Build the Michigan Mity Mite
for 40 meters
I wish to use this 7 element LPF design for this 40m Michigan Mity Mite
Parts needed for this 40m LPF
L1/L3= T37-6_21 turns
Let's wind theTank coil
Use a 1.25 diameter form and 20-22AWG enameled (magnet) wire.
Since I wish for this to work on 40m I need 21 turns tapped at 7 turns.
With a secondary of 4 turns. To make the tap make a loop about 1" long. Twist it a few turns
then finish the winding. Tin the loop , this is the tap
After winding L1 wrap it with a thin layer of masking tape
Wind L2 on top in the same direction. Secure L2 with a
layer of masking tape. Then tin the remaing leads.
I then mixed some 5 minute epoxy and coated the coil
I use epoxy to freeze the coil and prevent it from shifting.
Now to incorperate the 7element LPF into the Michigan Mity Mite.
Wind the needed inductors L1, L2 and L3
L1/L3 require 21 turns on a T37-2 core. L2 requires 24 turns on a T37-2 core
Prep a sheet of sustrate and install a BNC connector
The copper substrate was scrubbed with a sanding block
Then cleaned with nail polish remover to remove any dust and oils
Using pads from QRPmeand super glue gel
I'll build the 7 element LPF using the Manhattan Construction technique
Two pads start it off. Mind the spacing.
Now set L3 on the two pads
Also hook in the BNC at this time, later might be difficult
Set the next pad you can now add L2.
Add capacitor C4 (270pf)
Now add capacitor C3 (680pf)
Now add another pad and inductor L1
All the inductors are now added
Add capacitor C2 (680pf)
Finally add capacitor C1 (270pf).
This completes the 7 element LPF
Different views of the 7 element LPF (low pass filter).
Now to add the Tank coil to the substrate
I got carried away and forgot pictures
wiried in the variable capacitor and a 7.058mhz crystal
here is a better view
The instruction called for a 2N2222 transistor, I didn't have one.
So used a 2N3904 which is very close. It also said to use a heat sink.
Again did not have one. Instructions said use an alligator clip.
I manage to rework an alligator clip to fit the TO-92 case.
Using some thermal compond and a small piece of shrink tubing.
fitted the clip on the TO-92 case. A vane can be added if needed in the clip.
A NO (normaly open) red push button is used as a Key.
Actual construction is finished on this Michigan Mity Mite.
All that remains is adding power and checking it out.
Full views of 40m TX
With 12vdc applied and transmitting into a dummy load.
output on the Dummy load using a DMM was +4VDC about 400mW+/-
A weak signal wasalso heard in a SWL receiver so that means it
it is working. It could probably be tweaked for more output
with the correct transistor.