Frequency Agile UHF Miniature Belt-Pack Transmitter
MODULATION LEDS
Indicate the proper setting of the MIC LEVEL control. There are two bicolor modulation LEDs that can light either red or
green.
“-20dB level” One modulation LED glows green and the transmitter is 20 dB below full modulation.
“-10 dB level” Both modulation LEDs glow green and the transmitter is close to full modulation.
“+0 dB level” -20 LED glows red and the -10 LED glows green. The transmitter is in slight limiting and is fully
modulated. This is probably desirable. See the discussion below.
“+10 dB level” Both LEDs are red. The transmitter is in limiting and you may want to reduce the transmitter audio
gain. See the discussion below.
The 400 series transmitters employ a digitally-controlled analog audio limiter just before the analog-to-digital
converter. The limiter has a range of more than 30dB 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.
The audio level LEDs indicate limiter activity. The first red LED indicates that the limiter is active and that the
transmitter is fully modulated (audio level is between +0 and +10 dB). The second red LED indicates that the
level is 10dB or more into limiting. Occasional forays into the red are desirable for most applications, since the
distortion introduced by the limiter is so minimal, and full modulation is thus assured. We strongly recommend
setting the gain of the transmitter high enough so that the first red LED occasionally lights.
Generally speaking, some limiting is desirable in normal operation to improve the signal to noise ratio of the
system. The limiting action is not audible and does not create distortion. A highly trained ear would hear only
the compression of the peaks in the audio signal, which is desirable with most recorders and many sound
reinforcement systems.
AUDIO LEVEL
Used to adjust the audio input level for the proper modulation.
ANTENNA
The flexible bronze cable antenna supplied with the transmitter is cut to 1/4 wavelength of the center of the frequency
block (the frequency range) of the transmitter. It is removable via an SMA connector. The SMA connector is a
50 Ohm RF port which can also be connected directly to test equipment. Replacement antennas are available in
pre-cut lengths for specific frequency blocks, or as a kit with instructions to cut the antenna for any frequency block.
THE BELT CLIP
The belt clip may be removed for special applications by gently spreading the spring wire clip and pulling the ends
out of the holes in the case. The clip can be installed in two positions so that when worn, the antenna can be point-
ing up or down.
Rio Rancho, NM – USA
7
(16 pages)
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