provides these antenna plans as a courtesy to our customers who want to
experiment with a high performance antenna. Construction, installation, and
use of this antenna is solely at your own risk. SSTRAN can not be held
liable for any personal injury, property damage, or any other legal
liabilities that you may incur at any time during the construction,
installation, or use of this antenna.
1. As with any DIY project
using hand tools, power tools and chemical products, there is always a risk
of personal injury. Read and understand the safety notices that are
included with all tools and chemical products that you use.
2. Installation of this
antenna may present a risk of electric shock injury or electrocution.
You must take all precautions to ensure that the antenna and any connecting
wires will not come in contact with a live electric wire while maneuvering
the antenna into position during installation. You must also ensure that no part of the antenna will contact
a live electric wire in the event that the antenna becomes dislodged from
its mounting position for any reason at any time.
3. As with any outdoor
antenna, there is always the risk of lightning damage. For your safety, and
to reduce the risk of damage to your home or property, ensure the
transmitter is properly grounded.
1. Check your local
ordinances and covenants to ensure that your antenna installation complies
with any rules that may be in effect that restrict the size, height, and
location of outdoor antennas.
2. When constructed
according to the plans, this antenna will comply with the generally
accepted interpretation of FCC Part 15 section 15.219 governing antenna
dimension restrictions . Be aware
that the FCC can order you to cease operations if you cause interference to
any commercially licensed station. You will reduce your likelihood of
receiving an FCC order if you build the antenna as described, choose an
unused frequency in your area, and operate your station in a civil manner.
The AMT3000 transmitter must
be modified according to the instructions given in Required AMT3000
Circuit Modifications. These modifications are simple, but very
important. This antenna will not perform properly without the
Thanks to more customer comments, steps 1, 8 and 9 under
"Winding The Coil" were corrected.
Thanks to customer comments, the antenna plans have been
refined to somewhat simplify construction. The new version will perform
exactly the same as the original version. If you are currently constructing
the original version or want to reference the original version you can
access the plans here: original
A well constructed tuned vertical antenna is a must for getting
maximum range from your Part 15 AM transmitter. The FCC restricts the total length of the antenna, feed line,
and ground lead to 3 meters (118 inches).
This is very short at AM broadcast band frequencies. Because of this restriction, even the best
Part 15 compliant antenna will not be very efficient compared to those big
commercial broadcast station towers. Because the feed line length is included
in the total length, the transmitter must be mounted at the base of the
antenna in a weatherproof enclosure.
The antenna described here is
designed to be rugged and stable in an outdoor environment. All materials are readily available from
your local home improvement store (Home Depot, Lowes, Sears Hardware) and
from electronics mail order suppliers (Mouser Electronics). You should be reasonably handy with hand
tools and an electric drill. You also
will need to do a couple of copper pipe "sweat" solder joints using
a small propane torch and a few PVC solvent weld joints.
The antenna tuning range is
restricted to 1500 kHz - 1700 kHz to make it simpler to construct.
For best results your antenna
should be elevated by 20-25 feet, but you can still get good performance by
mounting it on a pipe near ground level.
Be sure to consider that you will need to access to the bottom portion
of the antenna and the transmitter for tuning after installation.
Familiarize yourself with the
antenna drawing and parts list: Drawing and Parts
List and procure any parts that you need. If you have ever done any plumbing around the house, you may
already have some of these parts.
If you don't have experience
with solvent-welding PVC pipe fittings or soldering copper pipe fittings,
click on the links to the left for some simple guidance.
Power and Audio Cables
The power and audio cables will need to be long enough to
reach the transmitter at its final installation location.
You can extend the 18 VAC wall transformer output wire by
fabricating an extension from readily available parts. Obtain one 2.1 mm
power plug (female) and one 2.1 mm power socket (male) from RadioShack. Most
any two conductor wire will work because the current draw is small. A length
of lightly insulated lamp cord will work as long as the insulated wire will
fit into the plastic handle of the 2.1 mm plug. Solder the plug and jack to
the ends of the two conductor wire. Polarity is not important.
Obtain audio cables that will be just long enough to reach
the transmitter in its final installation location. You can join shorter
cables with female-to-female adapters.
If the adapters will be outside, be sure to tape them well to seal out
moisture. Long audio cables will
attenuate higher audio frequencies. You can compensate by driving the audio
from a low impedance source such as the 8 ohm speaker output terminals of a
stereo amplifier. Make sure the
Treble Boost jumper plug (S6) on the transmitter board is installed in the
shorted position. You may also want
to add treble boost to your audio source signal.
