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Position and solder T1 primary and secondary windings elevated from the surface of the board
as shown. The spacing between the coils should be approx. 1/8" (3mm) This will allow for
spreading or adjustment between the two, during the setup procedure. You can thread in the
screw to align the two coils, if you find it necessary
This completes the assembly
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Next, power up the receiver with a 9V battery. Turn on and the LED should illuminate. Check for
9V on pin #6 of the U1 socket. If all is ok, install the LM386 into the socket noting the position of
pin 1 shown in the graphic below.
When inserting IC, the pins are flared so that they can be retained by automatic insertion tools. Gently
rock it on a flat surface so the pins are parallel and it will insert into the socket more easily.
Alignment and Setup:
There are three ways to align your K8TND VHF Regenerative Receiver for the AM aircraft band.
The "spacing between coils" should be approx.1/8" (3mm). The further the spacing (to a limit), the more
selective the receiver will be.
1. If you have an Elmer or friend that has a signal generator, you can set it for 123 Mhz., which is the
center frequency of the AM aircraft band. Then adjust the larger coil near the antenna connector by
slightly spreading it open or closed to make the radio pick up the signal generator near midpoint on the
tuning control.
2. If you don't have access to a signal generator, you can also adjust the larger coil by stretching it
open or squeezing it closed until you get the lower, most counter-clockwise point on your tuning control
to just barely pick up the highest frequency FM broadcast station. This should give you a tuning range
that covers most of the aircraft band.
3. An easy, but not so accurate method, is to adjust the larger coil until you center the most active
channels in the middle of the tuning control range. Traditionally, most of the activity on the air band
tends to be near the center of that allocated spectrum.
If you need more audio gain, change R4 to a lower value, but not less than 15K.
Page 5 of 7
airband_111719.pdf
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