How it Works
Lectrosonics
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UM200
User Manual
14 pgs252.7 Kb0

Lectrosonics UM200 User Manual

UM200
FREQUENCY-AGILE, BELT-PACK
TRANSMITTER
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
Rio Rancho, NM
INTRODUCTION
The design of the UM200 was the direct result of numerous conversations with users, staging and touring companies and dealers across the US. The specific concerns and needs brought up in these conversations led directly to the development of the operational features offered on the UM200. Two hundred fifty six frequencies are user selectable in 100kHz steps to alleviate interference problems in travelling venues, and the low frequency roll­off is user adjustable to adapt to varying acoustic environments and preferences.
The UM200 is a rugged, machined aluminum package with a removable, spring loaded belt clip. The input section provides a correct input tap for virtually any microphone or line level audio source. 5 Volts of bias voltage is available to power electret mics with either positive or negative bias. Level indicating LEDs are provided on the control panel to make level settings quick and accurate, without having to view the receiver. The battery compartment accepts any 9 Volt alkaline battery and makes a positive connection via self-adjusting contacts. The antenna is a detachable, locking 1/4 wavelength flexible wire that connects to a 50 Ohm port on the transmitter.
Only the UM200 transmitter is covered in this manual. Companion receivers are covered in separate manuals. The UM200 will operate with any 200 Series Lectrosonics receiver in the same frequency group.
TABLE OF CONTENTS
INTRODUCTION .......................................... 3
GENERAL TECHNICAL DESCRIPTION .......................... 4
CONTROLS AND FUNCTIONS ................................ 6
BATTERY INSTALLATION ................................... 8
OPERATING INSTRUCTIONS ................................. 8
OPERATING NOTES ....................................... 9
ADJUSTING THE TRANSMITTER FREQUENCY ................... 9
UM200 INPUT JACK WIRING ................................. 10
TROUBLESHOOTING ....................................... 11
SPECIFICATIONS AND FEATURES ............................ 12
SERVICE AND REPAIR ..................................... 13
RETURNING UNITS FOR REPAIR ............................. 13
WARRANTY ........................................ Back cover
The UM200 transmitter is FCC type accepted under Part 74: 470-608MHz and 614-802MHz
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GENERAL TECHNICAL DESCRIPTION
The UM200 transmitters are comprised of a number of functional sub-systems as shown in the block diagram below.
GENERAL
The 200 system uses 75kHz wide deviation for an extremely high signal to noise ratio. The transmitter circuits are all regulated to allow full output power from the beginning (9 Volts) to the end (6 Volts) of battery life. The input amplifier uses a Motorola 33178 op amp for ultra low noise operation. It is gain controlled with a wide range input compressor which cleanly limits input signal peaks over 30dB above full modulation.
DUAL BAND COMPANDOR
Traditionally, compandors have been a source of distortion in wireless microphone systems. The basic problem with conventional systems is that the attack and decay times are always a compromise. If the time constants are fast, high frequency transients will not be distorted, but this will cause low frequency distortion. If the time constants are slower, low frequency audio distortion will be low, but high frequency transients will then be distorted. The 200 system introduces an entirely new approach to solving this basic problem, called "dual-band companding."
There are actually two separate compandors in the 200 system, one for high frequencies and one for low frequencies. A crossover network separates the frequency bands at 1kHz with a 6dB per octave slope, followed by separate high and low frequency compandors. The attack and release times in the high frequency compandor are fast enough to keep high frequency transient distortion at a low level, and the low frequency compandor uses slower time constants, reducing low frequency distortion to well below that of a conventional compandor.
+5V BIAS
SUPPLY
SHUNT
LIMITER
LF ROLL-OFF
INPUT AMP
LIMIT
LED
SET LED
AUDIO LEVEL
PEAK AUDIO
INDICATOR &
LIMITER DRIVER
LP
FILTER
Vref
TREBLE
COMPANDOR
BASS
LP FILTER
HP FILTER
Vreg
Vreg
PILOT TONE
OSC
+5VDC
+3.6VDC
COMPANDED AUDIO
TO XMTR
MUTE
PWR
+9VDC
PWR
LED
1 2 3 4 5
MIC
JACK
PHASE LOCKED LOOP
DIVIDER
FREQ
SWITCHES
PRESCALER
LOW PASS
FILTER
COMPANDED
AUDIO
Figure 1 - UM200 Block Diagram
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VOLTAGE
CONTROLLED
OSCILLATOR
TRANSMITTER
NO PRE-EMPHASIS/DE-EMPHASIS
The signal to noise ratio of the 200 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 noticeable 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 200 system. The dual-band compandor in the 200 Series system essentially provides a dynamic pre-emphasis/de-emphasis function with extremely low distortion.
PILOT TONE SQUELCH
The 200 system utilizes an ultrasonic tone modulation of the carrier to operate the receiver squelch. This "pilot tone" consists of a 32kHz signal mixed with the audio signal following the microphone preamp, just after the compandor, to control the audio output muting of the receiver. The pilot tone is filtered out of the audio signal immediately after the detector in the receiver so that it does not influence the compandor or various gain stages. 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. This is extremely important in applications such as with an automatic microphone mixer.
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
High efficiency circuits throughout the design allow over 4.5 hours of operation using a single 9 Volt alkaline battery. The battery compartment is a unique mechanical design which automatically adjusts to fit any brand of alkaline 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 VHF, a resonant length wire is preferred over using the microphone cable as the antenna. The antenna on the UM200 consists of a flexible 1/4 wavelength wire, detachable via a twist lock connector. The impedance of this connector is 50 Ohms at UHF frequencies.
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