Fabricating The Loading Coil
This is the most time
consuming step. The coil is made by
wrapping #16 Nysol insulated wire in a tight spiral around a section of
3" white schedule 40 PVC pipe.
However, tapping points must be formed at every other turn near one
end of the coil, making the winding process a little more complicated. Note that the outside diameter of the
3" PVC pipe is actually 3 1/2".
The 3" nominal size refers to the inside diameter.
Do not use gray or black PVC
pipe for the coil. Use only white
schedule 40 PVC. Gray and black PVC may
be formulated with carbon pigment, which can cause coil losses to be higher.
Preparing The PVC Pipe Before Winding The
PVC pipe cutters are available, but are expensive. PVC can be easily cut with a hacksaw. A 24-tooth blade will make a nice cut. Use a miter box or other suitable method
for guiding the blade to get a square cut.
Or, you can mark the cut line with a pencil around the circumference,
and make partial cuts incrementally around the circumference to avoid
drifting off the line. Use sandpaper
to remove outside burrs.
by cutting an 11" section of 3" white PVC pipe (ref. 16).
medium-grit sandpaper to sand the entire outside surface until all lettering
is removed and the surface is no longer shiny.
the pipe 2 inches in from each end and wrap masking tape around the pipe at
the marks so that the pipe is exposed
between the marks. Coat the entire 7
inch long exposed area with exterior grade varnish to seal the pipe and keep
it from absorbing moisture (PVC tends to absorb moisture over time which can
lead to higher coil losses).
the varnish dries, use a fine-tipped
felt marker and a straight-edge to draw a single straight reference line from
one end of the pipe to the other, parallel to the sides of the pipe.
the reference line, mark and drill a
3/32" diameter hole 3" from one end. Now mark and drill a second 3/32" diameter hole 1/2" to either side of the first and at the
same 3" distance from the end of the pipe. These two holes will secure the wire while you wind the coil.
Winding The Coil
You will now begin winding
the coil, but first some important points. The coil must be wound
tightly. There must be no space
between turns. Be careful to avoid
kinking the wire. Carefully
straighten any kinks as you go along.
This is fairly stiff wire and
will spring outward if you don't maintain constant tension on the wire while
winding. Cut a bunch of 2" long
strips of plastic electrical tape before you start. Keep them handy to put on the coil at various places as you
wind to hold the wire in place. There
will be a total of 87 turns in the coil.
You should apply a strip of tape to the coil about every 5 turns or so
to prevent the coil from springing out if you relieve the tension at any
time. After winding is complete, you
will be drilling two more holes to secure the wire at the far end. Once the wire is secured tightly through
these holes, you can safely remove all the tape strips.
To avoid kinking the wire, it
must be unrolled from the spool as you roll it onto the pipe. Place the spool of wire on a dowel or
metal rod that is secured in a vise, or C clamp, in a vertical position. Devise a method for putting some drag on
the spool to keep the wire in tension as you wind. One way to do this is to clamp the dowel somewhat off-vertical
so the spool tends to bind slightly against the top of the vise as you unwind
some wire from the end of the spool and insert the end about 12" into
the hole that is on the reference line.
Using pliers, form the wire protruding inside the pipe into a U shape
and feed it back out through the second hole. Keep forming and pulling the wire out until the wire is snug
against the inside of the pipe between the holes. Bend the length of the wire that now protrudes outside the pipe
toward the closest end of the pipe to keep it out of the way while you wind
it doesn't matter which direction you wind the coil. Choose a direction that is comfortable for
63 full turns of wire, tight and closely spaced around the PVC pipe. Secure this part of the coil well with
tape before continuing to wind the rest of the coil.
Beginning at turn 63, you
will be forming a tap point every other turn for the remainder of the winding
process. A tap is formed by bending
the wire with pliers to form a small "U" or hump in the wire. The hump should be about a quarter inch
wide and about a quarter inch high.
These measurements aren't critical.
The objective is to form the wire out away from the pipe sufficiently
to allow clearance for soldering a wire to the tap.
