User Manual
5
Rio Rancho, NM - USA
Digital-hybrid, Frequency Agile Handheld Transmitter
NO PRE-EMPHASIS/DE-EMPHASIS
The signal to noise ratio of the 400 system is high enough to preclude the need for conventional 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 10dB improvement in the signal to noise ratio of the system, but the high frequency
boost in the transmitter must be removed in a purely complementary manner or else the frequency response of the
original audio signal will be altered.
Pre-emphasis can also cause distortion in the receiver. As this signal is passed through the IF filters in the receiver,
distortion can be produced, most noticeably at full modulation. De-emphasis cannot be applied until the signal is
converted into audio, so there is no way around this problem short of eliminating pre-emphasis altogether. Neither of
these problems occur in the 400 system
PILOT TONE SQUELCH
The 400 system utilizes one of 256 different ultrasonic tones between 25 and 32 kHz, that modulate the carrier to
operate the receiver squelch. The pilot tone frequency is chosen according to which of the 256 channels has been
selected by the frequency switch setting. The basic benefit of the pilot tone squelch system is that the receiver will
remain muted until it receives the pilot tone from the matching transmitter, even if a strong RF signal is present on the
carrier frequency of the system. The UM400 extends this concept even further by insuring that all transmitters in a
system have different pilot tone frequencies so that even spurious RF from the wrong transmitters can’t open the
receiver squelch.
WIDE-BAND DEVIATION
±75kHz deviation improves the capture ratio, signal to noise ratio and AM rejection of a wireless system dramatically,
compared to the more commonly used ±15kHz deviation.
LONG BATTERY LIFE
Switching power supplies throughout the design allow over 5 hours of operation using a single 9 Volt alkaline battery. (A
9V lithium battery will provide over 14 hours of operation.) 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 under the battery door, provide 256 frequencies in 100kHz steps over a 25.5MHz range.
This alleviates carrier interference problems in mobile or traveling applications.
ANTENNA
The high output antenna utilizes the lower half of the printed circuit boards as one radiating element, with the upper half
of the PC boards and the mic capsule as the other half of the dipole configuration. This allows the mic to be held in any
position, since the user’s hands have little or no effect on the radiated power.
MICROPHONE ELEMENT
The UT400 includes the Lectrosonics VariMic mic element. The VariMic is an cardioid condenser back electret micro-
phone that is adapted for the unique circumstances of wireless microphones. The problems it solves are dynamic
range, handling noise and low frequency noise (rumble or wind).
In the VariMic, an unusual pumped source FET circuit increases the usable dynamic range 12dB and greatly reduces
distortion, just as if the FET were being supplied with 48 Volts. In addition, a unique 16 position sensitivity control at the
element itself can adjust the sensitivity in 15 steps over a 15 dB range. This is in addition to the normal gain control in
the wireless microphone. The result is the widest dynamic range of any condenser mic in a wireless microphone.
The VariMic has a three point damped rubber suspension to reduce high frequency handling noise and a generous sized
windscreen to keep wind noise and breath pops away from the microphone.