1. SN-553 Frequency Synthesizer
CECOM LAR Course
Logistics Assistance Division
Fort Monmouth, New Jersey
This class will cover the SN-553 Frequency Synthesizer.

2. Purpose
Provides the Local Oscillator Frequency of 4.47 to 5.07 GHz for the Up and Down Converters
Recap slide
Please note that the AN/TRC-170(V)2 system has two (2 ea..) Dual Frequency Synthesizers installed and the AN/TRC-170(V)3 system has one (1 ea..) Dual Frequency Synthesizer installed.

3. Reference Loop Block Diagram
Now lets discuss the Reference Loop Signal Flow through the Frequency Synthesizer. Please refer to FO There are three phase locked loop circuits that make up the frequency synthesizer. These 3 circuits are explained below;
1. The Reference Loop
J4 is the input from the Tropo Modem. This is a 10 MHz signal coming from the Rubidium Standard. This is the base frequency, which drives all the frequencies used in the synthesizer.
A9 Module: Is a highly stable 100 MHz Reference Oscillator. It turn, it sends a 100 MHz signal to the A8. It gets a AFC correction voltage from the A7.
A8 Multiplier CCA: Takes the 100 MHz and splits it. The first 100 MHz is sent to the A7, which completes the phase lock loop for the 100 MHz oscillator. The second 100 MHz is multiplied to 4.6 or 4.8 GHz and routes these signals to the A3 & A4 RF Converter CCA. If an error occurs on the A8 CCA it will illuminate DS4 on the A7 Reference Card.
A7 CCA: The Reference Circuit Card receives the 100 MHz signal from the A8 and divides it by 10 to produce a 10 MHz signal. The Phase Detector compares this 10 MHz to the 10 MHz from the Rubidium Standard and a resultant error correction voltage called AFC is sent to the A9. The 10 MHz is divided down to 1 MHz. This 1 MHz signal is routed to the A5 & A6. If a failure happens in this circuitry, it will illuminate DS1 on the A7 CCA.

4. Transmit Loop Block Diagram
Now lets take a look at the Transmit Loop. Please refer to Figure FO 12-1.
The Transmit Loop
1. A1 Module: The transmit Loop starts with the A1 module, the cavity-tuned oscillator. The output of the VCO is set by thumbwheel switch S1. It is adjusted on the front panel knob labeled “Tuned”. The oscillator gets an input voltage from the A5. This voltage is proportional to the frequency that is set to the thumb-wheel switches on the front panel. When properly tuned, the output of this oscillator is 70 MHz above the desired frequency. If 4.4 GHz is set on the front panel then the output of the oscillator will be 4.47 GHz. The output of this oscillator is routed to the A3.
2. A5 IF CCA: Gets a logic input from S1 {Transmit Frequency}. This logic input is converted to voltage and sent to the A1. It compares the 100 to 300 MHz from the A3 to the 1 MHz from the A7. The result of this phase error is displayed on the front panel M1. If the frequencies cannot be phase lock, DS2 is illuminated. If a frequency that is out of the 4.4 to GHz, DS1 on the front panel will illuminate and only DS1.
3. A3 RF Converter Module: The 4.47 to 5.07 GHz Local Oscillator (LO) signal from the A1 is received by the A3 module. Here the 4.47 to 5.07 GHz Local Oscillator (LO) signal is mixed with the 4.6 or 4.8 GHz signal from the A8 module that was selected by the decoder circuit to produce a MHz IF output. This MHz is then sent to the A5 to be used in the reference loop to make the 1 MHz which will eventually become your OSC AFC voltage. This completes the transmit phase lock circuit. The second output of the A3 module goes to a 20 dB isolator, then to the 2 dB pad AT1 where it is routed to the Up Converter. If this output level is not +13 dBm 2 dB, then DS5 is illuminated. Back to the directional coupler, one of the ports is routed to a mixer where it is mixed with the 4.6 or 4.8 GHz frequency from the A8.

5. Receive Loop Block Diagram
Now lets take a look at the Receive Loop. Please refer to Figure FO 12-1.
The Receive Loop
1. A2 Module: The Receive Loop starts with the A2 module, the cavity-tuned oscillator. The output of the VCO is set by thumbwheel switch S2. It is adjusted on the front panel knob labeled “Tuned”. The oscillator gets an input voltage from the A6. This voltage is proportional to the frequency that is set to the thumb-wheel switches on the front panel. When properly tuned, the output of this oscillator is 70 MHz above the desired frequency. If 4.4 GHz is set on the front panel then the output of the oscillator will be 4.47 GHz. The output of this oscillator is routed to the A4.
2. A6 IF CCA: Gets a logic input from S2 {Receive Frequency}. This logic input is converted to voltage and sent to the A2. It compares the 100 to 300 MHz from the A4 to the 1 MHz from the A7. The result of this phase error is displayed on the front panel M1. If the frequencies cannot be phase lock, DS3 is illuminated. If a frequency that is out of the 4.4 to GHz, DS2 on the front panel will illuminate and only DS2.
3. A4 RF Converter Module: The 4.47 to 5.07 GHz Local Oscillator (LO) signal from the A2 is received by the A4 module. Here the 4.47 to 5.07 GHz Local Oscillator (LO) signal is mixed with the 4.6 or 4.8 GHz signal from the A8 module that was selected by the decoder circuit to produce a MHz IF output. This MHz is then sent to the A6 to be used in the reference loop to make the 1 MHz which will eventually become your OSC AFC voltage. This completes the receive phase lock circuit The output level at this point is +11 to + 15 dBm and is routed to the Down Converters. Back to the directional coupler, 1 port on the directional is feed to a level detector. If the level is not +13 dBm 2 dB DS6 is illuminated. Back to the directional coupler, one of the ports is routed to a mixer where it is mixed with the 4.6 or 4.8 GHz frequency from the A8.

