Download UR4D RECEIVER

RF Sub System General Description
The receiver RF Sub System consists of all of the hardware needed to receive the wireless radio signal and convert it
into audio. It can be broken down into several sub-components: the antenna system, the front end, mixer, 1st IF, 2nd
IF and detector. Each has an important part to play in determining the overall performance of the product. The UR4
receiver has two BNC input connectors, and will be supplied with a pair of detachable 1/2 wave antennas that can be
remoted using accessory 50-Ohm cables if desired. Both single and dual receivers will use Shure’s MARCAD diversity
for unsurpassed protection against signal dropouts.
UR4S and UR4D RF sections are located on the 190-044 main board. Each receiver channel in a UR4 system contains
two RF sections referred to as sections A and B. Dual channel systems like the UR4D will contain 4 RF sections and
will be referred to by CH1A, CH1B, CH2A, and CH2B. Single channel systems like the UR4S will use the CH2A and
CH2B part of the 190-044 main board.
RF signals enter the UR4 receiver at the BNC ports labeled Antenna A In and Antenna B In. The receiver provides
+12.4 VDC @ 150 mA at each antenna port for use with external RF amplifiers. Up to two external line amps, or one
line amp and one active antenna can be driven from each antenna port. Power to the antenna ports can be removed
via jumper settings on the 190-044 main board. UR4D systems passively split the signals present at each antenna port
and send them equally to channels 1 and 2. UR4S systems send antenna signals directly to channel 2 without splitting.
Receiver channels 1 and 2 are identical so operational descriptions of a single receive channel may be applied equally
to both channels in a UR4D system.
Each RF channel requires +15V and +5V from the power supply.
Each channel frequency is user adjustable from the 190-046 display board. Several signals are derived from the channel
frequency are used to automatically tune the RF section. The following tuning related signals are input to the RF section
from the 190-045 microprocessor board: [(digital signals) Clock, Data, Load enable], [(DAC signals) VCO course Tune
voltage, Track tune filter voltage].
The front end incorporates two track-tuned filters for superior protection from unwanted signals, while providing an
industry leading 60 MHz of frequency coverage per SKU (slightly more in the higher frequency bands). Conversion to
the 1st IF is accomplished through a double balanced mixer to provide greatly improved RF dynamic range and system
compatibility. The design also uses a 1st IF frequency of 110.6 MHz, together with a narrow SAW (Surface Acoustic
Wave) filter, to minimize spurious (unwanted) receiver responses. The Saw filter is followed by a 1St IF amp and 2 pole
band-pass filter, providing improved sensitivity and second image rejection.
The 2nd IF consists of an integrated amplifier and mixer coupled with a discreet designed 99.9 MHz crystal oscillator.
The outputs from both 1st and 2nd local oscillators are shared between RF sections A and B. Demodulation produces
the following baseband information signals: Audio (with Tonekey), and Noise. Each RF channel outputs the following
respective information signals to the audio section of the 190-044 main board: Audio A, Audio B, Noise A, Noise B. A
32kHz ASK Tonekey signal is embedded within the audio signal and will be filtered and demodulated in the audio
section of the 190-044 main board.
After conversion to the 2nd IF, the signal level present in each RF section is detected. A DC signal proportional to the
2nd IF level is created and referred to as the received signal strength indicator or RSSI. When antenna signals are within
the receiver’s normal operating range the RSSI is displayed by a string of six LEDs on the 190-046 display board.
Antenna signals that exceed the maximum dynamic range of the receiver are detected in each 2nd IF section by
separate RF overload circuitry. A DC signal proportional to the RF overload level is generated and used to activate a
RF overload LED on the 190-046 display board. Each RF channel outputs the following respective DC signals to the
190-045 microprocessor board: RSSI A, RSSI B, RF overload A, RF overload B.
25-1099 (Rev. 1)
10