Lectrosonics UM700 User Manual
UM700
ENCRYPTED DIGITAL
UHF BELT-PACK TRANSMITTER
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
Rio Rancho, NM
www.lectrosonics.com
UM700
TABLE OF CONTENTS
INTRODUCTION ................................................................................................... 3
GENERAL TECHNICAL DESCRIPTION ............................................................. 4
CONTROLS AND FUNCTIONS ........................................................................... 6
BATTERY INSTALLATION .................................................................................... 8
OPERATING INSTRUCTIONS ............................................................................. 9
OPERATING NOTES ............................................................................................. 9
ADJUSTING THE TRANSMITTER FREQUENCY .............................................. 9
MICROPHONE CORD TERMINATION .............................................................. 10
5-PIN INPUT JACK WIRING .............................................................................. 11
TROUBLESHOOTING......................................................................................... 13
SPECIFICATIONS AND FEATURES ................................................................. 14
SERVICE AND REPAIR ...................................................................................... 15
RETURNING UNITS FOR REPAIR .................................................................... 15
WARRANTY ........................................................................................... Back cover
The UM700 transmitter is FCC type accepted under Part 74: 470-608MHz and 614-802MHz
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LECTROSONICS, INC.
Digital Frequency Agile UHF Belt-Pack Transmitter
INTRODUCTION
The 700 Series wireless system provides a combination of outstanding audio quality
and secure encryption. This unique combination makes the 700 Series equally
suitable for high-end studio and stage applications, and for corporate and government applications where security is a concern.
Several advantages are provided by a digital wireless system:
• A digital radio system provides outstanding signal to noise ratio.
• The signal to noise ratio of a digital radio system stays constant all the way out to
the end of the usable range of RF signal strength.
• A DSP controlled analog limiter provides superior level control.
• Eavesdropping is extremely difficult due to the secure encryption.
The UM700 is a durable, machined aluminum package in a belt-pack configuration
with a removable, spring loaded belt clip. A 5-pin input jack provides taps for any
microphone or line level signal. The unit is powered by a single 9 Volt alkaline or
lithium battery, or from external DC using an optional battery eliminator. The
antenna is a detachable, locking 1/4 wavelength flexible bronze alloy cable that
connects to a 50 Ohm SMA port on the control panel.
Only the UM700 transmitter is covered in this manual. Companion receivers are
covered in separate manuals. The UM700 will operate with any 700 Series
Lectrosonics receiver in the same frequency block.
Rio Rancho, NM – USA
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UM700
GENERAL TECHNICAL DESCRIPTION
GENERAL
The 700 series encrypted digital wireless microphones use an all-digital communications link for excellent sound
quality and data security.
In the transmitter, the audio first passes through a DSP-controlled dual envelope analog limiter. The signal is then
digitized and fed to a DSP (digital signal processor). The DSP uses a proprietary audio encoding scheme to lower
the bit rate and provide the high entropy required for secure encryption. The bit stream is then encrypted, apportioned into packets, and sent over the air using a proprietary digital modulation scheme.
In the receiver, the digital baseband signal is demodulated to recover the original bit clock and data stream. The
DSP separates out the packet headers and decrypts the audio data. The audio data is then decoded to recover the
original audio signal.
Mic
Jack
1
2
3
4
5
+3.3V Bias
Supply
Encryption
Key Link
Bicolor
Modulation
LEDs
<--See 5-Pin Input Jack Wiring for details.
Hi/Lo
Pass
Filter
Phase
Locked
Loop
Input
Amp
LF
Rolloff
Shunt
Limiter
Freq
Switches
Audio
Audio
Level
Microprocessor
Voltage
Controlled
Oscillator
A-D
Converter
11001001
Dual
Envelope
Limiter
Digital Signal Processor
Encode
Digital
Modulator
Encrypt
Battery
RF
Amp
9V
Switching
Power
Supply
Isolator
50
Bicolor
Power
LED
+3.3v
+1.8v
+9v
-3v
DSP-CONTROLLED DUAL ENVELOPE ANALOG LIMITER
In order to make the very best use of the high quality A/D converter, microphone audio is limited in the analog
domain first before being sampled. The DSP controls this process, but because the limiting is done in analog, levels
near the converter’s maximum may be used without fear of clipping.
The limiter has a fast attack, but different release characteristics, depending on the nature of the signal that drove
the input into limiting. Brief transients result in a fast decay, to avoid “pumping” effects, while sustained loud signals
result in a slower decay, to keep distortion to a minimum. The result is a transparent-sounding limiter with excellent
low distortion characteristics.
