Vectronics VEC-1290K User manual

IIMPORTANT WARRANTY INFORMATIONI PLEASE READ
Return Policy on Kits When Not Purchased Directly From Vectronics: Before continuing any
further with your VEC kit check with your Dealer about their return policy. If your Dealer
allows returns, your kit must be returned before you begin construction.
Return Policy on Kits When Purchased Directly From Vectronics: Your VEC kit may be
returned to the factory in its pre-assembled condition only. The reason for this stipulation is,
once you begin installing and soldering parts, you essentially take over the role of the device's
manufacturer. From this point on, neither Vectronics nor its dealers can reasonably be held
accountable for the quality or the outcome of your work. Because of this, Vectronics cannot
accept return of any kit-in-progress or completed work as a warranty item for any reason
whatsoever. If you are a new or inexperienced kit builder, we urge you to read the manual
carefully and determine whether or not you're ready to take on the job. If you wish to change
your mind and return your kit, you may-but you must do it before you begin construction,
and within ten (10) working days of the time it arrives
Vectronics Warrants: Your kit contains each item specified in the parts list.
Missing Parts: If you determine, during your pre-construction inventory, that any part js
missing, please contact Vectronics and we'll send the missing item to you free of charge.
However, before you contact Vectronics, please look carefully to confirm you haven't misread
the marking on one of the other items provided with the kit. Also, make certain an alternative
part hasn't been substituted for the item you're missing. If a specific part is no longer
available, or if Engineering has determined that an alternative component is more suitable,
Vectronics reserves the right to make substitutions at any time In most cases these changes
Defective Parts: Today's electronic parts are physically and electrically resilient, and defective
components are rare. However, if you discover an item during your pre-construction
inventory that's obviously broken or unserviceable, we'll replace it. Just return the part to
Vectronics at the address below accompanied with an explanation. Upon receipt, we'll test it.
If it's defective and appears unused, well ship you a new one right away at no charge.
Missing or Defective Parts After You Begin Assembly: Parts and materials lost or damaged
after construction begins are not covered under the terms of this warranty. However, most
parts supplied with VEC kits are relatively inexpensive and Vectronics can replace them for a
reasonable charge. Simply contact the factory with a complete description. We'll process your
order quickly and get you back on track.
Factory Repair After You Begin Assembly: Kits-in progress and completed kits are specifically
excluded from coverage by the Vectronics warranty. However, as a service to customers,
technicians are available to evaluate and repair malfunctioning kits for a minimum service fee
of $18.00 ('/a hour rate) plus $7.00 shipping and handling (prices subject to change). To qualify
for repair service, your kit must be fully completed, unmodified, and the printed circuit board
assembled using rosin-core solder. In the event your repair will require more than an hour to
fix (or 536.00, subject to change), our technicians will contact you in advance by telephone
before performing the work. Defective units should be shipped prepaid to:
Vectronics
300 Industrial Park Road
Starkville, MS 39759
When shipping, pack your kit well and include the minimum payment plus shipping and
handling charges (525.00 total). No work can be performed without pre-payment Also,
p
rovide a valid UPS return address and a da
y
time
p
hone number where
y
ou ma
y
be reached.

VEC-1290K Instruction Manual AM Radio Transmitter
INTRODUCTION
Own and operate your own low-cost AM broadcast station! You're the disc
jockey or talk show host-play music from your CD player, tape deck or other
audio source. Play vintage radio show cassettes on your favorite antique radios!
The VEC-1290K is easily setup to broadcast a High-Fidelity signal in the AM
broadcast band between 540 and 1710 kHz-find a clear frequency and broadcast
interference free to your neighbors! The transmitter is fully compatible with
either 9-kHz European or 10-kHz American channel spacings! Accepts audio
from standard line-level or microphone-level sources. True high-level Class C
modulation delivers good modulation depth and linearity. No FCC license is
required, its perfectly legal under Part 15 of the FCC rules. This Vectronics kit
features a professional quality epoxy PC board, with solder mask and silk-
screened parts legend to make assembly a breeze!
TOOLS AND
Construction Area: Kit construction requires a clean, smooth, and welllighted
area where you can easily organize and handle small parts without losing them.
An inexpensive sheet of white poster board makes an excellent construction
surface and provides protection for the underlying table or desk. Well-diffused
overhead lighting is a plus, and a supplemental high-intensity desk lamp is
especially helpful for close-up work. Safety is always important! Be sure to use
a suitable high-temperature stand for your soldering iron, and keep the work
area free of combustible clutter.
Universal Kit-building Tools: Although your particular kit may require
additional items for completion, virtually all construction projects require a
work area outfitted with the following tools and supplies:

