1. AM-7026 Down Converter-Receiver
CECOM LAR Tropo Operation Course
AM-7026 Down Converter-Receiver
CECOM LAR Course
Logistics Assistance Division
Fort Monmouth, New Jersey
In this class we will discuss the AM-7026 Down Converter.
It is also referred to as the receiver.
Down Converter

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Purpose
To amplify selected frequencies in the 4.4 to 5.0 GHz range and convert them to the nominal 70 MHz IF frequency.
Recap purpose
Please note that the AN/TRC-170(V)2 system has four (4 ea.) Down Converters installed and the AN/TRC-170(V)3 system has two (2 ea.) Down Converters installed.
Down Converter

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Block Diagram
1. Antenna Input: a bolted waveguide feeds the D/C from the top of the down converter.
2. FL1: Adjustable Bandpass filter with 2 couplers. The second coupled signal is passed to CR1.
3. CR1: If a signal of +20 dBm (100 mV) is detected here. AR1- The Low Noise Amplifier provides dB of gain.
4. AR1: Low Noise Amplifier, has a 25 to 28 dB gain.
5. DC2: Directional Coupler (discussed in the next slide).
6. FL2: Adjustable Bandpass filter.
7. A1: Balanced mixer and preamplifier. Here the received signal is mixed with the L.O. from the frequency synthesizer and difference of the two frequencies is sent to an 8 dB amplifier.
8. A5 BITE: Monitors inputs from CR1 and AR1. If CR1 detects a fault it sends a signal, which turns on DS2 on the front panel and inhibits the Up Converter. If a fault is detected in AR1 the summary alarm DS1.
9. RF Switch S1: used for test purposes, and is controlled by Noise Test Switch S2.
10. Noise Test Switch S2: controls the noise test measurement signal injection for test purposes via RF Switch S1.
Down Converter

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RF and IF Signal Flow
Now lets take a look at the RF and IF Signal Flow of the Down Converter. Please refer to FO 4-1.
Follow the Signal Flow:
1. Bandpass Filter FL1: The receive SHF signal 4.4–5.0 GHz comes from the Waveguide Entry Panel via waveguide to Preselector Filter FL1. FL1’s purpose is to pass the locally assigned receive RF Frequency & attenuate all other frequencies outside of the bandwidth. FL1 has a bandwidth of 7 MHz. Manually tuned in 5 MHz increments. The output of FL1 is coupled to the Low Noise Amplifier (LNA) AR1.
2. Low Noise Amp (LNA) AR1:The Low Noise Amplifier (LNA) AR1 has a gain of 25 to 28 dB. The amplified received RF signal is coupled to DC2.
3. Directional Coupler DC2: Couples the amplified RF signal via cable to FL2. DC2 also is used to couple noise in during noise test measurements.
4. Bandpass Filter FL2: The RF signal is passed to FL2. This signal leaves FL2 and provides an input to the Balanced Mixer/PreAmp A1.
5. Balanced Mixer/Preamp A1: This RF signal 4.4–5.0 GHz is one of the two inputs to the A1. The second input is a Local Oscillator LO at 4.47–5.07 GHz from the Receive Synthesizer. The A1 module, takes the received RF signal and the LO signal and mixes them internally to produce a difference frequency of 70 MHz IF that is passed to the TROPO Receive Modem via the IF Test Panel.
Down Converter

