TRANSMITTER KITS
• FM100 Professional FM Stereo Transmitter
• FM25 Synthesized Stereo FM
Transmitter
• MR6 Model Rocket Tracking
Transmitter
• TV6 Television Transmitter
RAMSEY RECEIVER KITS
• FR1 FM Broadcast Receiver
• AR1 Aircraft Band Receiver
• SR2 Shortwave Receiver
• SC1 Shortwave Converter
RAMSEY HOBBY KITS
• SG7 Personal Speed Radar
• SS70A Speech Scrambler
• BS1 “Bullshooter” Digital Voice
Storage Unit
• AVS10 Automatic Sequential Video Switcher
• WCT20 Cable Wizard Cable Tracer
• LC1 Inductance-Capacitance Meter
RAMSEY AMATEUR RADIO KITS
• FX 146 VHF Transceiver
• HR Series HF All Mode Receivers
• QRP Series HF CW Transmitters
• CW700 Micro Memory CW Keyer
• CPO3 Code Practice Oscillator
• QRP Power Amplifiers
RAMSEY MINI-KITS
Many other kits are available for hobby, school, Scouts and just plain FUN.
New kits are always under development. Write or call for our free Ramsey
catalog.
FM-100 PROFESSIONAL STEREO TRANSMITTER INSTRUCTION MANUAL
Ramsey Electronics publication No. MFM-100 Revision 1.1a
First printing: April. 1996 MRW
COPYRIGHT 1996 by Ramsey Electronics, Inc. 793 Canning Parkway, Victor, New York
14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.

FM-100 Page 3
FM-100 PROFESSIONAL
STEREO TRANSMITTER
Ramsey Publication No. MFM-100
Price $10.00
TABLE OF CONTENTS
Introduction ......................................4
How does it work ..............................5
Parts List...........................................13
Assembly Index ................................16
Section Layout ..................................17
Display Layout ..................................18
Main Board Layout............................21,22
Schematic Centerfold .......................34,35
Troubleshooting ................................51
Using the FM-100 .............................57
FCC Rules and Information ..............58
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR

FM-100 Page 4
INTRODUCTION TO THE FM-100
First we will begin with a little history of stereo transmitters at Ramsey
Electronics to give you some idea how we arrived at the FM-100 as our latest
stereo transmitter. We have many people call us each day asking questions
about our earlier versions of transmitters such as the FM-25 and the FM-10a.
Most are questions concerning drifting, sound quality, and transmitting
distance. The tunable FM-10a was a great product for a low-cost entry into the
world of micropower transmitters. The FM-25 was the next step up allowing for
a rock solid stable frequency just like professional stations. The latest step was
to create a transmitter that not only has a rock solid frequency, but also all the
features you would find in a commercial station.
Well, in answer to customer research and comment, here is the result of
months of design and years of stereo transmitter experience. The FM-100 has
all of the features needed to run a professional sounding radio station. It
includes extensive audio filtering to prevent high frequency audio interference,
AGC (Automatic Gain Control) with the microphone to prevent overloading
distortion, a frequency display with easy frequency adjustment, 2 line inputs, 1
microphone input, PLL controlled, CD quality transmission, and more. In other
words we pulled all the stops to bring you a top quality product that will satisfy
even the most discriminating user.
Due to demand from our neighbors down south, and wherever it is legal, we
have allowed for a special module to be added to give you a 1 watt RF output.
Simply plug it right in with a minor adjustment, hook up a good antenna and
bingo, you’re on the air over miles.
We are happy to bring you this truly professional product that will give you
many years of fun, reliable use, and enjoyment knowing that you have built it
yourself.