BEFORE YOU START BUILDING
Experience shows there are four common mistakes builders commonly make.
Avoid these, and
y
our kit will
p
robabl
y
work on the first tr
y
!
1. Installing the Wrong Part: It always pays to double-check each step. A 1K
and a IOK resistor may look almost the same, but may act very differently in
an electronic circuit! The same is true for capacitors-a device marked 102 (or
.001 uF) may have very different operating characteristics from one marked
103 (or .01 uF).
2. Installing Parts Backwards: Always check the polarity of electrolytic
capacitors to make sure the positive (+) lead goes in the (+) hole on the
circuit board. Transistors have a flat side or emitter tab to help you identify
the correct mounting position. ICs have a notch or dot at one end indicating
the correct direction of insertion. Diodes have a banded end indicating correct
polarity.
3. Faulty Solder Connections: Inspect for cold-solder joints and solder
bridges. Cold solder joints occur when you don't fully heat the connection
or when metallic corrosion and oxide contaminate a component lead or
pad. Solder bridges form when a trail of excess solder shorts pads or
tracks together (see Solder Tips below).
4. Omitting or Misreading a Part: This is easier to do than you might think!
Always double-check to make sure you completed each step in an assembly
sequence.
Soldering Tips: Cleanliness and good heat distribution are the two secrets of
professional soldering. Before you install and solder each part, inspect leads
or pins for oxidation. If the metal surface is dull, sand with fine emery paper
until shiny. Also, clean the oxidation and excess solder from the soldering
iron tip to ensure maximum heat transfer. Allow the tip of your iron to
contact both the lead and pad for about one second (count "one-thousand-
one") before feeding solder to the connection. Surfaces must become hot
enough for solder to flow smoothly. Feed solder to the opposite side of the
lead from your iron tip. Solder will wick around the lead toward the tip,
ill df
Desoldering Tips: If you make a mistake and need to remove a part, follow
these instructions carefully! First, grasp the component with hemostats or
needle-nose pliers. Heat the pad beneath the lead you intend to extract, and,
pull gently. The lead should come out. Repeat for the other lead. Solder may

VEC-1290K Instruction Manual AM Radio Transmitter
Kit
fill in behind the lead as you extract it-especially if you are working on a
double-sided board with plate-through holes. Should this happen, try heating
the pad again and inserting a common pin into the hole. Solder won't stick to
the pin's chromium plating. When the pad cools, remove the pin and insert the
correct component. For ICs or multiple-pin parts, use desoldering braid to
remove excess solder before attempting to extract the part. Alternatively, a
low-cost vacuum-bulb or spring-loaded solder sucker may be used. Parts
damaged or severely overheated during extraction should be replaced rather
than reinstalled.
Work Habits: Kit construction requires the ability to follow detailed
instructions and, in many cases, to perform new and unfamiliar tasks. To avoid
making needless mistakes, work for short periods when you're fresh and alert.
Recreational construction projects are more informative and more fun when
you take your time. Enjoy!
Sorting and Reading Resistors: The electrical value of resistors is indicated by
a color code (shown below). You don't have to memorize this code to work
with resistors, but
y
ou do need to understand how it works:
When you look at a resistor, check its multiplier code first. Any resistor with a
black multiplier band falls between 10 and 99 ohms in value. Brown designates
a value between 100 and 999 ohms. Red indicates a value from 1000 to 9999
ohms, which is also expressed as 1.0K to 9.9K. An orange multiplier band
designates 10K to 99K, etc. To inventory resistors, first separate them into
groups by multiplier band (make a pile of 10s, 100s, Ks, 10Ks etc.). Next, sort
each group by specific value (1K, 2.2K, 4.7K, etc). This procedure makes the
inventory easier, and also makes locating specific parts more convenient later
on during construction. Some builders find it especially helpful to arrange
resistors in ascending order along a strip of double-sided tape.
This VEC kit contains molded chokes which appear, at first glance, similar to
resistors in both shape and band marking. However, a closer look will enable
you to differentiate between the two-chokes are generally larger in diameter