Before forming each tap, the
wire needs to be tinned with solder for a total length of about 1"
(1/2" on either side of the center of the tap). The wire has an insulating coating. If you purchased the recommended Nysol
insulated wire, you may be able to solder directly to the wire with a high
wattage iron without first stripping the insulated coating. Test this by attempting to apply solder to
the end of the short piece of wire protruding from the pipe at the start of
the winding. It helps to scrape away
a small area of the coating down to bare copper to aid heat flow to the
wire. Start heating at the bare
copper and flow a blob of solder onto the wire. Move the iron and solder blob slowly along the wire until the
Nysol coating begins to bubble and the solder adheres evenly to the
wire. If you are not satisfied with
the results, you will need to thoroughly scrape away the coating all around
the wire with a sharp knife before applying solder.
Taps should be staggered
about a half inch each side of the reference line to make it easier to make a
connection without shorting to adjacent taps. Begin with the peak of the first tap hump positioned 1/2"
before the reference line, then position the next tap hump peak 1/2" after the reference line, and so
the first tap at turn 63 (reference line minus 1/2").
two full turns and form a tap that is staggered from the previous tap
(reference line plus 1/2").
step 5 until you have a total of 12 taps staggered alternately before and
after the reference line. The last
tap should be at the 85 turn point.
the last tap, continue to wind 2 more turns to the reference line.
the wire with about 2" excess after the reference line. Secure the wire
well with tape while you drill two more holes. This wire will be connected to the antenna pipe clamp in a
you did at the beginning of the coil, drill two 3/32" holes at the end
of the coil, one on the reference line and one 1/2" beyond the reference
line. Insert the wire end into the
hole on the reference line and back out the other hole. Cut the wire that now
protrudes out to about 1/2". Then scrape and tin the end. This end wire
is at turn 87 and will serve as the final "tap" point.
10. Now that the
wire is secured at both ends of the coil, you can remove all the tape strips.
11. Coat the outside
of the coil with a second coat of exterior grade varnish taking care not to
get varnish on the wire ends or on the taps
Coat just the coil, not the unvarnished ends of the plastic pipe.
12. After the second
coat of varnish dries, remove the masking tape and cement the 3" PVC
pipe caps (ref. 15) onto the ends of the coil pipe. See Solvent Welding PVC Joints for PVC pipe
Antenna Construction Steps
First, some notes on cutting
copper pipe. The best way to cut
copper pipe is with a wheel-type tubing cutter. A cutter that can handle up to 3/4 in. pipe is inexpensive and
worth purchasing at a home improvement store
Copper pipe can also be cut with a fine-tooth hack saw. Be careful while cutting copper pipe with
a hacksaw so as not to deform the circular shape of the pipe. Don't bear down too heavily while cutting,
and lighten up while cutting the last little bit. Use a file to dress down any burrs.
- Cut a 98" length of 1/2" copper pipe
- Solder the cap to one end (ref. 1). See: Soldering
Copper Pipe Joints for instructions if you haven't soldered
copper pipe before.
- Cut a 10" length of 3/4" copper pipe
- Solder the 3/4" sweat to 3/4" male
threaded copper adapter (ref. 6) to one end of the 3/4" pipe
(ref. 4). Soldering the adapter
in this step before cutting slots in the pipe in the next step will
alleviate possible problems caused by pipe deformation while clamping
for the cuts.
- Lengthwise slots must be cut in the top end of the
3/4" copper pipe (ref. 4). Clamp the pipe in a vise or clamp it to
a work surface with C clamps.
Use some small scrap boards to distribute the clamping force to
prevent deforming the pipe.
Using a 24-tooth hacksaw, make two 3 in. long cuts in the form of
a cross as illustrated.
- Bend two of the opposing tabs created in step 5
inward a little more than the thickness of the pipe wall to allow the
tabs to overlap each other when the hose clamps are tightened.
- With a fine tipped felt pen, mark the non-capped
end of the 1/2" antenna pipe at three points 3", 7", and 11" from the end.
Extend the marks at each point all the way around the circumference of
the pipe. Label each line: "top" (at 3"), "mid"
at (7"), and "bottom" at (11"). This will help
during the tuning procedure to indicate the limits of adjustment.
- Loosely position the two hose clamps (ref. 3) over
the 3/4" copper pipe (ref. 4). Temporarily insert the non-capped
end of the 1/2" copper pipe (ref. 2) into the 3/4" copper pipe
for a distance of at least 4" or more. Tighten the top hose clamp while watching for the tabs in
the 3/4" pipe to begin overlapping each other. If the tabs jam together and don't
overlap, try loosening the clamp and re-bending two opposing tabs a
little farther inward (repeat of step 6). Once the overlap allows you to clamp the 1/2" pipe
firmly, tighten the bottom clamp firmly. Now that the clamps have formed the tabs in the proper
position, you may loosen the clamps and remove the 1/2" pipe to
make it easier to finish assembling the antenna.
