Lectrosonics UDR200b User Manual

UDR200B

RATIO DIVERSITY UHF RECEIVER

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

Wireless Diversity Receiver

TABLE OF CONTENTS

GENERAL TECHNICAL DESCRIPTION ............................................................. 4

FRONT PANEL CONTROLS AND FUNCTIONS ................................................. 7

REAR PANEL CONTROLS AND FUNCTIONS ................................................... 8

INSTALLATION AND OPERATING INSTRUCTIONS ......................................... 9

USING THE LED INFORMATION DISPLAY ...................................................... 10

LecNet

FREQUENCY BLOCKS AND RANGES ............................................................ 14

TM

COMPUTER INTERFACE................................................................... 12

ANTENNA USE AND PLACEMENT................................................................... 15

TROUBLESHOOTING ......................................................................................... 16

UDR200B REPLACEMENT PARTS and ACCESSORIES................................ 16

SERVICE AND REPAIR ...................................................................................... 17

RETURNING UNITS FOR REPAIR .................................................................... 17

SPECIFICATIONS AND FEATURES .................................................................. 18

LecNet SOFTWARE PROTOCOL ...................................................................... 19

WARRANTY ........................................................................................... Back c over

Rio Rancho, NM – USA

3

GENERAL TECHNICAL DESCRIPTION

FILTER

AMP

1ST

LOCAL

OSCILLATOR

455KHZ

BP

FILTER

RATIO

COMBINER

&

OPTI-BLEND

455KHZ

BP

FILTER

2:1

EXPANDER

TREBLE

2:1

EXPANDER

BASS

23 KHZ

LP

FILTER

HEADPHONE

OUT

OUTPUT

LEVEL

ADJUST

XLR
OUT

PILOT
TONE
MUTE

FILTER

uP

AMP

FILTER

HI-LEVEL

DIODE MIXER

HI-LEVEL

DIODE MIXER

RF MODULE

2ND MIXER

&

IF AMP

2ND MIXER

&

IF AMP

50KHz

LP FILTER

50KHz

LP FILTER

XTAL

CONTROLLED

2ND

OSCILLATOR

RF LEVEL

LEDs

RF LEVEL

LEDs

SAW

FILTER

SAW

FILTER

70 MHz
IF AMP

70 MHz
IF AMP

COUNTING

DETECTOR

COUNTING
DETECTOR

FILTER

AMP

FILTER

AMP

FILTER

CENTER

FREQUENCY

DETECTOR

CENTER

FREQUENCY

DETECTOR

AUDIO

AMP

uP

UDR200B

BLOCK DIAGRAM

uP

RF
ONLY

TRI-MODE

DYNAMIC

uP

uP

uP

uP uP

VARIABLE

CUT-OFF

LP FILTER

TO DATA
DISPLAY

The UDR200B consists of two high performance, dual-conver­sion receivers operating simultaneously. The audio outputs of
the receivers are blended in a ratio controlled by the compara­tive RF levels in the receivers. The multistage RF front end is
a unique design that is tuned by a microprocessor to the
selected frequency. The RF and audio performance is ex­tremely stable over a very wide temperature range, making the
UDR200B perfectly suited to mounting in studio equipment
racks. The proprietar y audio processing includes a dual-band
compandor and dynamic noise filter 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 wide range, peak responding
LED indicators.

RF SECTION

The problem posed to the design staff was to retain the RF
reliability of the Lectrosonics’ fixed frequency designs but add
the frequency 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 ver y 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 12 transmission line resona­tors with variable capacitance applied to each resonator by a
microprocessor. This allows each resonator to be individually
tuned by the microprocessor 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.

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.

4

Wireless Diversity Receiver

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 (100 mW). The mixer in the UDR200B produces output at
only the sum and difference signals, with minimal spurious
signals. This mixer offers a very high overload threshold. 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 as our
fixed frequency designs. The mixer is followed by low noise
amplifiers and SAW filters to preserve the superior RF perfor­mance.