VEC-1290K Instruction Manual AM Radio Transmitter Kit
and fatter at the ends than resistors. When doing your inventory, separate out
an
y
chokes and consult the
p
arts list for s
p
ecific color-code information.
Reading Capacitors: Unlike resistors, capacitors no longer use a color code
for value identification. Instead, the value, or a 3-number code, is printed on
the body.
Value Code
10 pF = 100 Multilayer
100
p
F = 101
(
270
p
F
)
1000 pF
=
102
.001 uF = 102*
.01 uF = 103
.1 uF = 104
As with resistors, it's helpful to sort capacitors by type, and then to arrange
them in ascending order of value. Small-value capacitors are characterized in
pF (or pico-Farads), while larger values are labeled in uF (or micro-Farads).
The transition from pF to uF occurs at 1000 pF (or .001 uF)*. Today, while
most monolithic multilayer and disc-ceramic capacitors are marked with a
three-number code, you may still find a .1 uF capacitor marked either "104"
or ".1". For three digit codes, the first two digits indicate a numerical value,
while the last digit indicates a multiplier (same as resistors). The value is in
pF; thus a capacitor marked "104" is 100,000 pF, or. 1 uF.
Electrolytic capacitors are always marked in uF. Electrolytics are polarized
devices and must be oriented correctly during installation. If you become
confused by markings on the case, remember the uncut negative lead is
slightly shorter than the positive lead.
Integrated Circuits: Proper IC positioning is indicated by a dot or square
marking located on one end of the device. A corresponding mark is silk-
screened on the PC board and printed on the kit's parts-placement diagram. To
identify specific IC pin numbers for testing purposes, see the diagram below.
Pin numbers always start at the keyed end of the case and progress
counterclockwise around the device, as shown:

VEC
-
1290K Instruction Manual AMRadio Transmitter
PARTS LIST
Your kit should contain all of the parts listed below. Please identify and
inventory each item on the checklist before you start building. If any parts are
missing or damaged, refer to the manual's warranty section for replacement
instructions. If you can't positively identify an unfamiliar item on the basis of
the information given, set it aside until all other items are checked off. You
may then be able to identify it by process of elimination. Finally, your kit will
go together more smoothly if parts are organized by type and arranged by
value ahead of time. Use this inventory as an opportunity to sort and arrange
parts so you can identify and find them quickly.
Resistors:
Q Qty Part Description Designation
1 15 ohm (brown-green-black) R2
1 1K ohm (brown-black-red) R3
14.7Kohm
(y
ellow-violet-red
)
R4
Ca
p
acitors:
Q Qty Part Description Designation
2 100 pF ceramic disc (101) C9,C10
1 510 pF polstyrene (510) C8
5 0.1 uF ceramic disc (104) C3,C4,C5,C6,C7
2 100 pF ceramic trimmer CI 1,C12
Semiconductors:
Q Qty Part Description Designation
1 4049 16-pin DIP integrated circuit U1
1LM3868-
p
in DIP inte
g
rated circuit U2
Inductors:
[X] Qty Part Description Designation
1 22 uH molded choke (red-red-black) L2
2 100 uH molded choke (brown-black-brown) L7,L8
2 180 uH molded choke (brown-gray-brown) L5,L6
2 330 uH molded choke (orange-orange-brown) L4,L9
1 680 uH molded choke (blue-
g
ra
y
-brown) L3

VEC-1290K Instruction Manual AM
Switches/Jacks/Misc.:
0 Qty Part Description
Radio Transmitter
KitDesignation
1
DPDT
p
ush-action switch SW1
1 RCA phono jack, PC-mounted J1
1 2.1 mm DC coaxial power jack J2
5 2-pin PC board mount headers JMP1,2,3,4,5
2 2-pin jumpers, shorting
116-pin IC socket
18-
p
in IC socket
1 4" nylon cable tie
1PCboard
1 6' length of insulated 20-AWG solid wire ANTI
PARTS PLACEMENT DIAGRAM