- Cut a 10". length of 1 1/2 " PVC pipe
- Cement a 1 1/2" slip to 1 1/2" female
threaded PVC adapter (ref. 14) on each end of the 10" PVC pipe
- Screw the 1 1/2" male threaded to 3/4"
female threaded galvanized iron reducing bushing (ref. 7) into the
PVC adapter at either end of the 10" PVC pipe. The threads are tapered so the
fittings will get tight when they are threaded together about half
way. Tighten firmly with a wrench
or large channel-lock pliers.
- Screw the threaded end of the adapter (ref. 6) previously
installed on the 3/4" copper pipe (ref. 4) into the 3/4"
threaded center hole in the reducing bushing (ref. 7). The threads are tapered so the
fittings will get tight when they are threaded together about half
way. Tighten firmly with a
wrench or large channel-lock pliers.
- Install the pipe grounding clamp (ref. 5)
onto the upper portion of the 3/4" sweat to 3/4" male
threaded copper adapter (ref. 6). This is called a "grounding
clamp" in the electrical trade, but is actually being used here to
make the RF connection to the copper antenna pipe.
- Fasten the completed loading coil assembly to the 1
1/2" PVC pipe section (ref. 9) oriented with the tapped end of the
coil down. Use two plastic wire
ties (ref. 8) around the loading coil pipe and the 1 1/2" PVC pipe
as illustrated. Position the
tie wraps just inside the caps as illustrated. If your wire ties aren't
long enough, you can daisy chain two or more to get the required length. Tighten the wire ties as much as you
can with pliers. Apply a dab of
PVC cement to both wire ties where they contact the 1 1/2" PVC pipe
to prevent them from slipping.
- Cut the 12" top coil end wire just long enough
to comfortably reach the "ground clamp" (ref. 5) without
straining. Scrape (if necessary) and tin the end of the wire. Insert the end of the wire into the
ground clamp and tighten the wire clamping screw firmly.
Mounting The Weatherproof Box
Since the exact mounting
position and dimensions are determined by the size and shape of your chosen
weatherproof, the following steps are written in general terms.
Here are some important
points to keep in mind.
- The transmitter should be mounted no higher than
the bottom of the loading coil winding. This will minimize capacitive
coupling between the coil and the transmitter board.
- The antenna and ground leads that run from the
transmitter to the coil and the metal pipe mast, respectively, should be
kept as short as possible for Part 15 compliance. Generally, this limits
the choice of transmitter orientation inside the box to the vertical
position with the transmitter rear panel facing up, as illustrated.
- The component side of the transmitter circuit board
must be accessible for setting the frequency switches and adjusting the
trimmer capacitor. Again, the
transmitter orientation shown in the illustration is good for accessing
- The weatherproof box should be no larger than
necessary to reduce wind resistance and stress on the box mounting
points. For a heavier box, you
might consider using two U-shaped pipe mounts to attach the box more
Now on with mounting the box:
- Drill holes in the box for the two mounting screws
(ref. 13). Exact position is not
important, but they should be spaced far apart and should be on the
vertical center line of the box.
- Drill holes in the box large enough to pass the
power and audio cable plugs into the box. These holes should be offset
horizontally from the box center line enough to clear the mast pipe and
must be positioned upward from the transmitter enclosure rear panel in
its final position. See
illustration. Note: if your
audio source is already monophonic, you need only one audio cable
plugged into either audio jack on the transmitter. If your source is stereo, you will
need both left and right audio cables.
- Drill a separate hole large enough to pass the
antenna and ground wires out of the box.
- Temporarily thread the top end of the antenna mast
pipe (ref. 12) into the threaded PVC adapter (ref. 14) and tighten
- Hold the box in its final position against the mast
pipe and mark the locations on the pipe for the two mounting screws
(ref. 13). Drill holes in the
mast pipe at the marked locations.
Use a drill sized to just clear the diameter of the screws at the
valleys of their threads. Run the screws in and out of the holes a
couple times to form the threads in the pipe sections.
- With the same drill bit used in the previous step,
drill a hole in the mast pipe for the self-threading ground screw (ref.
13) approximately as shown in the illustration. Run the screw in and out of the hole
a couple times to form the threads in the pipe.
