Lectrosonics Inc LMAM 사용자 설명서

Servo Input

The LMA input is a radically different input system com-

pared to previous Lectrosonics transmitter microphone 

inputs. It is so superior that this input system will eventu-

ally be utilized by all Lectrosonics UHF transmitters. The 

improvements are audible and make the transmitters 

easier to use and much harder to overload. It is no 

longer necessary on some mics to introduce pads to 

prevent overload of the input stage, divide the bias 

voltage down for some low voltage mics, or reduce the 

limiter range at minimum gain settings.

Input Limiter

The transmitter employs a digitally-controlled analog 

audio limiter prior to the analog-to-digital converter.  

The limiter has a range greater than 30 dB for excellent 

overload protection.  A dual release envelope makes 

the limiter acoustically transparent while maintaining 

low distortion.  It can be thought of as two limiters in 

series, connected as a fast attack and release limiter 

followed by a slow attack and release limiter.  The limiter 

recovers quickly from brief transients, so that its action 

is hidden from the listener, but recovers slowly from 

sustained high levels, to both keep audio distortion low 

and preserve short term dynamic changes.

No Pre-Emphasis/De-Emphasis

Because the signal to noise ratio of the hybrid system is 

so high, there is no need for conventional pre-emphasis 

(HF boost) in the transmitter and de-emphasis (HF roll 

off) in the receiver.  Thus, the possible distortion prob-

lems associated with pre-emphasis and de-emphasis 

are eliminated.

Pilot Tone Squelch

The hybrid system uses one of 256 different ultrasonic 

tones between 25 and 32 kHz, that modulate the carrier 

to operate the receiver squelch.  The pilot tone frequen-

cy is chosen according to which of the 256 channels 

has been selected by the frequency switch setting. The 

benefit of a pilot tone squelch system is that the receiv-

er 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 400 Series 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.

Antenna

The antenna consists of a permanently attached flex-

ible, unbreakable 1/4 wavelength galvanized steel cable.

Freq

Switches

Bicolor

Modulation

LEDs

9V

Battery

Bicolor
Power
LED

LMa Block Diagram