VEC-1290K Instruction Manual AM Radio Transmitter Kit
STEP-BY-STEP ASSEMBLY INSTRUCTIONS
Before assembling your kit, please take time to read and understand the VEC
kit warranty printed on the inside cover of this manual. Read through the
assembly instructions to make sure the kit does not exceed your skill level.
Once construction is started, the kit is non-returnable. Finally, if you haven't
already done so, please verify that all parts listed in the inventory are included.
If anything is missing or broken, refer to the warranty instructions for
replacing missing or damaged parts.
First, a few notes and comments to help you along. Part designators for
components such as R1, C3, etc., appear on the silk-screened legend on the
component-mounting side of the printed circuit board. These correspond to
the drawing shown in PARTS PLACEMENT section of this manual. The parts
are inserted on the silk-screen side of the board. All capacitors should be
installed with their bodies as close to the PC board as possible; this is very
im
p
ortant in RF circuits.
If you have last-minute questions concerning what tools or materials are
needed to assembly this kit, please refer back to the section entitled BEFORE
YOU BEGIN.
"Install" When you are directed to install a part, this means to locate, identify,
and insert the part into its mounting holes on the PC board. This includes pre-
bending or straightening leads as needed so force is not required to seat the
part. Once a component is mounted, bend each lead over to hold it in place.
Make sure trimmed leads don't touch other pads and tracks, or a short circuit
may result:
Not Good
"Solder" When you are directed to solder, this means to solder the part's leads
in place, and to inspect both (or all) solder connections for flaws or solder
bridges. If no soldering problems are noted, nip off the excess protruding
leads with a sharp pair of side cutters.
Phase 1: Resistors
Begin assembly by installing the '/,-watt fixed resistors. Because these are all
5-percent tolerance ending with a fourth gold color band, you need only read
the first three bands of the color code during the following steps. All resistor

VEC-1290K Instruction Manual AM Radio Transmitter
leads should be formed as shown below. Install and solder resistors at the
followin
g
locations:
Important Note: the fourth resistor color band is for tolerance, and is not called
out in the followin
g
ste
p
s.
1. Find the 15-ohm (brown-green-black) '/,watt resistor.
2. Install the 15-ohm resistor at R2 on the printed circuit board.
3. Solder and trim the leads.
4. Find the 1K-ohm (brown-black-red) 1/4-watt
resistor. 5. Install and solder at R3.
6. Find the 4.7K-ohm (yellow-violet-red) '/.-watt
resistor. 7. Install and solder at R4.
resistor
9. Check each solder joint. Look for solder splashes, bridges (a bridge is
where solder has made a connection between two or more points
that should not be connected
)
, or
p
oor solder connections.
Phase 2: Jum
p
er Headers
[ ] [ ] 1. Locate the five 2-
p
in
j
um
p
er headers.
Short pins into
pc
O O board holes

VEC
-
1290K Instruction
Important Note: When installing the two-pin jumper headers, the shorter pins
are inserted into the
p
c board.
,
10. Locate the two 100-pF ceramic trimmer capacitors. When inserting,
ensure that the three component leads are fully seated and that the
capacitor body is level. Install and solder at the following locations:
11. C11 100
-
pF trimmer
12. C12 100-
p
F trimmer
13. Locate the 510-pF polystyrene capacitor. This part may be
marke 511
,
or with 510 usin
g
the old markin
g
code s
y
stem.
14. Install and solder the 510-pF (510 or 511) polystyrene capacitor al
C8
.
10

