Lectrosonics UCR300 User Manual
UCR300
DIVERSITY UHF RECEIVER
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
www.lectrosonics.com
0885
Table of Contents
GENERAL TECHNICAL DESCRIPTION ........................................ 3
GENERAL TECHNICAL DESCRIPTION ........................................ 4
GENERAL TECHNICAL DESCRIPTION ........................................ 5
FRONT PANEL CONTROLS AND FUNCTIONS ........................... 6
REAR PANEL CONTROLS AND FUNCTIONS ............................. 7
ANTENNA USE AND PLACEMENT .............................................. 8
INSTALLATION AND OPERATING INSTRUCTIONS .................... 9
UCR300 REPLACEMENT PARTS and ACCESSORIES............... 9
FREQUENCY BLOCKS AND RANGES ...................................... 10
TROUBLESHOOTING ................................................................... 11
SPECIFICATIONS AND FEATURES ............................................ 12
SERVICE AND REPAIR .................................................. Back cover
WARRANTY .................................................................... Back cover
2
UHF Wireless Diversity Receiver
T
GENERAL TECHNICAL DESCRIPTION
The UCR300 is a portable, high performance, dual-conversion,
frequency synthesized, UHF receiver. The RF performance is
extremely stable over a very wide temperature range, making
the UCR300 perfectly suited to the rough environmental conditions found in the field. The proprietary audio processing
includes a dual-band compandor for very low distortion and a
superior signal to noise ratio. The squelch system is operated
by a separate pilot tone and mutes the audio output directly at
the output connector. The audio output is calibrated for exact
level matching, with a ten LED bar graph meter.
DIVERSITY RECEPTION
The antenna phase switching diversity technique was chosen in
order to keep the receiver compact enough for camera mounted
or shoulder bag applications. This diversity reception technique effectively minimizes dropouts in short range situations
where multi-path reflections can cause serious problems. The
optimum diversity reception is realized with the diversity antenna placed away from the receiver, however, dropouts are
significantly reduced with two antennas mounted directly on
the receiver.
RF SECTION
The problem posed to the design staff was to retain the RF
reliability of the Lectrosonics’ fixed frequency designs but add
the flexibility of a frequency agile design. The universal (and
poor) way to build frequency agile systems is to design a wide
open front end that will pass any frequency within the tuning
range of the system. This leads to very poor RF performance
with lots of interference, driving the user to switch frequencies
in an attempt to sidestep the interference. This makes frequency agile receivers a self fulfilling system; you have to use
the frequency agility to get away from the problems caused by
the frequency agile design compromises.
The problem of frequency agility is further compounded when
you realize that frequency changes “on the fly” cannot be made
on any type of wireless system. For example, if there is suddenly an interference problem with a system in use, on stage for
instance, a frequency change cannot be made without interrupting the program. Basically, the show must go on. In
multi-channel applications, changing the frequency of one sys-
tem will usually produce all kinds of new intermodulation
problems with the other systems operating in the same location.
Frequency agility is not the universal panacea for interference
problems. It is only another tool and a limited tool at that. The
first line of defense must be the system’s basic immunity to
interference. That required a new look at frequency agile receiver design.
FREQUENCY TRACKING FRONT-END
Our solution to the wide open front end problem was to design
a selective front end that can be tuned to the frequency in use.
Since we wanted this front end to be equivalent to our fixed
frequency front ends, this was a daunting task. Lectrosonics has
always used front ends with more sections and much more
selectivity than any other wireless manufacturer. The final
design consisted of a total of 6 transmission line resonators with
variable capacitance applied to each resonator by the hexadecimal switches.
This sophistication produced a front end that was as selective as
fixed frequency designs. The next step to improve the front end
was to use good old fashioned “brute force.”
HIGH CURRENT LOW NOISE AMPLIFIERS
The gain stages in the front end use some rather special transistors in a feedback regulated high current circuit that combine
three parameters that are generally at odds with one another.
These are: low noise, low gain and relatively high power. It is
easy to understand the advantages of low noise and high power
capability but why is low gain desirable? The answer is that in
a receiver, low gain allows the front end to handle stronger RF
signals without output overload, which is “increased headroom,” so to speak. The result of a design that takes all three of
these parameters into consideration at once, is a low noise RF
amplifier with a sensitivity rating equal or better than the best
conventional design with a hundred times less susceptibility to
intermodulation interference.
Combining the high power gain stages with the tracking front
end produces a receiver that is unusually immune to single and
multiple interfering signals close to the operating frequency
and in addition strongly rejects signals that are much farther
away.
ANTENNA
SWITCHING
RF MODULE
FILTER
SWITCHES
FREQ
uP
AMP
FILTER
uP
SYNTHESIZER
RF LEVEL
HI-LEVEL
DIODE MIXER
455KHZ
BP
FILTER
2ND MIXER
&
IF AMP
XTAL
CONTROLLED
2ND
OSCILLATOR
LEDs
COUNTING
DETECTOR
50KHz
LP FILTER
23 KHZ
LP
FILTER
VARIABLE
CUT-OFF
LP FILTER
SAW
FILTER
70 MHz
IF AMP
AMP
FILTER
VCO
FILTER
uP
2
E PROM
1ST
LOCAL
OSCILLATOR
Rio Rancho, NM – USA
BLOCK DIAGRAM
2:1
EXPANDER
TREBLE
2:1
EXPANDER
BASS
AUDIO
AMP
PILOT
TONE
MUTE
uP
HEADPHONE
OUT
OUTPUT
LEVEL
ADJUST
XLR
OU
TO DATA
DISPLAY
3
UCR300
GENERAL TECHNICAL DESCRIPTION
DOUBLE BALANCED DIODE MIXERS
In all wireless receivers, a mixer is used to convert the carrier
frequency to the IF frequency where most of the filtering and
gain in the receiver takes place. After doing all the right things
in the front end, it would be a shame to waste the performance
with a second rate mixer. In other designs that is exactly what
happens since mediocre mixers cause more intermodulation
problems than mediocre front ends. The only solution was a
high power, double balanced diode mixer driven by a local
oscillator with more output power than most wireless transmitters (50 mW). The mixer in the UCR300 produces output at
only the sum and difference signals, with minimal spurious
signals. This mixer offers a very high overload threshold and a
high degree of isolation between ports. The IF output of this
mixer is at 71 MHz which is unusually high for a wireless
receiver. This high frequency was chosen to increase the image
rejection in the front end to as high or a higher level than our
fixed frequency designs. The mixer is followed by high current,
low noise amplifiers and SAW filters to preserve the superior RF
performance.