DIGITAL SIGNAL PROCESSING AND MODULATION
The preamplified and limited audio signal is converted to digital using a 24-bit A/D converter and fed to the DSP.
Within the DSP, the audio is encoded to reduce the bit rate and increase entropy in the data stream prior to encryption. The data stream is then encrypted and apportioned into packets, delimited by packet headers. The complete
bit stream is modulated onto the carrier using a modified pi/4 DQPSK (differential quadrature phase shift keying)
method. This modulation method makes efficient use of the RF spectrum and is easy to demodulate reliably.
RF OUTPUT SECTION
Intermodulation (IM) occurs in the final amplifier stages of conventional transmitters when the transmitters are within
a few feet of each other. This can create serious problems in multichannel wireless systems when an IM signal falls
on the carriers, IF frequencies, local oscillator and image frequencies of the systems being operated. To eliminate
this problem in the UM700, the modulated radio signal passes through a circular isolator before entering the an-
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LECTROSONICS, INC.
Digital Frequency Agile UHF Belt-Pack Transmitter
tenna. The circular isolator functions like a “one-way check valve” to allow the RF signal to pass through to the
antenna, but not to pass backwards into the amplifier stage. RF signals from other nearby transmitters cannot reach
the output amplifier in the UM700. This provides excellent stability and eliminates IM in the output stage of the
transmitter.
LONG BATTERY LIFE
High efficiency circuits and switching power supplies 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
700 Series wireless systems are available on eight different “blocks” of 256 frequencies, from 537.600 to 767.900
MHz. Each of these blocks provides 256 selectable frequencies in 100 kHz steps over a 25.6 MHz bandwidth. This
wide variety of selectable frequencies alleviates carrier interference problems in mobile or traveling applications. Two
16-position rotary switches on the side panel of the unit are used to select the frequency.
The UM700 transmitter section uses a synthesized, frequency selectable main oscillator The frequency is extremely
stable over a wide temperature range and over time.
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 UM700 consists of a flexible 1/4
wavelength bronze cable, detachable via an SMA connector. The impedance of this connector is 50 Ohms.
ENCRYPTION SYSTEM
The 700 Series employs state-of-the-art 128-bit encryption for exceptional data security. (128-bit encryption means
there are 300 trillion, trillion, *trillion* possible keys, assigned with equal probability.) The system offers three levels
of security, trading off ease of use for immunity to attack.
LEVEL 1 offers the most intuitive operation. Once the key has been set, the equipment may be operated exactly the
same as a traditional analog system. The transmitter and receiver may be powered on in any sequence, and the
transmitter may move in and out of range without consequence (except normal squelching). Security in this mode is
excellent, but the scrambling sequence repeats approximately every 20,000 bits, theoretically exposing the user to
differential attacks. Due to its ease of use and quite effective security, level 1 is the default security level.
LEVEL 2 offers much greater encryption strength, at the cost of slightly less intuitive operation. In level 2, the
scrambling sequence never repeats (i.e. the PRNG is free-running), so the receiver must be on and ready to receive
when the transmitter is first switched on. Some signal loss is tolerated but if the transmitter should wander out of
range for more than ten seconds, it will be necessary to switch it off and on again to restart the sequence,
resynchronizing with the receiver. Security in this mode is a great deal stronger than level 1, since the scrambling
sequence never repeats. Only if the sequence is deliberately reused (i.e. by cycling transmitter power after prolonged
signal loss, or by reusing the same key session after session) is a differential attack possible even in theory.
LEVEL 3 offers the strongest encryption of all, again at the cost of some convenience. Level 3 is much like level 2,
except that the equipment itself enforces a policy that NO PORTION OF ANY SCRAMBLING SEQUENCE SHALL
EVER BE USED MORE THAN ONCE. This is a fundamental tenet of cryptography: key reuse leads to vulnerability.
Thus, level 3 security is about as close to the holy grail of the one-time pad as any wireless vendor is likely to offer at
a reasonable price. Operation is a little different in level 3:
• The transmitter starts sending immediately after receiving a key ONLY. It does not send when first powered on.
• Only one transmitter may receive each key.
• If the transmitter is out of range of the receiver for more than ten seconds, it will be necessary to generate a
new key in order to continue using the system.
All three levels offer strong encryption, so each user may make a policy decision based on an assessment of risk.
Those requiring ease of use may relax, knowing that eavesdropping is extremely difficult even in level 1. Many users
may find level 2 to be just as convenient, allowing them to use greater encryption strength. Those users willing to
follow stricter security procedures can use level 3, the strongest encryption available today from a wireless microphone.
Rio Rancho, NM – USA
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