VEC-I290K Instruction Manual AM Radio Transmitter
Phase 4: Molded choke installation
Important Note: only the first three color bands are specified in the following
directions. The fourth band is for tolerance and ma
y
be disre
g
arded.
1. Locate the 1000-uH molded choke (brown-black-red). Install and
solder at location L1.
2. Locate the 22-uH molded choke (red-red-black). Install and solder at
location L2.
3. Locate the 680-uH molded choke (blue-gray-brown). Install and solder
at location L3.
4. Locate the two 330-uH (orange-orange-brown) molded chokes. Install
and solder at locations:
5. L4 330 uH
(
oran
g
e-oran
g
e-brown
)
.
6. L9 330 uH
(
oran
g
e-oran
g
e-brown
)
.
7. Locate the two 180-uH (brown-gray-brown) molded chokes. Install and
solder at the following locations:
8. L5 180 uH (brown-gray-brown).
9. L6 180 uH (brown-gray-brown).
and solder at the followin
g
11. L7 100 uH
(
brown-black-brown
)
.
12. L8 100 uH
(
brown-black-brown
)
.
rnase 5: IC Sockets/ICs
1. Locate the 8-pin DIP IC socket. Note that the socket is "keyed", and
should be installed with its key aligned to the silk-screened outline
on the PC board.
1 2 3 4 Pin
Numbers
To
p
view o
f

VEC
-
1290K Instruction Manual AM Radio Transmitter
2. Locate the 2N3904 plastic transistor. Form its leads so it sits close
to the board at location Q1. Note that the device has a rounded and
flat side. Align the package to conform to the silk-screened legend.
Solder and trim.
Phase 7: Electrol
y
tic Ca
p
acitors
Electrolytic capacitors are polarized devices, and must be inserted with
respect to polarity. The style used in the VEC direct conversion receivers
have radial leads; both leads exit from one end of the device body. Each
capacitor's plus (+) mounting holes are noted both on the circuit board and
parts placement diagram. If the markings on the capacitor body are unclear,
the plus (+) lead is the longer of the two.
1. Locate the two 10-uF electrolytic capacitors. Install and solder at
the
following locations. Observe the polarity markings!
2. C1 10uF
3. C2 10
Phase 8: The Finishin
g
Touches
1. Locate the IOK-ohm vertical trimmer resistor. Install at location RI.
Be sure the
p
ot is full
y
seated to the board
,
and solder the three leads.
2. Locate the RCA PC-board mount phono jack. Install at location Jl. Be
sure the jack is fully seated, solder.
3. Locate the 2.lmm coaxial power jack. Install at location J2. Be sure
the jack is fully seated, solder.
4. Locate the six-foot len
g
th of white insulated 20-AWG antenna
5. At one end, strip '/a" of insulation from the wire.
1

VEC
-
1290K Instruction Manual AM Radio Transmitter Kit
7. Find the 4" nylon wire tie. Secure the antenna wire to the PC board
using the wire tie as shown below. Pull the tie wrap tight, and trim
excess tie len
g
th.
8. Locate the two plastic shorting jumpers. Put these in the parts bag
until needed for the ali
g
nment
p
rocedures.
9. This completes the assembly of the VEC-1290K AM radio transmitter.
Please go over the board and verify that all parts are properly
installed. Check all solder connections, and redo those that look
suspect.
TESTING AND ALIGNMENT
Before attempting any adjustments, the entire section dealing with Alignment
and Testing should be read, and some familiarity with the Operating
Instructions section is also advisable. The transmitter requires a suitable
external power and audio source for alignment and operation.
Initial alignment sets the transmitter to the desired operating segment of the
AM broadcast band. The VEC-1290K oscillator stage covers the AM band in
three preset ranges. These are determined by the presence or absence of a
jumper at locations JMP1 and JMP2. Fine tuning within each of the
three ranges is set by trimmer capacitor C12.
Oscillator frequency ran 'reset,
540kHz to 870kHz no jumper
870kHz to 1420kHz JMP1
1 l70kHz to l7l0kHz
r
Table 1
1