SURFACE ACOUSTICWAVE FILTER
The UCR300 is unique in that it uses state of the art SAW filters in
each IF section. The SAW filters are the only filter that can
combine sharp skirts, constant group delay, and wide bandwidth in
one filter. Though expensive, this special type of filter allows us to
follow the basic receiver rule of doing the primary filtering as early
as possible, at as high a frequency as possible and before high gain
is applied to the signal. Since these filters are made of quartz, they
are very temperature stable. Conventional LC filters at these
frequencies don’t begin to perform as well and in addition would
drift unacceptably in the elevated temperatures of an equipment
rack. After following the rule in a rigorous way, and due to the
sharp filtering action of the SAW filters, the 71MHz signal is
converted to the low frequency of 455 kHz. Lots of gain is then
applied in a conventional IC and the signal is then converted to
audio. 455 kHz is very unconventional for a second IF in a wide
deviation (±50 kHz) system. We chose to use 455 kHz to obtain an
outstanding AM rejection figure over a very wide range of signal
strengths and to produce an excellent noise improvement at low
signal strengths (capture ratio). To use an IF at 455 kHz requires
an unusual circuit to convert the IF to audio.
DIGITAL PULSE COUNTING DETECTOR
The UCR300 receiver uses an advanced digital pulse detector to
demodulate the FM signal, rather than a conventional quadrature
detector. The common problem with quadrature detectors is thermal drift, particularly those that operate at higher frequencies like
10.7 MHz. Though the quadrature detectors may work well at
room temperature, if they are not carefully compensated, they will
produce amplitude changes and audio distortion in the elevated
temperatures of an equipment rack. Some manufacturers try to get
around the problem by tuning their systems at higher temperatures
after they’ve been on for some time. This just means that for the
first hours in a cool room the receiver is well out of specification or
after a few hours in a hot rack.
The UCR300 design presents an elegantly simple, yet highly
effective solution to this age old problem. The UCR300 detector
basically works like this: A stream of precision pulses is generated at 455KHz locked to the FM signal coming from the 455
kHz IF section. The pulse width is constant, but the timing
between pulses varies with the frequency shift of the FM signal.
The integrated voltage of the pulses within any given time
interval varies in direct proportion to the frequency modulation
of the radio signal. Another way of describing it is that as the
FM modulation increases the frequency, the circuit produces
more pulses and as the modulation decreases the frequency, the
circuit produces fewer pulses. More pulses produces a higher
voltage and fewer pulses a lower voltage. The resultant varying
voltage is the audio signal.
This type of detector eliminates the traditional problems with
quadrature detectors and provides very low audio distortion, high
temperature stability and stable audio level. The counting detector
also adds additional AM rejection, in addition to the limiting in the
IF section. The amplitude of the pulses is constant, so level
differences in the IF signal do not affect the pulse.
TRI MODE DYNAMIC FILTER
The audio signal is passed through a “dynamic noise reduction
circuit”. The cutoff frequency of this filter is varied automatically
by measuring the amplitude and frequency of the audio signal and
the quality of the RF signal. The audio bandwidth is held only to
that point necessary to pass the highest frequency audio signal
present at the time. If the RF level is weak, then the filter becomes
more aggressive. This results in a dramatic reduction of “hiss” at
all times. During passages with a high frequency content, this
filter gets completely “out of the way” and passes the signal with
no decrease in high-frequency response. Keep in mind that if hiss
is added to a signal, there is a psycho acoustic effect that makes
the sound seem brighter. The other side of this is that if hiss is
removed from a signal it will sound duller. Basically the ear’s
detection apparatus is pre-sensitized to high frequency sounds by
small amounts of high frequency hiss. Consider this effect when
making a judgment about the sound quality of various wireless
systems and this particular filter. We have satisfied ourselves
through elaborate tests that this filter is totally transparent.
PILOT TONE MUTE (SQUELCH)
The 300 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.
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GENERAL TECHNICAL DESCRIPTION
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 tone function may
be bypassed with the Pilot Tone Disable switch (located on the
front panel.) When the pilot tone has been disabled with this
switch, the Pilot LED will glow red and the MOD function of
the LED bargraph meter on the front panel is disabled. The
Pilot LED on the front panel will glow green 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 Lo/Mid/Hi range switch (located on
the back panel.) In the Lo position the adjustment range is from
–50dBu to –20dBu, the Mid position (center) allows an adjustment from –30dBu to 0dBu, and the Hi position sets the audio
output to a fixed +8dBu with no front panel control.
POWER SUPPLY
The UCR300 may be operated from an external 10 to 16.5 VDC
source. The power supply has a built in Poly-Fuse to protect the
unit. This fuse resets by simply disconnecting the power supply
for about 15 seconds.
UHF Wireless Diversity Receiver
Rio Rancho, NM – USA
5
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