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Ritron Patriot SST-444 Operational Description

Uhf-fm handheld transceiver
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TYPE OF EXHIBIT:
FCC PART:
MANUFACTURER:
MODEL:
TYPE OF UNIT:
FCC ID:
DATE:
Included in this exhibit is the operating instructions and theory of operation for the SST-444.
The operating instructions and theory of operation included in this exhibit are excepts of the Maintenance
and Operating Manual for RITRON Model Patriot SST-444 UHF-FM Handheld Transceiver. The complete
Maintenance and Operating Manual is included with this application for Certification as a separate exhibit.
Signed:
Michael A. Pickard - Project Engineer
OPERATIONAL DESCRIPTION
2.1033 (c)(3)
RITRON, INC.
505 West Carmel Drive
Carmel, IN 46032
SST-444
UHF-FM Handheld Transceiver
AIERIT13-450
July 7, 2000

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Summary of Contents for Ritron Patriot SST-444

  • Page 1 The operating instructions and theory of operation included in this exhibit are excepts of the Maintenance and Operating Manual for RITRON Model Patriot SST-444 UHF-FM Handheld Transceiver. The complete Maintenance and Operating Manual is included with this application for Certification as a separate exhibit.

  • Page 2: Description Of Controls And Connectors

    This jack is also used to program the radio using the optional PC programming kit. Charge Jack The battery may be charged through this jack using a standard RITRON wall socket charger cube. This jack also connects microphone audio to the optional remote speaker/microphone.
  • Page 3 DESCRIPTION OF CONTROLS AND CONNECTORS Antenna Jack Cover Vol Down/Off Audio Accessory Jack On/Vol Up Charge Jack Push-to-Talk Speaker Channel Selector Microphone Battery Access Door (Case bottom) Battery Charger Contacts (Case bottom) Fig. 2 Controls and Accessory Connectors Belt Clip Installation If you are going to attach the belt clip to the handheld, follow these instructions: 1) The belt clip is fastened to the radio case back with the Philips head screw provided.

  • Page 4: Operation

    OPERATION On-off/Volume To switch on the radio - press the on/volume up button. To adjust the volume - press the volume up button until you reach the desired level. You should hear noise and any broadcasts on the channel. To turn off the radio - press and hold the off/volume down button until two tones sound. To determine whether the radio is on - press the volume down button.

  • Page 5: What The Radio Tones Mean

    Turn off the radio and try again. A long, low-pitched tone means the battery voltage is too low to operate the radio. In this case, recharge the battery. If you cannot correct a problem, consult an authorized Ritron service facility or Ritron.
  • Page 6 OPERATION OPTIONAL RADIO TONES The SST-444 can be programmed using the RITRON PC Programmer for optional alert tones. Receive Squelch Tone A short tone sounds at the end of each received transmission to indicate that you may transmit. Busy Channel Transmit Inhibit If a user is transmitting on your radio frequency without your tone, you will not be allowed to transmit.

  • Page 7: Power Supply And Voltage Distribution

    SST-444 THEORY OF OPERATION INTRODUCTION The SST-444 is a four-channel handheld transceiver built on a single multi-layer printed circuit board. Both sides of the main printed circuit board are populated with components, with the bottom side containing only surface mounted components. The SST-444 is frequency synthesized, with all functions of the radio controlled by microcontroller.

  • Page 8: Reference Oscillator

    SST-444 THEORY OF OPERATION REFERENCE OSCILLATOR Reference oscillator Y302 is a 1.5 ppm temperature controlled, voltage controlled oscillator (TCVCXO) operating at 14.4 MHz. The Pin 4 output of the TCVCXO provides a reference for the frequency synthesizer IC401 at Pin 20. IC401 is programmed to provide an output at Pin 1 that is ¼ of the reference (3.6 MHz), which is applied as a reference oscillator to Pin 27 of IC301 microcontroller.

  • Page 9: Digital Potentiometers

    SST-444 THEORY OF OPERATION VCO / Buffer Amplifiers Q403, L401, CR402 and associated components form the VCO (Voltage Controlled Oscillator), a resonant circuit that oscillates at frequencies from 416 MHz in receive (receive frequency - 43.65 MHz) to 470 MHz in transmit.
  • Page 10 SST-444 THEORY OF OPERATION RECEIVER As mentioned before, Q101 switches the regulated +5 VDC to the receiver. The +VRX receiver voltage is switched at the strobe duty cycle if programmed for power strobe. RF Amplifier A received signal from the antenna passes through a low-pass filter (L207, C216, C217, L206, C101, and C202) to the receiver headend.
  • Page 11 SST-444 THEORY OF OPERATION Voice Band Bilateral switch IC304A passes the received audio signal to the input of IC303C, which along with its associated components for a high-pass filter/amplifier circuit that attenuates audio signals below 300 Hz. The output of IC303C is applied to the input of IC305B limiting amplifier. Bilateral switch IC304B is switched in receive to insert C351 into the feedback circuit of IC305B, providing de-emphasis of the received audio signal.
  • Page 12 SST-444 THEORY OF OPERATION TRANSMITTER Keying The SST-444 transmitter is keyed when PTT switch SW304 is depressed. Electret condenser microphone M301 is connected in series to ground with the PTT switch, which when depressed draws current through M301, SW304, CR304 and R307 to turn on pass transistor Q302. Q302 then turns on Q301 to pull the TX Key Pin 2 input of microcontroller IC301 low.
  • Page 13 SST-444 THEORY OF OPERATION Sub-Audible Microcontroller IC301 generates the sub-audible selective signaling encode waveforms at Pin 21 and applies them to the input of buffer amplifier IC305A. The output of IC305A is applied to the input of IC308, a 5-pole low-pass filter that attenuates frequencies above 250 Hz. C342 and C343 set the corner frequency of the low-pass filter, with C342 switched in by Pin 7 of IC301 to lower the corner frequency for lower tones.
  • Page 14 SST-444 THEORY OF OPERATION DESCRIPTION +V SW output is HIGH when the radio is turned on, keeping pass transistor Q304 turned on via Q303 to supply power to the radio. GROUND sets the upper reference level for the A/D and is connected to the regulated +5 VDC. REFH A/D input BATTERY is used to measure the battery voltage for low and dead battery detection.

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