1

1
'
EC
-
1290K Instruction Manual AM Radio Transmitter
clip on JMP 1. Capacitor C 12 will now tune the transmitter frequency from
870 to 1420 kHz.
A frequency counter is the quickest method to set the transmitter precisely on
channel. Attach the counter input to either side of resistor R3. The signal is
strong enough at this point to drive any 50-ohm or high-impedance counter
without problem.
A portable radio can also be used. Set the radio to the clear frequency, and
apply an audio source to the transmitter. (This is discussed in the OPERATING
INSTRUCTIONS section.) Slowly tune C12 until the transmitter is heard on the
radio.
Hint: Store unused shorting clips where they won't become lost. Place unused
shortin
g
cli
p
s over one
p
in o
f
o
p
en
j
uni
p
ers.
Antenna Matchin
g
:
Important Note: For reasons given later, the transmitter is designed to be
operated only with the supplied 6-foot antenna wire. Attempting to use other
antennas will result in a severe mismatched condition, reduced range and
distorted audio. The antenna wire should be run out straight, avoiding
proximity to nearby metal objects. If more range is needed, try relocating the
transmitter to a different location.
Once a clear channel has been found, and the oscillator set to frequency, the
antenna matching network must be tuned. Refer to Table 2. Note that some
frequencies, such as 800 kHz, can be matched by one of two possible jumper
configurations. Try both, and use the one which works best. Using the previous
example where the oscillator was set to 910 kHz, Table 2 shows the proper
antenna match range is selected by placing a shorting clip across the pins of
JMP4. (910 kHz falls between 730 kHz and 1400 kHz.)
When the proper antenna matching range has been set, capacitor CI I is tuned
for maximum radiated signal. This can be done by carefully adjusting CII while
increasing the distance between the transmitter and a portable radio. As the
signal grows weaker with distance, adjust CI I for the loudest signal.
If
y
ou have access to test e
q
ui
p
ment
,
the followin
g
ste
p
s ma
y
also be
Using an oscilloscope: If your oscilloscope has a vertical amplifier with
useable bandwidth to at least 2 MHz, you may attach the probe to the junction
of ANT 1, C 1 I and L6 as shown on the schematic. C 11 should be peaked for
maximum scope amplitude. A low-capacitance 10:1 probe is recommended to
avoid detuning.
1

VEC
-
1290K Instruction Manual AM Radio Transmitter
Using afield strength indicator: If you have a general purpose volt-ohmmeter,
the schematic below shows a simple and easily constructed RF field strength
meter. Most of the parts can be found at Radio Shack. Assembly is not critical
due to the ver
y
low o
p
eratin
g
fre
q
uencies.
The diode must be a germanium type. The 3-foot wire "antennas" should be
run near the VEC-1290K transmitter antenna. Adjust C11 for a maximum DC
voltage reading on the voltmeter. Keep the field strength meter pickup antenna
wires as far from the transmitting as possible to prevent interaction. Use the
lowest DC voltage setting on the voltmeter for maximum sensitivity. Some
voltmeter test lead jacks may allow the diode leads to be slipped between the
test lead plugs and meter jacks-if so, the meter leads may be spread apart and
used as the pickup antenna.
Audio Gain Settin
g
:
The VEC-1290K will accommodate a wide range of audio levels, from "line level"
cassette or CD deck feeds, or even the very low output from a local mike.
Removing capacitor C2 will reduce the amplifier gain; this is the preferred
configuration for usually high line-level audio sources such as when taking an
audio feed directl
y
from a s
p
eaker out
p
ut.
Setting the gain control. The gain control sets the modulation percentage.
Setting the gain control too high results in over modulation and considerable
audio distortion The proper setting for the gain control RI can be found by
starting at it lowest setting, and with an audio source connected, slowly
increasing the gain the control until the audio starts to sound raspy or clipped.
Once clipping is heard, the control setting should be reduced until the
distortion,goes away. This is most noticeable on music sources. Experienced
technicians may use an oscilloscope to observe the RF modulation envelope for
clipping, but those procedures are beyond the scope of this manual.
1

