Ramsey Electronics FM10C User manual

FM10C 1
FM STEREO
TRANSMITTER
Ramsey Electronics Model No. FM10C
 Great for transmitting your tape deck or CD player throughout the
house, yard or even your car.
 Powerful enough for college or neighborhood radio stations - in
use all over the world.
 Fantastic audio quality sounds better than most stations on the
dial. And we’ll tell you why!
 Easily connects to the line-level outputs on any tape deck, stereo
system or CD player.
 Some users hook up one channel to the scanner and the other to
their two way radio. Now you can hear what’s going on around
town up to several blocks away from your house with a simple
stereo receiver... and adjust the volume of each individually with
your balance control!
 Add a mike-mixer and tape/CD deck for a “PRO” sounding station.
 Operates on 5 to 20 volts, using a crystal controlled subcarrier.
 Tunable anywhere in the 88-108 MHz FM band.
Own and operate your own FM Stereo broadcast station.
Definitely not a toy, the FM-10C has an exceptional transmission
range... and the audio quality puts your favorite radio station to
shame. See why this is one of our most popular kits!

FM10A 2
PARTIAL LIST OF AVAILABLE KITS
RAMSEY TRANSMITTER KITS
FM25B FM Stereo Transmitter
AM1, AM25 AM Transmitters
TV6 Television Transmitter
FM100B Professional FM Stereo
Transmitter
RAMSEY RECEIVER KITS
FR1 FM Broadcast Receiver
AR1 Aircraft Band Receiver
SR2 Shortwave Receiver
AA7 Active Antenna
SC1 Shortwave Converter
RAMSEY HOBBY KITS
SG7 Personal Speed Radar
SS70A Speech Scrambler
MX5, MX-10 Mixers
MD3 Microwave Motion Detector
PH14, 15, 16 Peak hold Meter Kits
TFM3 Tri-Field Meter Kit
STC1 Stereo Transmitter Companion
RAMSEY AMATEUR RADIO KITS
DDF1 Doppler Direction Finder
HR Series HF All Mode Receivers
QRP Series HF CW Transmitters
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 STEREO TRANSMITTER KIT INSTRUCTION MANUAL
Ramsey Electronics publication No. MFM10C Revision 2.1b
This Printing: July 2010
COPYRIGHT 2007-2010 by Ramsey Electronics, LLC, 590 Fishers Station Drive, Victor, New
York 14564. All rights reserved. No portion of this publication may be copied or duplicated
without the written permission of Ramsey Electronics, LLC. Printed in the United States of
America.

FM10C 3
FM10C FM STEREO
TRANSMITTER
Ramsey Publication No. MFM10C
Manual Price Only: $5.00
TABLE OF CONTENTS
Introduction to the FM10C ........................................4
FM10C Circuit Description........................................5
Parts Layout Diagram ...............................................7
Parts List...................................................................8
Assembly Instructions...............................................11
Choosing an Operating Frequency...........................16
Schematic Diagram ..................................................18
Adjusting your FM10C..............................................20
Using FM10C Within the Home ................................21
Power Supply Considerations...................................21
LED Power On Indicator...........................................21
Experimental Broadcasting Projects.........................22
Antenna Ideas...........................................................23
Troubleshooting Guide .............................................24
Appendix A: FCC Rules and Information..................25
Appendix B: Understanding Field-Strength ..............28
Summary ..................................................................30
FM10C Kit Warranty 35
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR
RAMSEY ELECTRONICS, LLC
590 Fishers Station Drive
Victor, New York 14564
Phone [phone]
Fax [phone]
www.ramseykits.com