6. Transmit Loop BITE Circuitry Block Diagram
Now lets take a look at the Transmit Loop BITE Circuitry and discuss the conditions that causes these BITE LEDs to activate. Refer to FO 12-1 above.
1. There are five faults that will cause the TX Summary LED DS1 to activate on the front panel. These five conditions are listed below. The A7 CCA contains internal fault LED indications for the Transmit Loop.
2. DS5: The first fault indicates that the power out of the VCO control loop dropped below +11 dBm.
3. DS2: The second fault the IF Lock Fault, indicates that the VCO phase lock is at a low or fault level, indicating the VCO is unlocked.
4. DS4: The third fault indicates that the Multiplier A8 CCA output has level has dropped 6dB or more.
5. DS1: The fourth fault indicates that a Reference Lock fault has occurred. This fault will be activated if any of these two conditions occur; a fault or unlock condition has occurred in the Reference Transmit Loop or the reference lock if the divided 10 MHz signal is compared to the 10 MHz RB Standard and an error signal is detected and the Phase Lock Detector is out of phase lock. DS1, the Transmit Summary Fault LED on the front panel is also on.
6. The fifth error is the Transmit Error. This error is initiated if the thumbwheel switch is broken or in between switch selections. This fault is the only fault that won’t light a fault light on the A7 CCA. But, it will light DS1 Transmit Summary Fault LED on the front panel.

7. Receive Loop BITE Circuitry Block Diagram
Now lets take a look at the Receive Loop BITE Circuitry and discuss the conditions that causes these BITE LEDs to activate. Refer to FO 12-1 above.
1. There are five faults that will cause the RX Summary LED DS2 to activate on the front panel. These five conditions are listed below. The A7 CCA contains internal fault LED indications for the Receive Loop.
2. DS6: The first fault indicates that the power out of the VCO control loop dropped below +11 dBm +/- 2 dB.
3. DS3: The second fault the IF Lock Fault, indicates that the VCO phase lock is at a low or fault level, indicating the VCO is unlocked.
4. DS4: The third fault indicates that the Multiplier A8 CCA output has level has dropped 6dB or more.
5. DS1: The fourth fault indicates that a Reference Lock fault has occurred. This fault will be activated if any of these two conditions occur; a fault or unlock condition has occurred in the Reference Receive Loop or the reference lock if the divided 10 MHz signal is compared to the 10 MHz RB Standard and an error signal is detected and the Phase Lock Detector is out of phase lock. DS2, the Receive Summary Fault LED on the front panel is also on.
6. The fifth error is the Receive Error. This error is initiated if the thumbwheel switch is broken or in between switch selections. This fault is the only fault that won’t light a fault light on the A7 CCA. But, it will light DS2 Receive Summary Fault LED on the front panel.

8. Controls and Indicators
Now lets discuss the front panel of the Dual Frequency Synthesizer.
1) TRANSMIT-TUNE- meter and control - Green segment indicates when internal voltage controlled oscillator is phase locked. Control tunes the transmit VCO (Knob has locked and unlocked position).
2) TRANSMIT SUMMARY FAULT -(red) LED- Indicates a fault in the transmit circuitry or incorrect tuning.
3) TRANSMIT FREQUENCY-TUNE – five digit thumb wheel switch - Set for desired transmit frequency.
4) RECEIVE FREQUENCY-TUNE - five digit thumb wheel switch - Set for desired receive frequency.
5) RECEIVE SUMMARY FAULT -red LED- Indicates a fault in the receive circuitry or incorrect tuning.
6) RECEIVE-TUNE - meter and control- Green segment indicates when internal voltage controlled oscillator is phase locked. Control tunes the receive VCO (Knob has locked and unlocked position).