FM-100 Page 5
HOW DOES IT WORK?
Here is where we get into a little circuit analysis. If you just want to plug it in and
start broadcasting, you can skip this section and read the FCC regulations
section. Otherwise there is some insight into why and how this FM-100 works.
We will use the schematic located at the center of the manual to analyze the
circuit.
We will begin with the power supply since it is the most common circuit we will
see. When you plug a working unit in, 110 VAC is applied across the primary
winding of the transformer T1. This in turn induces 10 VAC across each
secondary winding. The transformer included in your kit is rated for 500mA per
winding, but we have connected two of them in parallel, allowing us to get 1
Amp at 10 VAC. This current is necessary when the high power module is
added into the kit. The module draws a little more than 500mA when
transmitting, which left no more current for the rest of the kit. The displays draw
10mA per segment, and there are a maximum of 29 of them lit at any time. That
is another 290mA, making for a total of 790mA, not including the rest of the
circuitry. As you can see, this project requires a little power to get on the air, so
a substantial power supply is required for good operation.
The output AC of the transformer is fed to a bridge rectifier, where it is
converted to about 12 VDC, and then smoothed out with C86 and C52, both
3300uF capacitors. These big capacitors were required to reduce ripple in the
power supply to a minimum and therefore reducing 120Hz noise in the audio of
the project.
To get a negative supply for the opamps, we make a negative voltage multiplier
which taps some of the AC from the transformer. C89 passes AC, but not DC,
allowing D7 and D6 to rectify the AC through the capacitor to a negative
voltage. C55 then smoothes out the ripple.
Regulators are then used to completely smooth out any remaining ripple and
other noises present on the power supply. The +12 volts is regulated to +5 volts
by VR3, the +5 volts is then used for digital circuitry and some of the audio
circuitry. The +12 volts is also regulated to +8 volts for most of the audio
circuitry, and the major source of power for the high power module. The -12
volts is regulated to -8 volts for just the audio circuitry.
Now we will get on to the display circuit, and why we designed it this way.
Keeping low noise in mind, we wanted a display that produced as little noise as
possible. We determined that an LED display was our best choice for visibility,
but we couldn’t use display drivers that multiplexed. Multiplexing means that all
of the digits are never on at the same time, but each are turned on in turn at a
high enough rate so that to your eye it looks as if all are lit at the same time.
The switching between the displays produced more noise than we wanted to
have to deal with, so we chose a method where all the displays are constantly

FM-100 Page 6
lit. While this may not be the most efficient method of lighting a display, it is the
least noisy. U3, the MM5451 is just a large serial shift register made for driving
LED segments.
Well, the display wouldn’t do much without a smart device to send it some
meaningful data. In this case we are using a Motorola microcontroller (U4) to do
the job for us. This microcontroller performs most of the operations on the unit
such as checking for button presses, setting the transmitting frequency, muting
audio lines at appropriate times, as well as updating the display.
When the frequency is changed, we access U2, a serially programmed PLL
(Phase Locked Loop). When the frequency needs to be set, the information is
sent serially to U2. This information is a string of binary data, (1's and 0's). In
this way data is sent one bit at a time to U2. The frequency information takes
16 bits, and there are an additional 32 bits sent for the internal control of U2.
You may think that all this would take a long time, but in fact the whole process
from the time you press a frequency control switch until the data is completely
sent is less than 1/100th of a second!
The PLL also takes the 6 MHz crystal frequency and divides it by 60 to obtain a
stable reference frequency of 100KHz. How does it know to divide the crystal
frequency by 60? That is part of the data that is sent from U4 each time a
frequency button is pressed. To set the operating frequency of U6, we simply
send U2 divide by N data to produce the desired frequency from the BA1404’s
VHF oscillator. The oscillator’s frequency is divided by this value N, producing
an output in the 100KHz region. The internal phase detector compares the
highly accurate 100KHz reference with the divide-by-N output and controls the
BA1404 oscillator so that the frequencies match precisely.
Using the example from above, a frequency of 95.3 MHz gives an N of 953, so
the frequency from U3 is divided by 953 and then compared with the reference
frequency of 100 KHz. If the desired frequency is less than the reference
frequency U2 increases the output voltage on pin 13. This increases the
voltage across diode D10, a varactor diode. As the voltage across the varactor
increases, it causes a decrease in capacitance (Increasing reverse bias
essentially increases the distance between the capacitor’s plates by increasing
the depletion region in the diode (C = kA/d). The decrease in capacitance
causes an increase in U6’s RF oscillator (fo= 1/[2π(LC)½]), bringing the FM-
100’s output frequency back on frequency. If the desired frequency is higher
than the reference, pin 13 is driven low. If the frequency is just right then pin 13
becomes a high impedance, basically disconnecting it from the circuit so it will
cause no change in the voltage on D10. The voltage changes on pin 13 are
filtered by R8, C9, R7, and C11 to provide a steady, noise free tuning voltage
for D10. In this way the output frequency of U6 is "locked" to that desired by the
microcontroller. Meanwhile U4 is polling pin 11, the LD (Lock Detect) output of
U2 to determine if the PLL can achieve a “lock” or not.