FM10A 4
INTRODUCTION
The Ramsey FM10C is a true STEREO FM broadcast transmitter, which any
person may build and use in accordance with the rules of your nation’s
telecommunications authority. For U.S. residents, that authority is the
Federal Communications Commission (FCC). The FM10C's low-power
broadcasting capability and other practical uses can be fun and interesting
for people of all ages, but the FM10C is definitely not a toy. We will refer to
the FCC regulations frequently in this manual and provide you with some
information necessary to enjoy the FM10C's capabilities in accordance with
the law.
Typical uses for the FM10C include the following:
 Extension of home stereo system - without wires.
 Listening aid for auditoriums, churches.
 Student-operated school radio station.
 College dorm favorite music broadcast service.
 Short-range, two-channel experiments and demonstrations.
We think you will be very pleased with the transmitting range, audio quality,
frequency stability and stereo channel separation of this build-it-yourself FM
stereo transmitter. If you follow our assembly directions carefully and use
your FM10C in accordance with applicable FCC rules, a whole new world of
sharing music, news and views with friends and neighbors awaits you.
Since the sharing of music and information is vital to the culture of our late-
20th-century global community, we realized that our FM10C low-power FM
Stereo Transmitter kit was certain to attract worldwide interest among
hobbyists, students and "pioneers." While the use of the FM10C may need
to be limited to "wireless stereo extensions" in some USA households (to
comply with FCC Rules, Part 15), we have seen it serve very well as a
serious, though simple, broadcast station for remote villages throughout the
world where low cost AM-FM receivers are available to people of all
economic levels. After you're done building your kit, sitting back and
listening to your handiwork, consider this: many other FM10C’s just like
yours are faithfully relaying news and information to listeners in remote parts
around the world. The FM10C is most definitely not a toy!

FM10C 5
CIRCUIT DESCRIPTION
Power Supply
The FM10C can be powered with a standard 9 Volt battery or an external DC
supply. When a standard external female 2.1MM power plug is inserted into
J3 its SW contact is removed from its RING contact. This disconnects the
battery from the FM10C’s circuit. S1 applies power to the circuit. L3 and
C3 are a low pass filter designed to prevent RF (Radio Frequencies) from
entering the unit through the power cord. C4 is a filter capacitor that reduces
60 or 120Hz ripple from an external supply. VR1 is a voltage regulator de-
signed to provide 2.6 Volts DC output with a 5 to 20 Volt DC input. Regula-
tors will also provide low frequency filtering. C9 is a low frequency output
filter. C15, C16, C17, C21, and C25 are high frequency filter caps that are
placed physically as close to the supplied devices as possible.
U1 FM Stereo Transmitter IC
FM stereo transmitter IC (U1) is at the heart of the FM10C. It contains a ste-
reo modulator that develops a main L+R signal, a sub (L-R) signal, a 19kHz
pilot signal, and RF Carrier (88-108 MHz). The control of U1 is determined
by its surrounding circuitry as described in the following paragraphs.
Audio
We will look only at the left channel circuitry since the right channel is
identical to the left. J1 is an RCA connector that brings the left channel au-
dio into the FM10C. L2 and C2 form a low-pass filter that reduce any RF
brought in by the audio cables. R2 is a dropping resistor used to decrease
the audio level into R4. R4 allows the user to set the level of audio that
reaches U1. C6 and R6 set the pre-emphasis characteristics for the region
you intend to operate (75 µs for USA, 50 µs for Europe). C8 is a coupling
capacitor that allows the audio to pass but prevents DC bias from the IC from
being affected by the setting of R4.
Multiplexer Balance
R7 sets the multiplexer balance of U1. This control should be set to mid-
range.
Stereo Generator
C11, C12, X1, and U1 form a 38 kHz oscillator that is used by U1 to create
the 19 kHz pilot frequency for stereo generation.
Multiplexed Audio/Pilot
U1 pin 13 is the pilot output. U1 pin14 is the multiplexed audio output. R8
sets the pilot signal level and R9 sets the multiplexed audio level going back
into U1 at pin12.

FM10A 6
RF Oscillator
This oscillator consists of U1, C19, C20, L4, and C18. The setting of L4 and
the value of C18 sets the RF Carrier frequency that is received by a standard
FM radio.
RF Amp
C22 is a coupling capacitor that allows the RF output at U1 pin 7 to be passed
to the transistor Q1. R11 sets the bias or operating point of Q1. R12 is the
collector load resistor that develops the output signal and brings in DC power.
RF Output
C23 couples the RF output signal to the on-board whip antenna if used (not
used if external output jack is used.
C24 couples the RF signal to the RF output jack J4. L5 clamps the DC level
from the antenna to the ground plane of the circuit board. R13 helps prevent
static discharges from damaging the RF amp.