- Attach the box to the mast pipe with two
self-threading screws (ref. 13) through the mounting holes just
- Attach the mating halves of the adhesive velcro
strips (ref. 10) to the bottom of the transmitter enclosure and to the
inside of the weatherproof box, respectively as illustrated. Remove the top cover from the
transmitter for later access to the switches and trimmer capacitor for
final tuning. You may elect to
just leave the cover off in the final installation.
- Route the antenna and ground wires from the
transmitter rear panel out through the hole in the box that you
previously drilled for them. Cut
the black ground wire to the minimum length that will comfortably reach
the ground screw on the mast pipe, allowing an extra 3/4" for the
connection. Strip 3/4" of
insulation from the wire.
Lightly twist the conductor strands together, and tin the exposed
wire with solder. Don't connect the ground wire to the mast pipe yet.
- Cut the white antenna wire to the minimum length
that will comfortably reach the uppermost tap on the coil (not the upper coil end
wire), allowing an extra 1/4" for the connection. Strip 1/4" of insulation from
the wire. Lightly twist the
conductor strands together, and tin the exposed wire with solder. Don't connect the antenna wire to the
coil yet. You will do that later
after selecting the proper tap in the tuning procedure.
- Remove the antenna assembly from the mast pipe by
unscrewing at the antenna assembly/mast pipe fitting. Lay the antenna assembly aside while
you install the mast pipe in its final location.
Installing The Mast Pipe
Install the mast pipe (ref. 12)
securely in its final position making sure that the threaded end with the
ground screw hole is at the top. How
you mount the mast pipe is up to you.
If the mast pipe is fairly short, dig a hole about 3
ft deep and 1ft in diameter. Place
the mast pipe in the hole. Mix a bag or two of concrete and pour around the
pipe in the hole. Support the pipe
vertically (check with a level) until the concrete sets.
A longer mast pipe may be installed on the side of a
building. You can use TV antenna mast wall mounts (RadioShack), or you can
fabricate wood or metal wall standoff supports and use U shaped pipe mounts
or U bolts. Wood supports can be
fabricated from 2 x 4 wood stud stock. Metal supports can be fabricated from
universal angle iron stock and bolts. The pipe should extend all the way to
ground level to provide the necessary signal ground path and added support.
Grounding The Mast Pipe
Grounding is very important
to the performance of your antenna.
The mast pipe needs to be well grounded to minimize antenna ground
loss. High resistance to ground will
cause most of your signal to be dissipated in the ground resistance. Ground resistance drops when you are able
to connect to a conductor that has a large area buried in moist ground.
A metal cold water pipe that
has a good conductive path underground can sometimes provide a very good
ground, but presence of corrosion, gaskets, poorly conducting fittings or
plastic pipe sections can severely affect the conduction path.
If your soil around the mast
is relatively rock free, you will get good results with several 8-foot long
electrical grounding rods driven vertically into the soil around the base of
the mast. You will need to connect the tops of the rods to the mast with
heavy copper wires (#14 or #12 are practical sizes). Use one or more grounding clamps above
ground level at the base of the mast pipe to connect the ground wires. The
ground rods are made of steel clad with an outer jacket of copper. They are available from home improvement stores
and electrical supply dealers.
Burying a number of bare
copper wires at least 6 ft. long (longer is better) in a radial pattern around the base of the mast is a popular
solution, especially when your soil is too rocky for ground rods. Use as many
wires as you can manage and make them as long as possible. Use un-insulated wire that is #14 gauge or
heavier. Solid un-insulated wire is
available in various size rolls from home improvement store and electrical
supply dealers. You can rent a
powered wire trencher from your local tool rental store. They cut a slot in
the ground with a bladed wheel. You
can lay a lot of wire in one day with a trencher. The wires need to be bonded
together at the mast and connected to the mast. You can use one or more grounding clamps at the base of the
mast pipe above ground level.
Mounting The Antenna And Transmitter To The
Top of the Mast Pipe
- Screw the antenna assembly onto the top of the mast
pipe and tighten firmly.
- Attach the black ground wire to the mast pipe by forming
the wire around the ground screw and then tightening the screw firmly
down on the wire to make good contact.
- Slide the 1/2" antenna pipe (ref. 2) back into
the slotted 3/4" pipe (ref. 4) for a distance of 7" so the
line labeled "mid" is even with the top of the 3/4" pipe,
and tighten the two hose clamps (ref. 3) sufficiently to keep the
antenna pipe from slipping downward.
Proper tuning of your antenna
is critical to achieving maximum performance. The antenna has a very
sharp resonance point. You must follow the tuning instructions
carefully. Tuning must be done with
the antenna installed in its permanent location.