FM-100 Page 7
If you are a close observer, you will notice that U4 derives its clock signal from
the PLL. The PLL has a nifty feature of a buffered divided crystal output to drive
external devices such as microcontrollers. This is another part of the 32 bits we
send to the microcontroller other than the divide by N info. When first powered
on, the XCLK line is at the lowest possible divide by C frequency, which is
6MHz / 16 or 375KHz. This runs the microcontroller at a pretty slow rate until
we can send out new information using a C of 4, giving us a clock of 1.5MHz.
This clock frequency is not only used by the microcontroller U4, but also by U9
and U10, the switched capacitive filter circuitry that we will talk more about in a
minute.
U1 is a serially accessed EEPROM, which stores our frequency settings for the
next time we power up the FM-100. This prevents us from having to go through
setting the proper frequency every time we turn off the FM-100. The frequency
data is only set to the EEPROM when the user exits the setup mode, and a
confirming beep from SP1 lets the user know it is written.
U6, the BA1404 FM stereo transmitter IC is what does all the work of creating
your stereo subcarrier, and doctoring your audio signals for transmission. The
BA1404 was originally designed to run from a couple of 1.5 volt batteries, so it
was made to be run at a low voltage. We decided to use a 2.5 volt regulator
(VR1) to give us the proper voltage at the greatest noise immunity from the
power supply. The low level RF output of U6 is then fed to Q2 and surrounding
parts to boost it to a more reasonable level for filtering. Since the RF output of
the BA1404 is not the cleanest, much filtering is required to remove unwanted
transmissions that are outside of the FM band.
The primary filter for the job is the bandpass filter consisting of C84, L5, L4,
C82, L6, and C85. This has a lower cutoff at about 70MHz, and an upper cutoff
at 120MHz. The output of this filter is sent to a class C amplifier consisting of
Q1 and R32. This gives us a higher level output which is adequate for local
broadcast. But before going to the antenna, we low pass filter the output at
110MHz. This gets rid of the unwanted upper harmonics that are very present
in a class C amplifier. Harmonics are multiples of the primary frequency and the
primary one we are trying to get rid of is the second harmonic (F x 2), which in
our case winds up in the aircraft band. It is extremely important for us not to
interfere with ANY other transmissions in ANY band. These filters will keep us
from doing any harm outside our intended transmission band.
Now that we’re done talking RF, we can get on with the audio. We will begin
with the microphone amplifier. U7, a voice detector chip is used in this circuit. It
has a couple features that we use in the FM-100 that really help us out. One
feature is the AGC or Automatic Gain Control. This prevents us from
overloading the audio circuitry by getting excited and yelling in the microphone.
When the amplitude of the signal coming from the microphone increases, the
gain of the microphone amp decreases, keeping its output relatively the same
over varying input levels.