FM10C 7
FM10C PARTS LAYOUT DIAGRAM

FM10A 8
PARTS LIST
CAPACITORS
1 1 pf disc capacitor [marked 1] (C26)
4 10 pf disc capacitor [marked 10 or 10K] (C11,12,19,20)
1 15 pf disc capacitor [marked 15] (C18, see note #1 at end of list)
1 22 pf disc capacitor [marked 22] (C18, see note #1 at end of list)
1 27 pf disc capacitor [marked 27] (C18, see note #1 at end of list)
3 100 pf disc capacitor [marked 100 or 101] (C1,C2,C3)
1 220 pf disc capacitor [marked 220 or 221] (C13)
8 .001 µF disc capacitor [marked .001 or 102 or 1 nf)
(C15,16,17,21,22,23,24,25,)
2 .0047F disc capacitors [marked 472] (C5,6)
4 10 F electrolytic capacitors [C7,8,10,14)
1 100 F electrolytic capacitor (C9)
1 1000 F electrolytic capacitor (C4)
INDUCTORS
3 2.2 uH [red-red-gold] (L1,2,3)
1 13 turn air core inductor (L5)
1 Adjustable shielded inductor coil (L4) [small square silver “can”)
RESISTORS
1 200 ohm 1/2 watt [red-black-brown) (R12)
1 270 ohm [red-violet-brown] (R10)
1 1K ohm [brown-black-red] (R13)
1 4.7K ohm [yellow-violet-red] (R9)
3 10K ohm [brown-black-orange] (R11,5,6) (R5,6 see note #3 at end of
list)
2 13K ohm [brown-orange-orange] (R1,2)
2 15K ohm [brown-green-orange] (R5,6) (R5,6 see note #3at end of
list)
1 180K ohm [brown-gray-yellow] (R8) (see note #2)
1 220K ohm [red-red-yellow] (R8) (see note #2)
1 470K ohm [yellow-violet-yellow] (R8) (see note #2)
2 1K yellow trimmer potentiometer [marked 102] (R3,R4)
1 100K yellow trimmer potentiometer [marked 104] (R7)
SEMICONDUCTORS
1 78L02 +2V regulator(VR1)
1 2SC2570A NPN VHF transistor (Q1)
1 BA1404 Stereo modulator IC (U1)

FM10C 9
Jacks
2 RCA-type PC-mount jacks (J1,2)
1 2.1 MM power jack (J3)
1 F-type PC-mount jack (J4)
HARDWARE AND MISCELLANEOUS
1 Ramsey FM10C Printed circuit board
1 38 KHz crystal [small silver cylindrical "can" with 2 small leads], taped
to a piece of paper.
1 PC board mounted DPDT switch
1 18 pin IC socket for BA1404
1 9-volt battery hold-down clamp
1 9-volt battery snap connector
1 Whip antenna w/screw
1 Plastic alignment screwdriver
1 Case with top, bottom, front, and back panels
4 4-40 x 3/13 (Short) Philips head screws
2 4-40 x 1-1/4 (Long) Philips head screws
4 Rubber feet
1 Button for DPDT switch
REQUIRED, NOT SUPPLIED:
9-volt alkaline or heavy-duty battery
Shielded stereo audio cables
Line-level output audio source (such as a tape deck or CD player)
OPTIONAL
LED "power on" indicator and 1K resistor
Audio switching-mixing accessories of your choice
External antenna, small gauge coaxial cable with F-connector (example
RG-6).
NOTES:
1. Selecting 18, 22, or 27 pf for C18; establishes the FM-band fre-
quency adjustment range. See “Choosing an Operating Fre-
quency.”
2. Selecting 180K, 220K, or 470K pf for R8; establishes the stereo pilot
level for the desired FM-band frequency to be used. See “Choosing
an Operating Frequency.”
3. R5 and R6 set the pre-emphasis of the transmitter. For 75 uS (USA)
use 15K ohm resistors. For 50uS (Europe) use 10K ohm resistors.

FM10A 10
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 to 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 topside of the PC board. This is the side that
has few or no traces on it, the side with the silkscreen writing. 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 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 close up, clean
and smooth with no holes or sharp points (6).

FM10C 11
ASSEMBLING THE FM10C
Sort out all of your parts to begin with, making sure you have all of the parts
required. You can use old egg cartons to hold various parts to make them
easier to find. Make sure to mount parts on the correct side! You will want to
use the parts layout diagram to assist you in finding where the parts go.
Warning: Use only rosin core solder or solder designed to be used with elec-
tronic equipment. Use of acid core solder will void your warranty and produce
a board that will disintegrate in a short period of time.
Note: Save the excess leads cut from installation of resistors and electrolytic
capacitors to use for straps for the crystal and the battery clip.
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. We will be happy to help
you with any problems you may run into.
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. Keep the portion of the re-
sistor 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. Make 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.