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Noise Test-Preselect
Now lets take a look at the Noise Test Preselect Signal Flow. Refer to FO 4-1.
Follow the Signal Flow:
1. The external output of the Noise Source Generator enters the Down Converter via RF Switch S1.
2. RF Switch S1: Is used to switch or terminate the input from the Noise Source for test purposes. Controlled by the front panel Noise Test Switch S2. Currently in the Pre-Select position, and passes the Test Noise to the 20 dB Directional Coupler DC1 on Filter FL1.
3. Bandpass Pre-Select Filter FL1: FL1’s purpose is to pass the locally assigned receive RF Frequency and attenuate all other frequencies outside of the bandwidth. The Bandpass Filter FL1 front panel scale is made of a paper strip located behind the plexiglas. This paper strip is marked in 5 MHz increments from 4400 – 5000 MHz. STOP is written at each end of the strip. DO NOT ADJUST THE FILTER PAST THIS POINT!
4. Low Noise Amp AR1: Amplifies this signal and sends it to FL2.
5. Directional Coupler DC2: Couples the LNA output to bandpass Filter FL2.
6. Bandpass Post-Select Filter FL2: Passes the assigned frequency & attenuates all other frequencies. Output is sent to the A1 module.
7. Balanced Mixer/Preamp A1: Mixes the input from FL2 & the LO signal of GHz to produce a difference frequency of 70 MHz IF.
Down Converter

6. Noise Test-Postselect
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Noise Test-Postselect
Now lets take a look at the Noise Test Postselect Signal Flow. Refer to FO 4-1.
Follow the Signal Flow:
1. The external output of the Noise Source Generator enters the Down Converter via RF Switch S1.
2. RF Switch S1: Is used to switch or terminate the input from the Noise Source for test purposes. Controlled by the front panel Noise Test Switch S2, and in this position will cause a configuration Currently in the Pre-Select position, and passes the Test Noise to the 20 dB Directional Coupler DC1 on Filter FL1.
3. Directional Coupler DC2: Provides for a 20 dB noise injection input to the Postselect Filter FL2 when the Noise Test Switch S1 is set to the Postselect position.
4. Bandpass Post-Select Filter FL2: Passes the assigned frequency & attenuates all other frequencies. Output is sent to the A1 module.
5. Balanced Mixer/Preamp A1: Mixes the input from FL2 & the LO signal of GHz to produce a difference frequency of 70 MHz IF. The Pre-Amplifier circuitry within the A1 provides two functions to the 70 MHz IF signal. The first function is to amplify the 70 MHz signal and provide a gain of 8dB. Next the 70 MHz IF signal is applied to an impedance matching network of 75, to interface the 70 MHz IF signal with the rest of the receiver circuitry.
Down Converter

7. Input Overload-U/C Inhibit, LNA Fault & Configuration Alarm
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Input Overload-U/C Inhibit, LNA Fault & Configuration Alarm
Now lets take a look at the Input Overload and LNA faults, Up Converter Inhibit, and the Configuration Alarm Signal Flow and discuss the conditions that causes these BITE features to activate. Refer to FO 4-1.
Follow the Signal Flow:
1. CR1 RF Detector: Monitors the output sample provided by FL1 to determine if an input overload condition +20dBm (100mw) has occurred. If an overload condition occurs, then a logic zero is sent to the BITE CCA A5 and the Input Overload LED will light on the front panel. In order to alleviate damage to the Down Converters, A5 CCA provides a logic signal called an Up Converter Inhibit when a OVLD fault condition is detected by RF Detector CR1. This signal will shut down the Up Converter.
2. LNA AR1 fault: Indicates failure of a transistor within the LNA and will causes the Summary Fault LED to light on the front panel.
3. Noise Test Switch S2: In the OFF position, the D/C is configured for normal system operation. In the PRESEL position, the noise test measurement signal is injected into FL1 via coupler DC1. In the POSTSEL position, the noise test measurement signal is injected into the front end of FL2 via the 20dB port of coupler DC2. When the PRESEL or POSTSEL positions are selected, a Configuration alarm is reported to the Alarm Monitor unit.
4. BITE CCA A5: Provides fault status to the front panel LEDs, along with the Up Converter Inhibit & Configuration alarms to the Alarm Monitor Unit.
Down Converter