FM-100 Page 8
The second neat feature is the voice detection capability. Voice detection is
used with the auto AGC feature of the FM-100. Essentially pin 8 of U7 goes
high when there is a varying signal level seen on the microphone, as compared
to the constant level of background noise. When pin 8 goes high, it turns
JFETS Q5 and Q6 on which act like voltage controlled pots. The more they are
turned on, the less resistance is seen from source to drain. This in turn mutes
the audio from the line level inputs, allowing only the microphone to be heard
when there is voice detection active.
U4, the microcontroller, has the ability to override this feature by setting the
connection marked AUTOAGC high, thereby turning Q7 on, which disallows Q5
and Q6 from turning on. The microcontroller can also mute the microphone
audio by setting the MUTE line high, thereby turning Q4 on, grounding out all
the microphone audio. R21 and C37 smooth out the switching transitions so
that there is very little popping heard that is apparent in most switches. This
MUTE line is also used to turn on the microphone line when the speaker
sounds a tone on the unit. This prevents the tone from being transmitted over
the air.
In our description of the audio we will only be talking about the right channel
circuitry in the FM-100, since the left channel is identical. Line level audio is
applied to J5 or J6, and then on to R62 or R84. R62 and R84 control each line
level’s transmission volume. These levels are then summed in U8:A, so now
both signals are present on pin 1 of U8. This signal is then sent through R63,
which when combined with Q5 gives the voice detector circuitry the ability to
mute the audio. The audio continues to U8:B, where it is summed with the
microphone audio. The microphone audio level is controlled by R26, and is sent
to both the left and the right channels. The microphone audio combined with
the line level audio passes then on to U9, a switched capacitor filter.
U9 is an 8th order Butterworth switched capacitor low pass filter. It doesn’t
require reactive components like capacitors, inductors and resistors to set its
operating frequency, instead its frequency is set by a clock reference. In this
case it is 1.5MHz from the PLL that we discussed earlier. The actual operating
frequency is then 1.5MHz divided by 100, or 15KHz. Anything over this
frequency, like high frequency tones from cheap CD players and people with
squeaky voices, is simply cut out to prevent interference with the stereo
subcarrier in the BA1404.
U9 also has a built in op-amp which we use for our 75uS equalization. This
equalization conforms with the standards for North America FM broadcast. The
audio is then sent to U11:A for further low pass filtering. This filter gets rid of the
1.5MHz clock signal that may be present in the audio from the MAX291 (U9).
Now we have nice clean audio all doctored up for serving across the airwaves.
The audio is then sent to R23, which sets the relative audio level to be
transmitted.

FM-100 Page 9
Part of the output of U11:A is observed for the level indicators. IC U11:B, D4,
R54 and C60 comprise a peak hold detector. Part U11:B and D4 make up a
real diode, meaning there is no .7 volt drop normally associated with a diode
because it is accounted for in the feedback of the opamp. The “real diode” will
charge C60 quickly on positive going signals, but it doesn’t discharge it. The
discharge cycle is left up to R54. The larger the value, the longer in time the
peak hold function is. The voltage on the peak hold is then observed by using a
LM3915 bargraph display driver U12 and a ten segment bargraph. This part is
pretty self explanatory, it’s really just a voltage meter with a log scale instead of
a linear one.
The whole process of filtering, mixing and level detecting is repeated in the left
channel as well. This completes the basic analog circuit description of the FM-
100, but you may be interested in more detail of how it works. If so, there are
many good books and magazines which deal with circuitry of this sort in smaller
manageable circuits which can help you delve further in what is going on.

FM-100 Page 10
MICROCONTOLLER DESCRIPTION
The coding of the microcontroller is set up for a simple process of changing
frequency. As you will see, there is more than meets the eye, but it’s not so
complex when you give it a look.
We will start with two given conditions: 1) The unit is powered up, and 2) The
unit has been set in setup mode. In this state the tens decimal point is blinking
and your frequency may be changed.
1. User presses FREQ UP button.
2. Microcontroller stops scanning the LD (Lock Detect) line, sees what key the
user has pressed.
3. It’s a Frequency key, is the unit in setup mode?
4. Yes, increase the frequency value in RAM by 200KHz.
5. Send the appropriate divide by N to the PLL (U2) along with the rest of the
required data.
6. Decode the display digits, then send the correct bits to the display.
7. Mute the microphone.
8. Send confirm beep.
9. Un-mute the microphone.
10. Wait for key release, if no key release after some time, repeat from step 4.
11. Continue polling LD and updating status indicators.
We hope all of this information helps you understand better what is going on in
the FM-100, and will lead to some insight when you are having assembly
troubles or something isn’t working properly. Remember most projects like this
are made up of many smaller ones, all you have to do is break them down to
understand them better. Now on to building!!!