FM10A 12
1. Orient the board in the same direction as the parts layout diagram.
2. Install the 18 pin IC socket. If the socket has a notch in one end,
install it in the same position as shown on the Parts Layout Diagram to
prevent confusion later.
Audio Section
3. Install L2, a 2.2uH inductor (red-red-gold). Inductors have no polar-
ity so they may be installed in either direction.
4. Install L1, another 2.2uH inductor (red-red-gold).
5. Install C1, a 100pF ceramic capacitor (Marked 101). Ceramic ca-
pacitors are just like inductors they have no polarity so they may be in-
stalled in either direction.
6. Install C2, another 100pF ceramic capacitor (marked 101).
7. Install R1, a 13K ohm resistor (brown-orange-orange). Resistors are
similar to inductors they have no polarity so they may be installed in ei-
ther direction.
8. Install R2, another 13K ohm resistor (brown-orange-orange).
9. Install R3, a 1K ohm trimmer potentiometer. The top is orange and
marked 102. This pot is used to adjust the audio level to the right chan-
nel of the modulator IC. Seat it flat before soldering.
10. Install R4, another 1K ohm trimmer potentiometer. (marked 102).
This pot is used to adjust the audio level to the left channel of the modu-
lator IC.
11. Install C5, a .0047uF ceramic capacitor (marked 472).
12. Install C6, another .0047uF ceramic capacitor (marked 472).
13. Install R5 and R6, a 15K ohm resistor (brown-green-orange). These
resistors set the pre-emphasis characteristics for the FM10C at 75 uS for
use in the USA. Pre-emphasis is a technique used in FM transmitters to
increase the high frequency signal to noise ratio. For use in Europe and
other countries using 50 uS pre-emphasis use 10K resistors (brown-
black-orange).
Now we’ll install some electrolytic caps. Electrolytic capacitors have a
right and wrong way to be installed. Usually, these capacitors have a
wide stripe which indicates their polarity. Most of the time this stripe indi-
cates the negative lead. This can be verified by looking for the (-) sign in
the stripe. On rare occasions this stripe with have a (+) sign indicating a
positive polarity. The PC board or Parts Layout Diagram will show the
positive side of the capacitor's installation hole. Be sure to place the

FM10C 13
( + ) capacitor lead into the PC board ( + ) hole and the ( - ) lead into the
( - ) hole. Observe correct polarity when installing the electrolytic capaci-
tors.
14. Install C7, a 10 uF electrolytic capacitor. Watch that polarity!
15. Install C8, another 10uF electrolytic capacitor.
16. Install C10, yet another 10uF electrolytic capacitor.
17. Install J1, the left channel RCA-type PC-mount jack. After insuring
this parts sits flush on the circuit board be sure to solder the ground con-
nections well. They may require more heat but when working with RF, a
good ground is essential.
18. Install J2, the right channel RCA-type PC-mount jack.
Stereo Generator
19. Install X1, the small silver "can" crystal. Be especially careful when
installing this part as its leads are very small. This part location has four
holes on the circuit board. The leads of the crystal must be installed in
the two holes closest to the IC socket. A crystal has no polarity require-
ments so its leads can be placed in either of the two holes.
20. Install crystal strap, using a scrap component lead looped around
the crystal and placed through the other two crystal location board holes.
It is a good idea to solder the strap to the crystal after they have been
installed.
21. Install C11, a 10pF ceramic capacitor (marked 10).
22. Install C12, another 10pF ceramic capacitor (marked 10).
Power Supply Section
23. Install C15, a .001uF ceramic capacitor (marked 102).
24. Install VR1, the 78L02 +2 volt regulator. This part looks like a tran-
sistor and like a transistor, it must be place correctly to work. Follow the
parts layout diagram and PC board silkscreen for orientation. Solder all
three pins.
25. Install C3, a 100pF ceramic capacitor (marked 100 or 101).
26. Install S1, the DPDT push-button switch. You’ll want this part to be
seated correctly so that the power button moves freely when in the case.
Set it flush to the PC board before soldering all six pins.
27. Install C9, a 100uF electrolytic capacitor. Remember polarity!
28. Install C4, a 1000uF electrolytic capacitor. Polarity.

