Lectrosonics UCR200d User Manual
UCR200D
DIVERSITY UHF RECEIVER
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
Rio Rancho, NM
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
UCR200D REPLACEMENT PARTS and ACCESSORIES.............. 9
FREQUENCY BLOCKS AND RANGES ........................................ 10
TROUBLESHOOTING.................................................................... 11
SERVICE AND REPAIR.................................................................. 12
RETURNING UNITS FOR REPAIR ................................................ 1 2
SPECIFICATIONS AND FEATURES ............................................. 13
WARRANTY .................................................................... Back cover
2
UHF Wireless Diversity Receiver
R
T
GENERAL TECHNICAL DESCRIPTION
The UCR200D 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
UCR200D 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 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 consisted of a total
of 6 transmission line resonators with variable capacitance applied
to each resonator by the hexadecimal switches. This allows each
resonator to be individually tuned by the hexadecimal switches for
any user selected frequency in a 25 MHz band.
This sophistication produced a front end that was as selective as
fixed frequency designs, yet could cover the entire 25 MHz range.
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.
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
ANTENNA
SWITCHING
RF MODULE
FILTER
uP
AMP
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
SAW
FILTER
70 MHz
IF AMP
AMP
FILTER
uP
FILTER
1ST
LOCAL
OSCILLATOR
uP
Rio Rancho, NM – USA
BLOCK DIAGRAM
EXPANDER
VARIABLE
CUT-OFF
LP FILTER
EXPANDER
2:1
TREBLE
2:1
BASS
AUDIO
AMP
PILOT
TONE
MUTE
uP
TO DATA
DISPLAY
HEADPHONE
OUT
OUTPUT
LEVEL
ADJUST
XL
OU
3
UCR200D
GENERAL TECHNICAL DESCRIPTION
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
UCR200D 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 UCR200D 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 gr oup 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 (±75 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 UCR200D 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 oper ate at higher frequencies like
10.7 MHz. Though the quadrature detectors may work well at
room temperature, if they are not carefully compensa ted, 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 tha t 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 UCR200D design presents an elegantly simple, yet highly
effective solution to this age old problem. The UCR200D detector
basically works like this: A stream of precision pulses is g enerated 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 200 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 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.
4
GENERAL TECHNICAL DESCRIPTION
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 UCR200D may be operated from the supplied CH20 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 disconnecting the power supply for about 15 seconds.
UHF Wireless Diversity Receiver
Rio Rancho, NM – USA
5
Loading...