FM-100 Page 11
RAMSEY “LEARN-AS-YOU-BUILD” ASSEMBLY STRATEGY
Be sure to read through all of the steps, and check the boxes as you go to be
sure you didn't miss any important steps. Although you may be in a hurry to see
results, before you switch on the power check all wiring and capacitors for
proper orientation. Also check the board for any possible solder shorts, and/or
cold solder joints. All of these mistakes could have detrimental effects on your
kit - not to mention your ego!
Kit building tips:
Use a good soldering technique - let your soldering iron tip gently heat the
traces to which you are soldering, heating both wires and pads simultaneously.
Apply the solder on the iron and the pad when the pad is hot enough to melt the
solder. The finished joint should look like a drop of water on paper, somewhat
soaked in.
Mount all electrical parts on the top side of the board provided. The top side is
clearly marked with the word “TOP”, you can’t miss it. This is the side that has
little or no traces on it, but is covered with mostly copper. When parts are
installed, the part is placed flat to the board, and the leads are bent on the
backside of the board to prevent the part from falling out before soldering (1).
The part is then soldered securely to the board (2-4), and the remaining lead
length is then clipped off (5). Notice how the solder joint looks on close up,
clean and smooth with no holes or sharp points (6).

FM-100 Page 12
Since this is a “professional” transmitter, we sincerely hope you put this to-
gether in a professional manner. This project will not work as well as you
wished if you just slap it together without following good assembly techniques,
and follow all instructions. No matter how clear we may think our manual is, if
you have any questions give us a call at the factory instead of jumping to con-
clusions, we will be happy to help you with any problems.
This is a mixed signal project meaning there is digital, audio, and RF circuitry all
in one unit. As with all RF circuitry, we want to mount the parts AS LOW AS
POSSIBLE to the board. A 1/4” lead length on a resistor not mounted close to
the board can act as an inductor or an antenna, causing all sorts of problems in
your circuit. Be aware though that there are stand up components in your cir-
cuit. They don’t need to be squished to the board, but keep the portion of the
resistor closest to the board mounted right on the board.
For each part, our word "Install" always means these steps:
1. Pick the correct part value to start with.
2. Insert it into the correct PC board location, making sure the part is
mounted flush to the PC board unless otherwise noted.
3. Orient it correctly, follow the PC board drawing and the written directions
for all parts - especially when there's a right way and a wrong way to solder
it in. (Diode bands, electrolytic capacitor polarity, transistor shapes, dotted
or notched ends of IC's, and so forth.)
4. Solder all connections unless directed otherwise. Use enough heat and
solder flow for clean, shiny, completed connections.
Keeping this in mind, lets begin by sorting out our components and cross-
checking them against the parts list to make sure we have received everything.
NOTE TO NEWCOMERS: If you are a first time kit builder you may find this
manual easier to understand than you may have expected. Each part in the kit
is checked off as you go, while a detailed description of each part is given. If
you follow each step in the manual in order, and practice good soldering and kit
building skills, the kit is next to fail-safe. If a problem does occur, the manual
will lead you through step by step in the troubleshooting guide until you find the
problem and are able to correct it.