SURF ACE ACOUSTIC WAVE FILTER

The UDR200B 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 skir ts, 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 filter ing 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 quar tz, they are very temperature
stable. Conventional LC filters at these frequencies would drift
unacceptably in the elevated temperatures of an equipment
rack. After following the rule in a r igorous way, and due to the
sharp filter ing 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 UDR200B 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, par ticular ly 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 UDR200B design presents an elegantly simple, yet highly
effective solution to this age old problem. The UDR200B

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. The two resulting audio signals from the A and B re­ceiver channels are then combined to achieve the maximum
benefits of diversity reception.

RATIO COMBINING DIVERSITY WITH OPTI­BLEND

Instead of the usual audio switching between the two receiv­ers, we blend the audio outputs of the receivers in a ratio
controlled by the RF level of the received signals in the two
receivers. This totally eliminates any of the switching noise
sometimes heard in other designs and improves the signal to
noise ratio an additional 6 dB under weak signal conditions
and 3 dB in strong signal conditions.

TM

TRI MODE DYNAMIC FILTER

After being combined in the Opti-Blend circuit, 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 par ticular filter. We have satisfied ourselves
through elaborate tests that this filter is totally transparent.
There is one circumstance where a good argument can be
made for bypassing this filter, so a switch is provided to do just
that.

RF ONLY NOISE FILTER

A small switch on the rear of the receiver will allow the noise
filter to be set for RF ONLY. In this mode the filter is held out of

Rio Rancho, NM – USA

5

the audio frequency range unless the RF level drops to very
low levels. At weak RF levels, the filter operates in the TRI
MODE state until the RF level rises back to acceptable levels.
This has the desirable effect of softening dropouts. We recom­mend using the RF ONLY setting when it is desirable to pick up
high frequency background noise, such as for a location shot
for a movie. This might be machinery noise, compressed air,
etc. If the desirable background noise is at a low level, the Tri
Mode Dynamic Filter will identify this as undesirable hiss and
effectively remove it.

2:1 EXPANDER (Dual–Band Compandor)

“Dual-band Companding” is a complimentary system, that is,
whatever is done in the transmitter must be exactly mirrored in
the receiver. The transmitter compresses the audio signal in
two separate audio bands using four separate time constants
to avoid the inevitable trade-offs in attack and decay times that
occur in a single-band compandor. The companion circuit in
the receiver then re-expands this compressed signal restoring
the original dynamic range and frequency characteristics of the
signal.

The mixed audio signal leaves the Opti-Blend circuit and is fed
through a 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 2:1
expander. Each channel of the 2:1 expander is optimized for
its respective frequency band. By optimizing the compandors
for high and low frequencies we can handle sounds such as
clicks, sibilants and fast transients produced by plucked or
struck instruments in the high frequency section without com­promising the performance in the main voice range. The two
outputs of the 2:1 expander are then summed in an op-amp
and sent to an audio amplifier as one signal.

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 32.765 kHz tone is injected into the audio signal
after the microphone preamp, 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 detected, the receiver will remain open during all signal
conditions. If the transmitter signal degrades to the point
where hiss and noise may become objectionable, the Opti­Blend circuitry and Tr i Mode Dynamic Filter will work to reduce
or eliminate the unwanted noise. Since the pilot tone keeps
the receiver audio output open, as soon as the transmitter
signal returns to nor mal, the audio signal is instantly available
with no delays. A conventional squelch system, on the other
hand, can briefly interrupt the audio during a near drop-out
condition.

The pilot tone mute circuit drives a relay which physically
disconnects the output amplifier from the output audio trans-

former. The relay then connects the transformer primary to
ground to prevent hum pickup in the transformer due to an
open primar y winding. This provides complete muting of the
audio and the noise. The pilot tone function may be bypassed
with a rear panel push button. Once pushed, the pilot tone
mute is “latched” in a disabled condition until the receiver is
powered off then back on. When the pilot tone is disabled,
there is still a “squelching” function provided by the Opti-Blend
circuitry and Tri Mode Dynamic Filter. These circuits can
provide approximately 50 dB of muting during weak or no
signal conditions when the pilot tone is disabled. If you hear
moderate hiss when the transmitter is off, the pilot tone has
probably been bypassed.

