Digital Hand Held Transmitter
Rio Rancho, NM
3
General Technical Description
Introduction
The transmitter benefits from a fourth generation
design with specially developed, high efficiency digital
circuitry for extended operating time on two AA batter-
ies. The transmitter can tune across the UHF television
band from 470.100 to 607.950 MHz, with a selectable
output power of 25 or 50 mW. The pure digital architec-
ture enables AES 256-CTR encryption for applications
that require high level security.
Input Gain Range and Limiter
45 dB range of input gain adjustment allows gain
settings to accurately match the user’s voice and the
varying sensitivity of different microphone capsules. A
DSP-controlled analog audio limiter is employed be-
fore the A-D converter. The limiter has a range of more
than 30 dB for excellent overload protection. A dual re-
lease envelope makes the limiter acoustically transpar-
ent while maintaining low distortion. It can be thought
of as two limiters in series, a fast attack and release
limiter followed by a slow attack and release limiter.
The limiter recovers quickly from brief transients, with
no audible side effects, and also recovers slowly from
sustained high levels to keep audio distortion low while
preserving short term dynamics.
Frequency Selection
Operating frequency is normally selected using a
receiver or analyzer to assess signals in the local en-
vironment to avoid interference. Once an interference-
free frequency is identified, the transmitter frequency is
set to match the receiver.
The LCD on the transmitter displays frequency in MHz
and with a two character hex code that is used on
most Lectrosonics receivers.
Antenna
A unique helical antenna allows the transmitter to be
held in any position, since the user’s hands have little
or no effect on the RF output power.
Microphone Capsules
The transmitter is available from Lectrosonics with
the HHC and HHVMC cardioid condenser capsules.
Capsules from several other manufacturers are also
available for use with the HH: those with a 1.25” x 28
thread pitch and three contact rings. Condenser or
dynamic microphone capsules can be used to suit the
user’s preference or the application.
Encryption
When transmitting audio, there are situations where
privacy is essential, such as during professional
sporting events, in court rooms or private meetings.
For instances where your audio transmission needs
to be kept secure, without sacrificing audio quality,
Lectrosonics introduces Encryption Keys. Truly entro-
pic encryption keys are first created by a Lectrosonics
receiver, such as the DSQD Receiver. The key is then
synced with the DHu via the IR port. The audio will
be encrypted and can only be listened to if both DHu
and receiver have the matching encryption key. If you
are trying to transmit an audio signal and keys do not
match, all that will be heard is silence or white noise.
IR (infrared) Sync
An IR Sync Port is used for quick setup with receivers
that offer this feature. Settings for frequency, step size
and compatibility mode are transferred from receiver to
transmitter via the IR ports.
Side Button Functions
A programmable switch on the side of the housing can
be configured as a mute/cough switch, a power switch
or be disabled.
USB Port for Key Transfer and Firmware Updates
The encryption key is generated in the receiver, then
transferred to the transmitter via a USB port using a
cable. This requires that the user be in direct contact
with both units, which increases the security level.
Firmware updates are enabled by simply downloading
a file and utility program from the Lectrosonics web
site, connecting the transmitter to a computer via the
USB port and running the program.
