AM1 • 13
Once the tuning capacitors and some sort of antenna have been installed,
it’s time to align your transmitter.
ALIGNMENT PROCEDURES
Keep all tests very brief until you have carefully chosen an open operating
frequency in the AM broadcast band.
1. Tune an AM receiver to a quiet spot on the dial where you wish to
receive your transmitter.
2. Connect an antenna to the RF OUT jack.
3. Energize the circuit with a suitable power source.
4. Using the plastic tuning tool, adjust coil L2 until you hear the AM1’s
carrier signal. If the radio is very close and you have configured the AM1
for a mike input, you may hear a feedback squeal. It might seem a little
tricky at first to set the exact frequency you want, as the frequency may
be affected by how close your hand is to the circuit board.
5. Rotate the LEVEL ADJ control to its full clockwise position. This is the
maximum level input position. The best audio source for testing if you’ve
configured the AM1 for line level is the line level outputs of a tape deck
or CD player. Most stereo systems have a variety of output jacks of
which one or more are “line level”. Connect the audio source to the
AUDIO IN jack . Adjust R12 for undistorted audio.
EXPERIMENTAL “BROADCASTING” PROJECTS
To use the AM1 successfully as a “broadcasting” service to interested
listeners in a school or immediate neighborhood, most of your effort will be
concentrated on smoothly “managing” or mixing the audio signals into the
transmitter input. Operation of the transmitter consists of the following:
If you wish to “mix” between audio inputs, i.e. microphone and music
sources, you may need an external audio “mixer” unit. Many sources exist
for audio mixers, including the Radio Shack No. 32 - 1105 which is one of
least expensive that we have found. There are more sophisticated models,
but bear in mind that model numbers and specs for such units can change
from year to year. Also, some home entertainment audio equipment includes
simple mixing capabilities which will permit you to fade and “cue” music and
microphone inputs.
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