Lectrosonics UM100 - Manual (Page 5)

Multi-frequency UHF Belt-Pack Transmitter
PRE-EMPHASIS/DE-EMPHASIS
The signal to noise ratio of the 100 system is extended by using pre-emphasis (HF boost) in the transmitter and de-
emphasis (HF roll off) in the receiver. Pre-emphasis and de-emphasis in an FM radio system usually provides about
a 10 dB improvement in the signal to noise ratio of the system, but the high frequency boost in the transmitter must
be removed in a purely complimentary manner or else the frequency response of the original audio signal will be
altered. The dual-band compandor in the 100 system essentially provides a dynamic pre-emphasis/de-emphasis
function with low distortion.
LONG BATTERY LIFE
High efficiency circuits throughout the design allow over 4.5 hours of operation using a single 9 Volt alkaline battery.
(A 9V lithium battery will provide over 14 hours of operation.) The battery compartment is a unique mechanical
design which automatically adjusts to fit any brand of battery. The battery contacts are spring loaded to prevent
“rattle” as the unit is handled.
FREQUENCY AGILITY
The transmitter section uses a synthesized, frequency selectable main oscillator The frequency is extremely stable
over a wide temperature range and over time.
Two rotary switches, located on the side panel of the unit, provide 256 frequencies in 100kHz steps over a 25.5MHz
range. This alleviates carrier interference problems in mobile or travelling applications.
ANTENNA
At UHF frequencies, where wavelengths and antennas are shorter than at VHF frequencies, a resonant length wire is
preferred over using the microphone cable as the antenna. The antenna on the UM100 consists of a flexible 1/4
wavelength bronze cable.
Rio Rancho, NM – USA 5