FM10A 14
29. Install L3, a 2.2uH inductor (red-red-gold). This part is located be-
tween L4 and the power jack J3.
30. Install C16, a .001uF ceramic capacitor (marked 102). This part is
near the audio section.
31. Install J3, the 2.1mm DC power jack. You can gently bend the leads
to keep this part from falling out of the board when you flip the board
over to solder it.
Multiplexer Balance
32. Install R7, another 100K ohm trimmer potentiometer. (marked 104).
Multiplexed Audio/Pilot
33. Install R9, a 4.7K ohm resistor (yellow-violet-red).
34. R8’s value will depend on the frequency band that will be used. It
will be calculated and installed in the next section.
35. Install C13, a 220pF ceramic capacitor (marked 221).
36. Install C14, a 10uF electrolytic capacitor. Remember polarity.
37. Install C21, a .001uF ceramic capacitor (marked 102).
RF Oscillator
38. Install C17, a .001uF ceramic capacitor (marked 102).
39. Install C19, a 10pF ceramic capacitor (marked 10).
40. Install shielded slug tuned coil L4. The larger tabs secure the shield
can to the ground foil connections, while the two thin leads are the coil
connections. If you find that the coil lead wires do not line up with the
PC board holes, simply "pull" the coil insert from the shield can, rotate it
a quarter-turn and insert back into the can. Make sure L1 is squarely
against the top of the PC board before soldering, solid installation of L1
is essential to the frequency stability of your transmitter.
41. Install C20, another 10pF ceramic capacitor (marked 10).
42. Install C26 a 1pF ceramic capacitor (marked 1). A via that connects
the ground plane on the top of the circuit board to the one on the bottom
is in the middle of C26’s pattern. Make sure to use the two outside holes
in this pattern.
43. C18’s value will depend on the frequency band that will be used. It
will be calculated and installed in the next section.

FM10C 15
RF AMP
44. Install R10, a 270 ohm resistor (red-violet-brown).
45. Install C22, a .001uF ceramic capacitor (marked 102).
46. Install R11, a 10K ohm resistor (brown-black-orange).
47. Install Q1, the transistor marked 2N2570. The flat side must be
placed as shown on the PC board. Mount it as close to the board as pos-
sible
48. Install R12, a 200 ohm 1/2 watt resistor (red-black-brown).
49. Install C25, a .001uF ceramic capacitor (marked 102).
RF Output
50. Install C23, a .001uF ceramic capacitor (marked 102). Make sure to
use the two outside holes in this pattern.
51. Install C24, the last .001uF ceramic capacitor (marked 102).
52. Install J4, the PC mount “F” connector. This is another part that you’ll
want to seat correctly before soldering or it won’t fit through the back
panel properly. Be sure to solder the ground connections well. .
53. Install R13, a 1K ohm resistor (brown-black-red).
54. Install L5, a 13 turn air core coil. Just as with the other inductors
polarity is not an issue.
55. Install ANT1, a telescoping antenna. Insert the screw from the bot-
tom side of the circuit board and tighten the screw using a #1 Phillips
screwdriver. The head of the screw should now be soldered to the pad
on the board. This allows the antenna to be remove easily without open-
ing the case.
56. Install U1, a BA1404 IC. Carefully insert the FM modulator IC into
the socket, taking care that all 18 pins get into their proper holes. The
orientation of the notched end, as shown on the Parts Layout Diagram is
critically important.
Battery Holder
57. Install the battery hold-down clamp, using a scrap component lead
looped through the PC board holes. Solder the pads on the board first
then square-up the clamp to the board and solder it to the looped wire.
58. Install the battery snap connector (without battery); The red wire is
positive and the black wire is negative.

