Radio Alpha Products Inc. ® Alpha 99
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microphone or key cable, or other unshielded station patch cables.
4) Poor station RF ground.
Low frequency audio hum on transmitted signal.
1) Defective microphone cord (especially, broken ground lead).
2) Dynamic (magnetic) microphone located within about two feet of 99 power
transformer. All dynamic microphones pick up some magnetically-coupled hum from
the external field of nearby power transformers. In cases where objectionable hum is
experienced while using the 99 and popular microphones such as the Heil series, the
problem usually can be resolved by keeping the microphone at least 18 to 24 inches
from the front of the amplifier and ensuring that transceiver mike gain, speech
processing, and internal drive (ALC) levels are not adjusted to exceed 10 dB. In rare
cases it may be necessary to use a ceramic or condenser type microphone.
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