9. Component Location
Now lets take a look at the component location of the circuit cards and modules that make up the Dual Frequency Synthesizer, the SN-553. Explain what circuit cards and modules are interchangeable.
1. Component Location:
A1: Cavity Tuned Oscillator (VCO)
A2: Cavity Tuned Oscillator (VCO)
A3: RF Converter Module
A4: RF Converter Module
A5: Intermediate Frequency (IF) CCA
A6: Intermediate Frequency (IF) CCA
A7: Reference and BITE CCA
A8: Multiplier Module
A9: 100 MHz Reference Oscillator Module
2. The following items are interchangeable
A1: Cavity, Tuned Oscillator with A2: Cavity, Tuned Oscillator
A3: RF Converter Module with A4: RF Converter Module
A5: IF Circuit Card Assembly with A6:IF Circuit Card Assembly

10. Rear Panel
Lets discuss the rear view connections of the Dual Frequency Synthesizer SN-553.
Connector Jack Nomenclature
J Power DC Voltages Input
J Dual Synthesizer Fault Alarms Output
J Transmit Local Oscillator 4.47 to 5.07 GHz
to Up Converter Output
J MHz Reference Input
J Receive Local Oscillator 4.47 to 5.07 GHz
to Dummy Load Output
J Receive Local Oscillator 4.47 to 5.07 GHz to
D/C #1 and to D/C # 3 Output
J Receive Local Oscillator 4.47 to 5.07 GHz to
D/C #2 and D/C # 4 only used in the V2 Output
GND Ground Connection

11. A7 BITE LED Fault Conditions
Synthesizer A7 CCA BITE LED Indications per Fault Conditions
Table 12-1 Synthesizer A7 BITE Lamp (LED) display per fault conditions.
LED INDICATION INTERNAL FAULT CONDITION
DS1 The Reference Lock is used by both transmit and receive BITE to indicate a malfunction of the reference loop.
DS2 Transmit IF Lock Fault – If the VCO phase lock is at a low or fault level, indicating the VCO is unlocked.
DS3 Receive IF Lock Fault – If the VCO phase lock is at a low or fault level, indicating the VCO is unlocked.
DS4 Multiplier Fault – monitors for a 6 dB loss of the 4.6 and 4.8 GHz signals.
DS5 Transmit VCO Power Out Fault – activates if the power level drops below +11 dBm.
DS6 Receive VCO Power Out Fault – activates if the power level drops below +11 dBm.
Reference page in handbook.

12. Synthesizer Transmit Summary Fault Conditions
Table 11-2 Synthesizer Transmit Summary (LED) display per fault conditions.
Transmit Summary LED DS1 on the front panel will activate when any of these five conditions occur.
1. DS5 LED on the A7 CCA is activated when the Control Loop drops below +11 dBm.
2. DS2 LED on the A7 CCA is activated when VCO phase lock is at a low or fault level indicating the VCO is unlocked.
3. DS4 LED on the A7 CCA is activated when either multiplier output level drops 6 dB or more.
4. DS1 LED on the A7 CCA is activated by a Transmit Reference Lock fault.
5. Transmit Error is initiated if the thumbwheel switch is broken or in between switch selections.
This fault won’t light a fault LED on the A7 CCA.
Reference page in handbook.

13. Synthesizer Receive Summary Fault conditions
Table 11-2 Synthesizer Receive Summary (LED) display per fault conditions.
Receive Summary LED DS2 on the front panel will activate when any of these five conditions occur.
1. DS6 LED on the A7 CCA is activated when the Control Loop drops below +11 dBm.
2. DS3 LED on the A7 CCA is activated when VCO phase lock is at a low or fault level indicating the VCO is unlocked.
3. DS4 LED on the A7 CCA is activated when either multiplier output level drops 6 dB or more.
4. DS1 LED on the A7 CCA is activated by a Receive Reference Lock fault.
5. Receive Error is initiated if the thumbwheel switch is broken or in between switch selections.
This fault won’t light a fault LED on the A7 CCA.
Reference page in handbook.

14. Troubleshooting (DS1) Reference CCA Out of Lock
Back
(DS1) Reference CCA Out of Lock
(DS3) Receive IF CCA out of Lock
(DS6) Receive Power Out LOW
(DS5) Transmit Power Out LOW
(DS2) Transmit IF CCA Out of Phase Lock
(DS4) Multiplier Failure
Front
Reference page in handbook.

15. Summary
Provides the Local Oscillator Frequency for the Up and Down Converters
Easy to troubleshoot using the BITE.
Recap slide.
Q: What is the purpose of the Dual Synthesizer?
A. Provides the Local Oscillator Frequency of 4.47 to 5.07 GHz for the Up and Down Converters.
Q: What two faults won’t activate any fault lights on the A7 CCA?
A. The Transmit and Receive Error. These errors are initiated if the transmit or receive thumbwheel switch is broken or between switch selections.
Q: If 4.4 GHz is set on the transmit front panel thumbwheel switch, then the output of the Cavity Tuned Oscillator A1 is?
A GHz, the output of the Cavity Tuned Oscillator is always 70 MHz above the desired operating frequency.
Q: What signal is called the base frequency and what unit provides the Synthesizer with this important input signal.
A. The 10 MHz signal from the Transmit Tropo Modem (RB Standard).

16. THIS PAGE LEFT BLANK