AUDIO OUTPUT

The audio is a fully floating, transformer coupled, balanced
signal. Pin 2 is “high” or in phase with the transmitter input. A
precision attenuator allows you to adjust the output level from
+20 to -35 dBu. The output always runs “wide open” and is
only attenuated by this output level control. Neither the noise
level in the receiver nor headroom is affected. You can, how­ever, over drive or under drive attached audio equipment.

A ground lift switch is available to disconnect pin 1 of the 3 pin
XLR if a hum loop is encountered. Never, never cut off the
ground plug on the AC cable. The ground lift switch will ac­complish the same audio results without the safety hazard.

If a single ended output is necessary, pin 3 (or pin2) must be
tied to ground, preferably at the end of the cable with the single
ended connector. Other Lectrosonics equipment is not trans­former coupled and will work without the pin 3 ground connec­tion. This fully floating output will not.

The headphone output is a high quality signal derived from 4
high current op amps operating in parallel to provide a low
noise, low distortion signal. This output can be used as an
unbalanced output if needed. Unlike the rear panel balanced
output, this output can be overdriven if the headphone volume
control is set too high. As with any headphone output, keep
the sound levels in the headphones at a moderate level. When
the output is not being used, turn it all the way down. Be
careful to not turn up the headphone gain if the receiver is
muted or squelched. As with any output that is m uted, there is
no way of knowing what the level will be when the receiver
audio is opened.

6

Wireless Diversity Receiver

FRONT PANEL CONTROLS AND FUNCTIONS

TRANSMITTER AUDIO LEVEL

The modulation (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. The LED str ip is
fast enough to track even brief transients, easily exceeding the
response time of conventional VU meters.

RF LEVEL INDICATORS

Two separate LED strips are provided to indicate the level of
the incoming RF signals. The LED str ips 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 dual LED strips are especially useful in “trouble-
shooting” difficult antenna installations.

OPTI-BLEND LEDs

The UDR200B receiver operates with a method of audio ratio
blending of two audio outputs. RF level in each receiver is
compared and the audio signals from the two receivers are
mixed together in a ratio that favors the quieter receiver. As
this blending action occurs, the brightness of the two OPTI­BLEND LEDs will vary. The br ighter the LED, the more audio
is being mixed in from that receiver.

FULL INFORMATION DISPLAY

The UDR200B receiver includes a 16-segment LED character
strip that provides information about the selected frequency,
group, required transmitter setting, TV channel, assigned user
name, locked/unlocked status and pilot tone status.

PILOT INDICATOR

The audio output muting (squelch) function of the UDR200B is
controlled by a 33kHz tone modulation of the RF carrier. The
audio output is muted until this tone is present. The m uted
condition is indicated by a blinking TX switch setting in the LED
display.

The pilot tone function can be defeated by pressing a switch
on the rear panel. The PILOT indicator, however, operates the
same regardless of whether or not the defeat switch is
pressed. The PILOT indicator strictly indicates the presence of
the pilot tone carrier from the transmitter.

DIVERSITY MODE

This switch is set to the DIVERSITY position for normal opera­tion. For trouble-shooting or when the receiver is used with a
single antenna, the switch can be set to select a single an­tenna only.

MONITOR

This is an audio output to drive a wide variety of different types
of headphones. It is also usable as a second high quality
audio output to drive recorders or external audio devices.

POWER

Pressing the upper half of the rocker switch applies power to
the receiver. At turn on, there are various relays and delays
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 and/or the transmitter.

The UDR200B has a universal switching power supply which
will operate on AC voltages from 95 to 240Volts, 50 or 60Hz.

10

1uV

5

2 1mV

615.1

10

1uV

LECTROSONICS

5

2 1mV

UDR200B Front Panel

250

100

50

25

RF LEVEL

TX:B3 T

RF LEVEL

25

250

100

50

500

500

A

OPTI

BLEND

3

2

V

OPTI

BLEND

B

FREQ

SELECT

-48

MENU

-36

-42

TX AUDIO LEVEL dB

DIVERSITY

A B

MODE

-30

-18-24

Rio Rancho, NM – USA

-12

-6

MONITOR

LIM0

POWER

7