- Route the audio and power cables up to the
transmitter, pass them through the holes in the transmitter box, and
plug them into the transmitter jacks.
- Apply power to the transmitter and connect the
audio cables to an audio source.
- Loosen the two hose clamps enough to be able to
work the 1/2" pipe up and down for adjustments, but not so loose
that it slides downward on its own.
Start at the midpoint of adjustment range, which is the point
where the 1/2" pipe is inserted into the top end of the 3/4"
pipe for a length of 7".
The range of adjustment is plus or minus 4" from the
midpoint. Never raise the
antenna to a point where less than 3' is inserted into the top of the
3/4" pipe, or it will not be supported properly by the hose clamps.
- Insert the probes from an analog or digital
voltmeter into the two holes on the right side of the transmitter
circuit board labeled T1 (positive) and T2 (negative). Set the meter to read DC volts, and
set it to the lowest range that will allow reading up to about 15 volts
DC. Your voltmeter should have
an input impedance rating of at least 10 megohms. This is common for virtually all
battery operated meters currently on the market.
- Choose your desired operating frequency in the
range between 1500 kHz and 1700 kHz.
Pick a frequency that is unused in your area. Set the 8-position DIP switch, S4, to
your chosen frequency according to the chart in the manual. Also, double check that all four
switches on the 4-position DIP switch, S5, are set to the ON position.
Set the trimmer capacitor, C5, to its minimum setting (rotate
until the half moon shaped metal plate on the top faces the front side
(control side) of the transmitter circuit board.
- Set the front panel GAIN control to its minimum
setting (fully counterclockwise) to ensure the transmitter is not being
modulated during the tuning process.
- Holding the short antenna wire lead coming from the
transmitter antenna plug, touch it to the topmost loading coil tap
(topmost tap, not the top end of the coil). Note the meter reading.
Now touch the wire to each successive tap, moving downward along
the taps (including the bottom coil end wire) until you find the tap
that gives the highest meter reading.
If you see the voltage peak and then start to drop lower as you
move to successive taps, go back to the one that gives the highest
reading. Temporarily clamp the
wire in contact with this tap using an alligator clip or small paper
clamp and move your hands and body away at least 2 feet. Note the meter reading and then move
and clamp the wire to successive taps on either side of this tap until
you find the one that gives the maximum meter reading with your hands
and body away from the antenna at least 2 feet.
- Fine tune the antenna by working the 1/2" pipe
antenna up or down about a half inch at a time until you find the
position that gives the highest meter reading with your hands and body
at least a 2 feet away from the antenna.
- If the voltage reading at the tuning peak is
greater than 13 volts DC,
increase the trimmer, C5, capacitance by rotating the trimmer
clockwise until the voltage drops to 13 volts DC. Re-adjust the antenna length downward
until the voltage peaks again.
If the voltage peak is still higher than 13 volts DC. Repeat the
process of increasing the trimmer capacitance and re-tuning the antenna
until you get 13 volts DC at the tuning peak. You should only have to repeat this process a couple of
times. This is an important
step. Don't treat it lightly. If
the voltage is not reduced to 13 volts DC, your RF output signal may be
distorted resulting in audio distortion of the received signal. When the meter reads 13 volts DC, the
antenna is perfectly matched to the transmitter: the power output will
be maximum and the audio will be undistorted.
- Solder the transmitter antenna lead to the selected
tap. All other taps above and below your selected tap will remain
unconnected. The portion of the coil between the selected tap and the
top end wire now has the required inductance to tune to your selected
frequency. The portion of the coil below your selected tap is
electrically open-circuited and does not contribute to the coil
- Re-check that the voltage reading is still 13
volts. If it has changed higher
or lower, repeat steps 8 and 9 to ensure the antenna is tuned properly
after soldering the transmitter antenna wire, and then tighten the two
hose clamps firmly.
- Adjust the GAIN, MODULATION, and COMPRESSION
controls to your preference according to the instructions in the manual.
If you choose to use an external audio processor for
level, compression and limiting control, set the GAIN and MODULATION
controls to maximum (fully clockwise) and set the COMPRESSION control to
minimum (fully counterclockwise).
Your external audio processor must then be set for the proper
audio level and limit level to achieve 100% modulation without over
Sealing The Box Against Moisture
Apply RTV silicone adhesive
or 100% silicone caulk liberally around all wires where they enter the box to
block any moisture from entering the box. .This is an important step. Any water that gets onto the circuit board
will quickly damage the board. Attach the box cover.
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