Lectrosonics UT195 - Manual (Page 5)

The audio signal leaves the Detector circuit and is fed through an
amplifier to the 23 kHz Low Pass Filter where all the high frequency
noise (including the 32 kHz pilot tone) is filtered out. After the 23
kHz low pass filter, the signal is split into two parts via a 1 kHz low
pass filter and a 1 kHz high pass filter. The separated signals are
then processed in separate channels of the NE572 2:1 Expander.
Each channel of the 2:1 Expander is optimized for its respective
frequency band. The two outputs of the 2:1 Expander are then
summed in an op-amp summer and sent to the output amplifier as
one signal.
PILOT TONE MUTE (SQUELCH)
The 195 system utilizes a separate ultrasonic tone modulation of the
basic carrier to operate the receiver squelch. In the transmitter, a
32kHz tone is injected into the audio signal path just after the
compandor. The supersonic pilot tone is filtered out of the audio
signal immediately after the detector in the receiver so that it does
not influence the compandor or various gain stages.
The basic benefit of the pilot tone squelch system is that the receiver
will remain squelched (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. Once a pilot tone is received, the
receiver will remain open during all signal conditions.
The mute circuit drives a relay which physically disconnects the
output amplifier from the output. This provides complete muting of
the audio and the noise. The Pilot LED on the front panel will glow
when the pilot tone has enabled the receiver audio output.
OUTPUT LEVEL ADJUST AND RANGE SWITCH
The front panel Output control will adjust the audio output within
the range set by the VAR/FIX range switch (located on the back
panel.) In the VAR position the adjustment range is from –30dBm
to 0dBm, and the FIX position sets the audio output to a fixed
+8dBm with no front panel control.
POWER SUPPLY
The UR195 may be operated from the supplied CH12 adapter, or
from an external 12 to 18 VDC source. The power supply has a
built in Poly-Fuse to protect the unit. This fuse is self healing by
simply turning off the receiver for about 15 seconds.
FRONT PANEL CONTROLS AND FUNCTIONS
PWR LED
When lit, this LED indicates that power is applied to the UR195 and
adequate voltage is present to operate the unit.
PILOT LED
The audio output muting (squelch) function of the UR195 is
controlled by a 32kHz tone modulation of the RF carrier. The audio
output is muted until this tone is present. This LED will remain on
as long as the receiver audio is enabled by the pilot tone.
TRANSMITTER AUDIO LEVEL METER
When the meter function switch is in the Mod position, the modula­
tion (audio level) of the incoming signal is indicated by a fast
responding LED strip. The strip is calibrated in 6dB steps over an
expanded scale (54dB) which provides an extremely accurate visual
“picture” of the signal dynamics, even at a distance away from the
receiver. Audio signal peaks easily exceed the response time of VU
meters, however, the LED strip is fast enough to track even brief
transients.
RF LEVEL INDICATORS
With the function switch in the RF position, the LED strip indicates
the level of the incoming RF signals. The LED strips are calibrated
to provide accurate indications from 1uV to 1mV. The LEDs are
highly visible from a distance, making antenna set up more accurate.
The LED strip is especially useful in trouble-shooting difficult
antenna installations.
MONITOR
This is a high quality audio output to drive a wide variety of
different types of headphones. It is also useable as a secondary
audio output to feed recorders or external audio devices. The
Monitor jack is a mini stereo type with the same signal applied to
the tip and ring contacts. Stereo or mono headphones may be used
without any loss of volume or damaging the UR195.
POWER SWITCH
This slide switch, and its corrosponding LED indicator, switches the
receiver from Off to On. At turn on and off there is a delay built
into the receiver to allow various stages to stabilize before the audio
output is activated. This will prevent an audio “thump” when
powering up the receiver.
AUDIO OUTPUT
The front panel Output control will adjust the audio output within
the range set by the VAR/FIX range switch (located on the back
panel.) In the VAR position the adjustment range is from –30dBm
to 0dBm, and the FIX position sets the audio output to a fixed
+8dBm with no front panel control.
MONITOR
MOD
1mV 10uV
42
RF
1uV
36 30
PWR
100uV
12 18 24 6 0dB
OFF
PILOT
AUDIO
OUTPUT
ON
Figure 2 - UCR195 Front Panel
Rio Rancho, NM – USA 5