FM-100 Page 13
RAMSEY FM-100 PARTS LIST
Semiconductors
1 MC145170 Serially programmed PLL (U2)
1 BA1404 Stereo generator IC (U6)
2 LF347 Quad low noise opamps (U11,8)
1 68HC705J2 Custom programmed microcontroller (U4) Marked FM-100
1 X2402 serial EEPROM (U1)
2 LM3915 Log bar-dot bargraph display drivers (U12,U5)
2 MAX291 8th order Butterworth lowpass switched capacitive filters
(U9,10)
1 MC2830 Voice activated switch with AGC (U7)
1 MM5451 Serial shift register display driver (U3)
1 79L08 -8 volt voltage regulator (TO92 package) (VR4)
1 7808 +8 volt voltage regulator (TO-220 package) (VR2)
1 7805 +5 volt voltage regulator (TO-220 package) (VR3)
1 78L02 +2.5 volt voltage regulator (TO-92 package) (VR1)
2 10 segment bargraph displays (D11,12)
2 Small red LEDs (D2, 3)
2 Dual Common Anode LED displays (DS1, 2)
6 1N4002 rectifier diodes (Black with white stripe on one end)
(D6,7,21,22,23,24)
5 1N4148 small signal switching diodes (small orange glass body with
black stripe) (D1,4,5,8,9)
1 BB609 Varactor diode (black diode with green band) (D10)
3 BS170 N-Channel enhancement TMOS FETs (Q4,5,6)
2 2SC2498 or 2570 NPN UHF Bipolar transistors (Q1,2)
2 2N3904 NPN General purpose transistors (Q3,7)
Resistors
1 10 ohm resistor (brown-black-black) (R9)
1 51 ohm resistor (green-brown-black) (R73)
1 100 ohm resistor (brown-black-brown) (R16)
3 270 ohm resistors (red-violet-brown) (R30,32,36)
2 330 ohm resistors (orange-orange-brown) (R1,4)
1 470 ohm resistor (yellow-violet-brown) (R11)
18 1K ohm resistors (brown-black-red) (R18,19,20,29,33,39,44,47,
50,53,59,64,71,76,82,86,87,89)
3 4.7K ohm resistors (yellow-violet-red) (R42,61,69)
1 8.2K ohm resistor (gray-red-red) (R13)
23 10K ohm resistors (brown-black-orange) (R2,5,6,8,10,12,14,17,40,
41,49,55,56,57,60,63,68,70,78,80,83,85,88)
4 15K ohm resistors (brown-green-orange) (R22,27,58,66)
2 22K ohm resistors (red-red-orange) (R31,65)
1 33K ohm resistors (orange-orange-orange) (R24)

FM-100 Page 14
7 47K ohm resistors (yellow-violet-orange) (R21,28,34,54,67,72,79)
4 75K ohm resistors (violet-green-orange) (R45,52,77,81)
4 100K ohm resistor (brown-black-yellow) (R7,51,75,91)
1 150K ohm resistor (brown-green-yellow) (R46)
1 220K ohm resistor (red-red-yellow) (R25)
3 1M ohm resistors (brown-black-green) (R3,38,48)
Ceramic capacitors
1 5pF ceramic capacitor (marked 5 or 5K) (C15)
4 10pF ceramic capacitors (marked 10 or 10K) (C18,27,32,82)
2 27pF ceramic capacitors (marked 27 or 27K) (C1,2)
4 47pF ceramic capacitors (marked 47 or 47K) (C29,31,84,85)
1 75pF ceramic capacitor (marked 75 or 75K) (C30)
6 100pF ceramic capacitors (marked 100 or 101) (C13,40,46,64,70,91)
1 220pF ceramic capacitor (marked 220 or 221) (C34)
15 .001uF ceramic capacitors (marked .001 or 102) (C7,8,14,24,25,26,
28,36,41,45,62,75,87,88,90)
2 .0047uF ceramic capacitors (marked .0047 or 472) (C61,74)
13 .01uF ceramic capacitors (marked .01, 10n, or 103) (C3,10,17,20,
21,48,49,53,54,79,80,81,83)
6 .1uF ceramic capacitors (marked .1 or 104) (C4,9,22,51,66,68)
Electrolytic capacitors
1 1uF electrolytic capacitor (C38)
1 2.2uF electrolytic capacitor (C12)
25 10uF electrolytic capacitors (C6,11,16,19,23,33,35,37,39,42,43,44,56,
58,60,63,65,67,69,71,72,73,76,77,78)
2 47uF electrolytic capacitors (C47,59)
2 100uF electrolytic capacitors (C5,50)
2 1000uF electrolytic capacitors (C55,89)
2 3300uF electrolytic capacitors (C52,86)
Variable Resistors
2 1K ohm trimmers (orange top marked 102) (R23,35)
1 10K ohm board mount pot (R26)
2 10K ohm dual pots (R62,84)
1 100K ohm trimmer (orange top marked 104) (R15)
Inductors
1 adjustable shielded metal can coil or similar (L1)
4 40nH coils (small 4 turn air coils) (L2,3,5,6)
1 Small red torroid core (L4)
8” #26 enamel wire for winding (L4)

