User manual

FM100B • 5
ADJUSTING YOUR FM100B TRANSMITTER:
Keep all tests very brief until you have carefully chosen an open operating
frequency in the FM broadcast band.
1. Transmitting Frequency:
After finding a suitable "open" frequency in the 88-108 MHz FM band, adjust
the frequency by first getting the FM100B into setup mode by pressing both
FREQ keys at the same time. Then use FREQ UP and FREQ DOWN keys
until you hear the carrier frequency on a nearby FM radio. No audio input is
needed to make this first adjustment, you can simply listen for a "quieting" in
the normal background noise "hiss."
The modulation sensitivity of your FM100B will vary from one end of the
broadcast band to the other, but not enough to worry about. This is explained
by the characteristic curve of the varactor diode. In order to maintain the
proper 75 KHz deviation, your front panel level control should be set so that
the audio level meters read 0 with an occasional blink or two over that on the
meter. The clipper circuit internal to the BH1415 will prevent over-modulation.
2. Audio Connection:
Hooking up an audio source to your FM100B is really quite simple. However,
there are some general rules:
• A terribly distorted sound is a sign of too much audio level. Simply
rotate the level potentiometers (R42 and R72) CCW to reduce the
level. Make sure you rotate each one about the same amount to
maintain proper stereo balance.
• Stereo LP turntables are low-level output and will require the use of a
preamplifier for proper audio input to the FM100B.
• NEVER connect the FM100B audio inputs to speaker outputs of a high
power stereo system; such a connection will destroy the IC chips.
3. Stereo balance:
Due to the precise characteristics of the BH1415, we no longer need to adjust
this. I left this here for the benefit of those boys (and girls) that are die-hard
FM100 fans.