Lectrosonics UM700 User Manual download pdf (Page 5)

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 micro-

phone.

Rio Rancho, NM – USA

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Lectrosonics UM700 User Manual Page 5

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