Oscillator Section
The Oscillator section was built on a small piece of PC
board measuring about 2 and 1/4 inches square. The layout is
a little cramped but can be done easily using "manhattan
style" construction with almost any reasonablly sized parts.
I usually start in the middle with the transistor and then work
out from there. The two LED's are used as Varractor diodes and
work very well in this application. The Crystal has already been
sealed up in Hot Melt Glue with it's 100 ohm Heater resistors
on the sides of the crystal and it's 2N2222 transistor sensor
which was superglued to it's side to make construction easier.
Then the oscillator board is mounted on the base plate board
which is 6 and 1/4 inches square with a 2 and 2/8 inch front
panel soldered to the base. I put a piece of foam board underneath
the oscillator and then grounded it to the base with brass shim
stock strips. then build the foam board sides and top to insulate
the whole oscillator section from any changes in temperature. |
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Buffer/ PA Section
The Buffer Amplifier and Power Amplifier
module was built on a 1 and 3/4 inch by 5 and 1/4 inch pice of
PC board. It's position in the MEPT transmiter is along the left
side of the base PC board looking from the back. It's layout
is about the same as the flow of the RF from the oscillator input
to the antenna output. I laid it out so it looks very similular
to the schematic to help make it easy to build and to troubleshoot
if something goes wrong. Manhattan style building is very handy
for this type of construction as you can make the built circuit
look very similar to the drawn schematic. If you make a mistake
or want to make a component change, it is easy to follow on the
schematic.
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Crystal Heater Section
The Crystal Heater controller section is built on a 2 and 3/4
by 1 and 7/8 inch piece of PC board. I laid this one out about
the same as I did the Oscillator section. I positioned the 741
OpAmp in about the center and built the rest of the circuit around
it. I did think about putting the two indicator LED's on the
front panel and may move them later but for now with the open
base, I can peek in and see that they are lit. I did use a socket
for the 741 OpAmp. This could be compressed more but I had the
room so this is how it turned out. I used the Model 2 Crystal
Heater from M0AYF. The crystal heater schematic came from HERE |
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Keyer and Power conditioning
circuit
The Keyer and Power conditioning
circuit board measures 3 and 3/8 by 1 and 1/4 inchs and is the
catch all for all the other stuff including the K1EL keyer chip
and it's switching, a data inverter transistor to get the keying
so that when the CW is key down it shifts the carrier up. A 5
volt regulator and some extra electrolytics to keep the +12 VDC
stable. Also the wiring for the ON/OFF switch and the way I keep
power to the crystal heater when the transmitter is off.
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The module schematics are found HERE
in .PDF format so that they will be easy to print out. My skills
using the schematic drawing programs are a bit lacking but I
am working on it. Someday, I will be able to provide fancy SPICE
type drawings for my projects, but for now the paper and template
are still easiest for me. |
BACK PANEL
2 and 3/8 by 6 and 1/4 inches with
BNC RF connector and a Phono plug for power installed.
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Front Panel
Size 2 and 3/8 by 6 and 1/4 inches with the power
LED and switch on left side and pot for fine frequency control
on the right. This board along with the back panel is just soldered
along the bottom to the base plate PC board. Then the Oscillator
is installed. Then the back panel and then the rest of the modules
are put on the base plate as they are completed. I use strips
of brass shim stock to provide a good low inductance connection
to the base plate by attaching the modules in at least two places
to the base PC board. If you need to make a change later on,
Just remove the module and make your changes and then put it
back. Makes it real easy for projects like this one. |
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Here is the finished MEPT transmitter. It really is
easier to complete in modules as you can work on one module at
a time to make construction easier. When all of the modules are
completed then you can combine them to make a completed unit.
It seems to break up the construction into managable steps and
also allows you to check out each module as you complete it.
It starts with doing the Oscillator first, then the Heater Control
unit, then the buffer/amplifer, and last the keyer and power
wiring. |
Here is the constructor of the first Model 2 MEPT transmitter.
This is my buddy Perry KC7VHS. You will see his call around the
world from his home brewed MEPT transmitter. He is operating
it on a Butternut HF-6V with twenty 22 foot radials mounted in
his back yard . I think he really enjoyed building it and did
a really good job. The module pictures are from his transmitter.
This was his first BIG building project and is proof that if
you take your time, You to can build a nice stable MEPT transmitter
in about a week's time. |
Here is the construction of the second Model 2 MEPT transmitter.
This my friend Robert KE5OFK. You will soon see his call on the
30 meter band. His transmitter is set for 250mW and a CWFSK speed
of 3 second dits. He will probably change to 6 second dits as
soon as he gets a few contacts under his belt. This is the first
homebrew transmitter project he has ever done. But now it is
tested and working and ready to be hooked to the antenna. His
antenna is going to be a Gap Titian Vertical on 20 meters. He
would appreciate any reports of his signal being received.
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