FM-100 Page 15
Miscellaneous
1 38KHz crystal (Y2)
1 Mini speaker (SP1)
2 Stereo RCA jacks (J5,6)
1 6 pin Molex connector (J10)
1 4 pin Molex header (J11)
4 5 pin headers (J1,3,7,8)
5 DPDT Push button switches (S1,2,3,4,5)
1 20 pin IC socket
1 3.5mm phono jack (J4)
1 Whip antenna (ANT1)
1 18 pin IC socket
1 PC-20-500 Power transformer (T1)
1 Transformer mounting bracket
1 Heatsink (HS1)
1 6 MHz crystal (Y1)
Case and knob parts
5 Push button switch caps
3 Set screw knobs
1 Bottom case half with pre-attached membrane panel
1 Top case half
14 4-40x1/4 board mounting screws
6 6-32x1/4 self tapping black case screws
2 4-40x5/8 self tapping machine screws
1 Fuse holder with hardware
1 1 Amp fuse
1 110 Volt line cord with plug and pre-installed Molex pins
1 Line cord grommet
1 Antenna grommet
4 Rubber leg pads
1 Chassis mount F connector and mounting nut
1 4” piece of hookup wire
7 4-40 Kepnuts
Other Equipment (Not included)
1 Pencil type soldering iron (30-40 Watts) Don’t use a solder gun!
1 Roll of fine 60/40 solder (less than .045” diameter)
1 Sensitive voltmeter or DMM
1 An FM radio for testing
1 Audio sources such as a tape deck, CD player, or microphone
1 Egg carton or grapefruit holder to sort out parts in.

FM-100 Page 16
PROJECT ASSEMBLY
Here we go! To make assembly easier and to stick by the “Learn As You Build”
strategy, we will section off the project into different major circuit groups. We
will begin with the smaller display board to perfect your assembly skills before
we continue with the more crowded sections of the board. Following is a list of
all the sections in the manual that we will be going into:
[A] Display Board.................................... 18
[B] Part Preparation................................ 23
[C] Microphone Amp............................... 24
[D] Mixers................................................. 25
[E] Switched Capacitive Filters ............. 27
[F] Peak Hold and Active Filters............ 29
[G] Transmitter ........................................ 31
[H] Microcontroller.................................. 37
[I] EEPROM Circuit ................................ 38
[J] Jacks and Switches .......................... 39
[K] Power Supply .................................... 41
[L] 1 Watt Module.................................... 44
[M] Rear panel wiring.............................. 45
[N] Front Panel Assembly ...................... 47
[O] PCB Mounting ................................... 47
[P] Final Testing and Calibration........... 48
[Q] Final Case-up .................................... 50

FM-100 Page 17
SECTION LAYOUT ON MAIN BOARD

FM-100 Page 18
DISPLAY BOARD LAYOUT
Parts Layout
Parts Values
Note: Gray
components are on
the reverse side of
the board.

