Lectrosonics UCR205d User Manual
UCR205D
DIVERSITY UHF RECEIVER
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
Rio Rancho, NM
www.lectrosonics.com
TABLE OF CONTENTS
GENERAL TECHNICAL DESCRIPTION ................................................................. 3
FRONT PANEL CONTROLS AND FUNCTIONS ..................................................... 6
REAR PANEL CONTROLS AND FUNCTIONS ....................................................... 7
ANTENNA USE AND PLACEMENT ........................................................................ 8
INSTALLATION AND OPERATING INSTRUCTIONS ............................................. 9
UCR205D REPLACEMENT PARTS and ACCESSORIES ...................................... 9
TROUBLESHOOTING ........................................................................................... 10
SPECIFICATIONS AND FEATURES .................................................................... 11
SERVICE AND REPAIR ........................................................................................ 12
RETURNING UNITS FOR REPAIR ....................................................................... 12
WARRANTY ............................................................................................ Back cover
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UHF Wireless Diversity Receiver
T
GENERAL TECHNICAL DESCRIPTION
The UCR205D 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 UCR205D 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 even if the two antennas are 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
FREQ
SWITCHES
AMP
uP
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
EXPANDER
EXPANDER
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
TREBLE
AUDIO
AMP
2:1
BASS
PILOT
TONE
MUTE
uP
TO DATA
DISPLAY
HEADPHONE
OUT
OUTPUT
LEVEL
ADJUST
3
XLR
OU
UCR205D
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 UCR205D 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 UCR205D 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 UCR205D 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 UCR205D design presents an elegantly simple, yet highly
effective solution to this age old problem. The UCR205D
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 presensitized 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
The UCR205D uses a pilot tone muting technique in order to
protect against the reception of stray signals. The Lectrosonics
transmitter adds an inaudible signal, known as the pilot tone, to
the transmitted signal. The receiver detects (and removes) the
pilot tone, and is thus able to identify the desired signal and
mute all others.
With the power switch in the normal (“ON”) position, receive
audio is muted unless a proper pilot tone is detected. The pilot
tone must be present for approximately one second before the
signal is accepted.
In the “PILOT OFF” position, received audio remains unmuted
regardless of the presence or absence of a pilot tone. This
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position is useful for locating a clear frequency, since any
potential interference may be heard. It may also be used in
situations where squelching behavior is undesirable. The “PILOT OFF” position disables the squelch, as described below.
SQUELCH
The UCR205D employs a sophisticated squelching system in
an attempt to deliver the cleanest possible audio during marginal conditions of reception. Any squelching system faces
inevitable trade-offs: squelch too much and valuable audio
information may be lost, squelch too little and excessive noise
may be heard; respond too rapidly and the audio sounds
“choppy”, respond too sluggishly and syllables or entire words
are cut off.
The UCR205D combines several techniques to achieve an optimal balance, removing distracting noise, without the squelching
action itself becoming a distraction. One of these techniques
involves waiting for a word or syllable to complete before
squelching. Another incorporates recent squelching history
and recent signal strength, adjusting squelching behavior dynamically for the most serviceable result under variable
conditions. Using these and other techniques, the UCR205D
can deliver acceptable audio quality from otherwise unusable
signals.
UHF Wireless Diversity Receiver
In the “PILOT OFF” position, the squelch system is disabled.
Received audio remains unmuted at all times with this setting.
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
–50dBm to –20dBm, the Mid position (center) allows an adjustment from –30dBm to 0dBm, and the Hi position sets the
audio output to a fixed +8dBm with no front panel control.
POWER SUPPLY
The UCR205D 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 if the power supply is disconnected for about 15 seconds.
Rio Rancho, NM – USA
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