Handbook for Sound Engineers

Interpretation and Tour Group Systems 1539

Tour group systems are excellent for factory tours,
museums, outdoor events, wireless microphone applica-
tions, classroom or training, or personal use. Anywhere
you need to amplify sound but don’t have (or want) an
installed sound system.

41.4.1. FM Transmitter

A typical portable FM transmitter is shown in Fig.
41-11. The specifications for this transmitter are:

General

• Number of channels: 19 wide-band, 38 narrow-band.


• Channel tuning capable of being locked.


• SNR: 70 dB or greater.


• Output power: adjustable to quarter, half, or full.


• Audio frequency response: 50 Hz–15 kHz ±3 dB.


• Includes: a microphone sensitivity switch.


• Includes: a mute switch.


• Operates on two AA batteries.


• Includes: an LCD display that indicates battery level,
  channel, channel lock, low battery, battery charging,
  programming, and RF signal strength.


• Includes: automatic battery charging circuitry for
  recharging NiMH batteries.

Radio Frequency

• RF frequency range: 216.0125–216.9875 MHz.


• Frequency accuracy: ±0.005% stability from 32to
  122 qF.


• Transmitter stability: 50 PPM


• Transmitter range: 0 to 150 ft (45.7 m).


• Output power: less than 100 mW (216 MHz).


• Antenna: the microphone cable.


• Compliance: FCC Part 15, Industry Canada.

Audio

• System frequency response: 50 Hz–10 kHz ±3 dB
  216 MHz.


• SNR: SQ enabled; 80 dB; SQ disabled 60 dB.


• System distortion: <2% harmonic distortion (THD) at
  80% deviation.


• Microphone input: unbalanced, +4 dBu maximum,
  10 dB nominal input level adjustable, impedance
  10 k:).


• Microphone sensitivity: three position switch: high,
  middle, and low in 6 dB increments.


• Line input: unbalanced, 10 dBu nominal input level,
  3 dBu maximum, impedance 10 k:.


• Microphone power: 3 Vdc bias.

Controls

• User controls: power, mute, channel up/down.


• Setup controls: in the battery compartment, micro-
  phone sensitivity, NiMH/alkaline battery, SQ
  enable/disable.


• Programming: channel lockout, channel lock.

Indicators

• LED red: illuminated when unit is on, flashes when
  batteries are low, or to indicate charging. Flashes two
  times when muted.


• Display: channel designation, lock status, signal
  strength indication, battery life, RF power.

Power

• Battery type: 2 AA batteries, Alkaline or NiMH.


• Battery life: alkaline –10 h, NiMH rechargeable.


• Battery charging: (NiMH only), fully automatic, 13 h.


• Power supply compliance: RoHS, WEEE, UL, PSE,
  CE, CUL, TUV, CB compliant.

Physical

• Dimensions: (H × W × D) 5.0 inches × 3.0 inches ×
  1.0 in (13.0 cm × 7.6 cm × 2.5 cm).


• Color: dark gray with white silk screening.


• Unit weight: 3.9 oz (111 g).


• Unit weight with batteries: 5.8 oz (164 g).

Environmental

• Temperature—operation: 14to 104qF.


• Temperature—storage: 4 to 122qF.


• Humidity: 0 to 95% relative humidity, noncondensing.

Figure 41-11. Typical high-quality FM transmitter, the Listen

LT-700-863. Courtesy Listen Technologies Corporation.