Lectrosonics UCR310 User Manual
UCR310
DIVERSITY UHF RECEIVER
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
www.lectrosonics.com
0885
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
UCR310 REPLACEMENT PARTS and ACCESSORIES ...................................... 9
FREQUENCY BLOCKS AND RANGES .............................................................. 10
TROUBLESHOOTING ......................................................................................... 11
SPECIFICATIONS AND FEATURES .................................................................. 12
SERVICE AND REPAIR ........................................................................ Back cover
WARRANTY ........................................................................................... Back cover
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UHF Wireless Diversity Receiver
T
GENERAL TECHNICAL DESCRIPTION
The UCR310 is a portable, high performance, triple-conversion,
frequency synthesized, UHF receiver. The RF performance is
extremely stable over a very wide temperature range, making the
UCR310 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 Smart Squelch system is operated by a separate
pilot tone and mutes the audio output directly at the output connector.
DIVERSITY RECEPTION
The antenna phase SMART 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 system 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 consists of a total of
4 transmission line resonators with variable capacitance applied to
each resonator by the hexadecimal switches.
This sophistication produces a front end that is as selective as fixed
frequency designs. The next step to improve the front end is to use
good old fashioned “brute force.”
HIGH CURRENT LOW NOISE AMPLIFIERS
The gain stage in the front end uses a rather special transistor in a
feedback regulated high current circuit that combines 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 stage 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.
RF MODULE
ANTENNA
SWITCHING
uP
uP
FREQ
SWITCHES
Smart Diversity
FILTER
SYNTHESIZER
UCR310
3RD MIXER
AND
IF AMP
XTAL
3rd
OSCILLATOR
RF LEVEL
LEDs
COUNTING
DETECTOR
50KHz
LP FILTER
23 KHZ
LP
FILTER
VARIABLE
CUT-OFF
LP FILTER
EXPANDER
EXPANDER
SAW
FILTER
HI-LEVEL
DIODE MIXER
2ND
MIXER
10.7 MHZ
CONTROLLED
71 MHz
IF AMP
AMP
FILTER
1ST
LOCAL
OSCILLATOR
FILTER
2
E PROM
2nd
VCO
Smart Squelch
FILTER
uP
Rio Rancho, NM – USA
BLOCK DIAGRAM
2:1
TREBLE
AUDIO
AMP
2:1
BASS
PILOT
TONE
MUTE
uP
TO DATA
DISPLAY
OUTPUT
LEVEL
ADJUST
XLR
OU
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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
UCR310 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 ACOUSTIC WAVE FILTER
The UCR310 is unique in that it uses a state of the art SAW filter in
the IF section. The SAW filter is 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 10.7Mhz and then to the low frequency of 300 kHz.
Lots of gain is then applied in a conventional IC and the signal is
then converted to audio. 300 kHz is very unconventional for a
second IF in a wide deviation (±50 kHz) system. We chose to use
300 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
300 kHz requires an unusual circuit to convert the IF to audio.
DIGITAL PULSE COUNTING DETECTOR
The UCR310 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 UCR310 design presents an elegantly simple, yet highly effective solution to this age old problem. The UCR310 detector
basically works like this: A stream of precision pulses is generated
at 300kHz locked to the FM signal coming from the 300 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
The UCR310 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.
When the receiver is powered up, 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.
If the PILOT TONE BYPASS button is pressed, received audio
remains unmuted regardless of the presence or absence of a pilot
tone. This 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
TONE BYPASS” disables the squelch, as described below.
SMART SQUELCH
The UCR310 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; re-
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spond too rapidly and the audio sounds “choppy”, respond too
sluggishly and syllables or entire words are cut off.
The UCR310 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 UCR310 can deliver acceptable audio quality from
otherwise unusable signals.
In the “PILOT TONE BYPASS” mode, 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 -20/0/+8 range switch (located on the back
panel.) In the -20 position the adjustment range is from –50dBm to
–20dBm, the 0 position (center) allows an adjustment from –
30dBm to 0dBm, and the +8 position sets the audio output to a
fixed +8dBm with no front panel control.
UHF Wireless Diversity Receiver
POWER SUPPLY
The UCR310 may be operated from an external DC source (see
Specifications and Features section for allowed voltages.) 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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