FM-100 Page 19
A. DISPLAY BOARD
We will begin with the display board oriented in the direction shown. Be sure
not to confuse the sides of the board where the parts go. On the board you will
see the side marked FRONT, which is where most parts are mounted. We will
begin with lower parts and work up to the higher ones. Don’t use sockets for
these parts since they need to fit between the front panel and the PC board.
1A. Install R87, a 1K ohm resistor (brown-black-red).
2A. Install R59, another 1K ohm resistor (brown-black-red).
3A. Install R13, a 8.2K ohm resistor (gray-red-red). This resistor sets the
current to each of the display segments and LEDs driven from U3.
Lowering the value of this resistor increases the brightness of the display,
but then the display will draw more current. This resistor was selected for
best brightness/current trade-off.
4A. Install U12, one of the LM3915 Log scale bargraph driver ICs. Make
absolutely sure before soldering that you have installed all 18 pins into the
appropriate holes. Also check the notch or dot indicating pin one is facing
in the same direction as shown in the parts layout diagram. Solder all 18
pins, checking for solder bridges when done.
5A. Install U5, the other LM3915 Log scale bargraph driver. Again make
sure all 18 pins are through the board and that the IC is in the correct
orientation.
6A. Install U3, the MM5451 40 pin IC. Again make sure the notch is in the
same direction as shown in the parts layout, and that all 40 pins are
through the board before soldering. This IC drives all the individual
segments of the display without multiplexing it.
7A. Install D12, one of the ten segment bargraph displays. You will notice
a small divot or notch on one corner of the bargraph indicating where pin 1
is. This will be installed in the same orientation as the notch in the parts
layout diagram. Solder all 20 pins.
8A. Install D11, the other 10 segment bargraph display. Make sure to align
this in the same way as before and solder all 20 pins.
9A. Install DS2, one of the two digit displays. Notice how there isn’t any
indication of pin 1 on these. In this case we want to orient the lettering on
the one side towards U3, so that when looking at the display, the lettering
is facing downward. Solder all 18 pins.
10A. Install DS1, the other two digit display. Again orient the lettering

FM-100 Page 20
towards U3 before soldering all 18 pins.
11A. Install D2, one of the small red LEDs. You will notice that if you look
straight at the LED there is a flat side. This indicates the Cathode side of
the LED. The Cathode side is also indicated by the shorter of the two leads.
Make sure to install the flat side or the shorter lead in the same way as
shown in your diagram. They only light up if they are installed correctly.
Before soldering though, this and the next LED are the only parts that we
do not mound flush to the PC board. In this case we want to mount them so
the lens of the LED is at the same height as DS1 and DS2. These LEDs will
eventually be lining up with holes in the front panel. Once the height is set,
bend the leads to hold the LED in place, then solder.
12A. Install D3 in the same fashion, making sure it is at the same height
and orientation as in the previous step.
Now would be a good time to check all of your solder connections for opens
and solder bridges on the back side of the board. Now we are moving on to
install jumper connections and a capacitor on the back side of the board. The
parts on the back side of the board are marked in gray instead of black.
13A. Install J3, a five pin jumper block, short leads go into the board. Again
make sure you are putting them in the opposite side of the board from
where the rest of the parts are located. This jack is where the numeric
display gets its power and the data for display values.
14A. Install J7, another five pin jumper block. This is where the power for
the bargraphs is applied and the signal levels for the bargraphs are sent.
15A. Install C78, a 10uF electrolytic capacitor. Notice this is the first
capacitor of this type. You want to be sure that you pay close attention to
the polarity markings on this part. In most cases the negative (-) side is
marked on the capacitor, while the positive side (+) is marked on the parts
layout. If you fail to mount this component correctly, the part can fail as well
as prevent proper operation of your project. We will be installing many more
of these later in the project so be sure and remember this!
Cool! We have just completed the display board and we are almost ready to
move on. First we want to check our display board to make sure there are no
solder bridges or cold solder joints. Next check orientation of your parts for
correct installation.
A
K
1/4"
Same height
as DS1+DS2