8. Controls and Indicators
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Controls and Indicators
Now lets discuss the Controls and Indicators of the Down Converter front panel. Please refer to slide # 8 above.
1. SUMMARY FAULT -(red) LED indicator -Indicates a failure of a transistor within the Low Noise Amplifier (AR1).
2. INPUT OVERLOAD -(red) LED indicator - Indicates a preamplifier-input signal of at least 100 mV has been detected. This overload generates the RF inhibit signals for the Up Converter.
3. FREQUENCY MHZ PRESELECTOR - Tunable band pass filter with a BW of 7 MHz in 5 MHz steps. Used to tune the input of the Low Noise Amplifier (LNA) to the desired receive frequency.
4. NOISE TEST - Three position rotary switch (S2) used to control relay switching of the noise generator input via an internal RF switch S1. Used primarily to test for the proper operation of the LNA, and can be used to test other Down Converter components. When the switch in the position of PRESEL or POSTEL a Configuration alarm is reported to the Alarm Monitor Unit.
5. FREQUENCY MHZ POSTSELECTOR - Tunable band pass filter with a BW of 7 MHz in 5 MHz steps. Tunable from 4.4 to 5 GHz. Used to tune the output of the Low Noise Amplifier (LNA) to the desired receive frequency.
Down Converter

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Component Location
Now lets discuss the Component Location for the Down Converter. Please refer to slide # 9 above.
FL1: Wave Guide Pre-Select band pass filter has a 7 MHz Bandwidth. Manually tunable in 5 MHz increments.
AR1: Low Noise Amplifier (LNA) has a 25 to 28dB gain.
FL2: Coaxial Post-Select band pass filter has a 7 MHz Bandwidth. Manually tunable in 5 MHz increments.
CR1: RF Detector monitors the output sample provided by FL1. If signal strength is 20dB (100 mw) or greater then sends a RF overload fault to the BITE CCA A5.
A1: Balanced Mixer/Pre Amplifier mixes the Local Oscillator frequency with the receive frequency to produce the 70 MHz IF signal.
S1: RF Switch used to switch or terminate the input from the external Noise Source Generator used for checking the Down Converter modules.
Down Converter

10. Down Converter AM-7026 Rear View
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Down Converter AM-7026 Rear View
Now lets discuss the Down Converter AM-7026 Rear View. Please refer to slide # 10 above.
Connector Jack Nomenclature
J Power DC Voltages Input
J Noise Source Input
J O MHz IF Output
J Local Oscillator (LO) Input
J U/C Inhibit, D/C - Configuration Alarm Output
GND Ground Connection
Down Converter

11. Noise Source Generator
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Noise Source Generator
Now lets discuss the the Noise Source Generator. Please refer to slide # 11 above.
NOISE SOURCE GENERATOR: The Noise Source Generator is a broadband noise source in the 4.4 to 5.0 GHz spectrum. The Noise Source Generator is mounted in the shelter. The Noise Source Generator is used to test the Down Converters. It receives (+ 28 vdc) from the Down Converter under test. The output of the Noise Source is injected into the Down Converter when the Noise Test Switch (S2) on the Down Converter is placed in either the PRESEL or POSTSEL position, and a Configuration alarm is reported to the Alarm Monitor unit. Is mounted in rack location (4A4) in the AN/TRC-170(V)2, and mounted in rack location (3A4) in the AN/TRC-170(V)3 system.
Connector Jack Nomenclature
J Power DC Voltage (+28 vdc) from D/C Input
J Test Noise to D/C #3 Output
J Test Noise to D/C #1 Output
J Test Noise to Mounting Panel Output
J Test Noise to D/C #4 Output * Only used in V2
J Test Noise to D/C #2 Output * Only used in V2
J Test Noise to Mounting Panel Output * Only used in V2
Down Converter

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Summary
Purpose
Frequency range
Overload
Noise Test
Q: What is the purpose of the Down Converter?
A: Takes a selected frequency from 4.4 to 5.0 GHz, amplifies and converts it to a nominal 70 MHz frequency.
Q: What is the input frequency range of the Down Converter?
A: 4.4 to 5.0 GHz
Q: What is the output Frequency range?
A: 70 MHz
Q: What does the overload light indicate?
A: A signal of 100 mV (+20 dBm) has been detected by CR1.
Q: What effect does the overload cause?
A: It attenuates the output of the Up Converter.
Q: What is the purpose of the Noise Test?
A: To check the operation of the LNA.
Down Converter