FM10A 16
FM10C FREQUENCY RANGE SELECTION
Capacitor C18 sets the frequency range of the FM10C. R8 sets the pilot level
for the different bands. Values for C18 and R8 are as follows:
Desired Frequency of Transmission C18 Value R8 Value
Lower end of FM band (88-91 MHz) 27 pF 180K
Middle portion of FM band (90-97 MHz) 22 pF 220K
High end of FM band (95-108 MHz) 15 pF 470K
If you are not sure "where" you wish to place your FM transmitter in the FM
band, we suggest you solder an initial "trial" C18 capacitor and matching R8
resistor with a small amount of lead-length to spare, so that they are easy to
salvage and replace. This will enable you to properly test your FM10C and
then at a later point, you may change C18 and R8 as desired.
59. Install C18, either: 15 , 22 or 27 pf (marked 15, 22, or 27).
60. Install R8, either a 180K (brown-gray-yellow), 220K (red-red-yellow),
or 470K (yellow-violet-yellow) resistor.
That’s it! But before you grab the power supply and fire up the FM10C,
take a moment to check over your work. Check to be sure that all the
parts are installed and the polarity sensitive ones are placed properly.
Look for solder joints that could be questionable and need a quick touch-
up. Also look for potential solder bridges; the parts layout diagram can
help with that. You may want to hurry and get the kit powered up but any-
thing you find now will save you a lot more trouble later. Unless you like
the smell of smoke and the sound of things exploding! It’s worth the few
extra minutes. Looking over the PC board is the first step our Ramsey
technicians complete when testing units here at the shop.
CHOOSING AN OPERATION FREQUENCY
[A] It really is NOT sufficient to just "check" the FM band for an empty fre-
quency, using the FM portable radio closest at hand. It is your responsi-
bility to carefully research what FM stations can be listened to with a good
system within the transmitting range of your FM10C. This is especially
important in the low end of the FM broadcast band (88-92 MHz), where
there are numerous medium power National Public Radio stations per-
haps outside your own town, but which your neighbors may enjoy receiv-
ing, using a good receiver and outdoor antenna. Interfering with such re-
ception is a direct violation of federal law. The most reliable way of finding
a truly open frequency on the FM band is to check the band with a very
good FM receiving system using an external antenna. If you do not have
access to such a radio, most modern car radios (with exterior antenna)
are very sensitive and usable to help you know what stations your

FM10C 17
neighbors really can be receiving on a particular frequency.
[B] In choosing an operating frequency, remember that most "digital-tuning"
receivers, whether portable, mobile or hi-fi, are designed to tune in 200 KHz
increments and therefore might not receive well a signal operating between
these pre-tuned standard broadcasting frequencies. In order to comply with
Part 15 of FCC regulations, it is your responsibility to determine carefully that
your operation will not cause interference to broadcast reception. Please
study Appendix A of this manual before using your FM10C.
CASE ASSEMBLY
1. Place the case bottom (has four mounting holes for circuit board) in
front of you so that the tongue side is on the right and the groove side is
on your left.
2. Place the front panel in the groove of the case bottom in the side that
is facing you.
3. Place the circuit board in the case bottom so that the DPST switch
comes through the power hole of the front panel.
4. Lift the rear of the circuit board so that is at approximately a 45 degree
angle.
5. Place the rear panel over the jacks on the circuit board.
6. Drop the circuit board down while lining up the rear panel to the
grooves of the case bottom.
7. Install the four 4-40 x 3/8 screws through the circuit board securing it
to the case bottom. Do not over-tighten!
8. After doing transmitter alignments in the next section, place the top of
the case over the bottom so that the antenna goes through the pre-drilled
hole.
9. Line up the top with the sides of the case bottom, front, and rear pan-
els.
10. Secure the top to the bottom with the two 4-40 x 1-1/4 inch screws.
Again, do not over-tighten.

FM10A 18
FM10C REV2.1 SCHEMATIC DIAGRAM

FM10C 19

FM10A 20
ADJUSTING FM10C TRANSMITTER
Keep all tests very brief until you have carefully chosen an open operating
frequency in the FM broadcast band.
1. Transmitting Frequency:
After finding a suitable "open" frequency in the 88-108 MHz FM band, adjust
L4 with the plastic alignment screwdriver until you hear the carrier frequency
on a nearby FM radio. No audio input is needed to make this first adjustment,
you can simply listen for a "quieting" in the normal background noise "hiss."
2. Audio Connection:
Adjust both Left and Right level potentiometers (R3, R4) to full counter-
clockwise rotation. This is the minimum level position.
Connect the left channel only. Slowly increase R4 until a distortion is heard
in the right channel. Back R4 down slightly until distortion disappears. Re-
peat the process for the right channel and R3.
Hooking up an audio source to your FM10C is really quite simple. However,
there are some general rules:
 A terribly distorted sound is a sign of too much audio level. Simply ro-
tate the level potentiometers, R3 and R4, CCW to reduce the level.
Make sure you rotate each one about the same amount to maintain
proper stereo balance.
 Stereo LP turntables are low-level output and will require the use of a
preamplifier for proper audio input to the FM10C.
 NEVER connect the FM10C audio inputs to speaker outputs of a high
power stereo system; such a connection will destroy the IC chip.
 Consider using a mike mixer for professional "radio station" sound. It
will allow you to easily fade, mix and switch between various audio
sources.
3. Stereo balance:
Adjust R7 for correct stereo balance (near the middle of its range). The better
your ear for music and your understanding of quality audio devices and inter-
connections, the better will be the performance of your FM10C.