VEG1290K Instruction Manual AM Radio Transmitter
The VEC-1290K should be mounted in an enclosure. Vectronics has design a
matching enclosure for the VEC-1290K. The matching enclosure is anal metal
box which includes knobs, hardware, decals, and rubber feet. (Model VEC-
1290KC.) If you wish to supply your own, RadioShack offers several styles that
are suitable for this
p
ur
p
ose.
Power requirements: The VEC-1290K operates from an external 12-volt D
source and draws about 100 mA. Wall-plug power supplies are an ideal sour of
p
ower
,
but should have the followin
g
s
p
ecifications:
1. Internall
y
f
iltered and re
g
ulated 12-volt DC
2. Rated for at least 300 mA continuous
3. Be e
q
ui
pp
ed with a 2.1 mm coaxial
p
ower
j
ack, center
p
in
The VEC-1290K can be operated at lower supply voltages down to about 9
volts, but the transmitter range will be reduced. The transmitter is powered
when the SW1
p
ush shaft is in the de
p
ressed
p
osition.
Once set to frequency, and the antenna tuned, the only control that needs be
set is the audio level (trimmer potentiometer R1).
Your home studio: The VEC-1290K will accommodate various sources of
audio-CD players, tape or cassette decks, or even a local microphone for the
budding DJ or talk show host. Unless a single audio source is going to be used,
the audio gain control R1 will have to be continuously adjusted for each new
audio source. Tape decks and cassette players provide "line level" audio outputs
for interconnections between decks and amplifiers. Microphone produce much,
much lower signal levels. As mentioned in the alignment section, capacitor C2
should be removed when using speaker level audio feeds.
Using a "mixer": To give your home station that "pro" sound, an inexpensive
four or five channel mixer may be used between the various audio sources and
the transmitter audio input. The mixer will allow the level for each source to be
set individually so all of your audio feeds will be balanced when played on the
air. The mixer master output can be used to set the modulation limits. The level
controls can be used to "fade" into one source from another, just like disc
jockies do on the air! You can also use an inexpensive graphic equalizer to tailor
your station's on-the-air sound-but the VEC-1290K as-is rivals the fidelity of
man
y
FM broadcast stations!
Other uses: Let your imagination be your guide! We know of one VEC-1290K
that is being used on a DSS satellite system to play the MusicChoic6m Big
Band music channel to vintage AM radios throughout the housel

VEC-1290K Instruction Manual AM Radio Transmitter
Getting the most range: The transmitter antenna system is most efficient at the
higher frequencies. The new expanded AM broadcast band between 1610 and
1710 kHz is still relatively free of new station assignments. Likewise, many
VEC-1290K's will make it down to as low as 530 kHz, a relatively quiet
frequency in most areas.
Try to locate the VEC-1290K transmitter in area that is free of metal support
structures. Remember that the VEC-1290K may be remotely located; use
shielded audio cable to run between the transmitter audio input back to the
"station" location. Another "trick" you may try is attaching a good ground to
the transmitter cabinet. This will improve the antenna radiation efficiency.
Always run the six-foot antenna wire in a straight line, never coiled or zig-
zagged.
Understandin
g
the FCC rules:
Federal Communication Commission (FCC) rules and regulations governing
unlicensed AM broadcast transmitters are complicated and technical. Devices
such as the VEC-1290K AM transmitter are covered under Part 15 of the FCC
rules and regulations.
Part 15 rules permit a maximum field strength of 24000/fkHzuV-per-meter at
30 meters, between 510 kHz and 1710 kHz. The rules also permit a 100-mW
transmitter with a ten-foot antenna, including the feedline. In order to meet Part
15 regulations, the transmitter output must be kept below 2 volts rms when
using a 50-ohm antenna. The high-impedance antenna and power level of the
VEC-1290K meet FCC Part 15 requirements.
Your responsibilities under Part 15. Unlicensed devices operating under Part
15 must not cause interference, and must accept interference as a part of their
operation. What does this mean in plain English? If your station is causing
interference to the reception of a licensed broadcast station in your neighbors'
radios, you are in violation of FCC rules and are operating illegally. Either
operation must be suspended, or a new clear frequency found. If
broadcast stations are interfering with your broadcasts, this is something you
must accept being a micro-broadcaster under FCC Part 15 regulations. .
Here are some
g
uidelines to
1. Identify your station regularly, stating your location and purpose. Do not
make up FCC call letters! You can use an ID along the lines of "This is
Radio 910, operating from New York City".
2. Never transmit false distress si
g
nals!
3. Avoid
p
rofanit
y
or indecenc
y
.