1. CECOM LAR Operation Course
IF TEST PANEL
CECOM LAR Course
Logistics Assistance Division
Fort Monmouth, New Jersey
The IF TEST PANEL is a major test and troubleshooting tool. This class covers the IF TEST PANEL.
Signal Flow

2. CECOM LAR Operation Course
Here’s where it is in the system
Point out it’s relationship to Tropo Modem Transmit and Demod sections and the D/C’s
Three purposes:
Provides a loopback capability for a sample of the Tropo Modem transmit signal.
Provides a pass through for the four V2 receive signals. In the V3 there is a power splitter that splits the two receive signals into four to send to the four Tropo Modem Demodulator channels.
Although not shown here, it also looks at the signal level from each D/C and provides an RSL voltage to the Alarm Monitor RSL meter.
Also not shown here is the mounting panel between the D/C’s and the IFTP. The cables actually run from each D/C to the panel just above the IFTP, and then from there down to the IFTP.
Signal Flow

3. CECOM LAR Operation Course
LOCATION V3
TED 1
KG-194
TED 2
KG-194
BASEBAND PATCH PANEL
BLANK
FOR DELED
BLANK
FOR DELED
DELED PATCH PANEL
LGM
TD-1235
ALARM MONITOR
BZ-250/TRC-170
Analogue Voice Order Wire GM
MD-1026
TEST PANEL I.F.
ORDER WIRE CONTROL UNIT
OCU C-10602/TRC-170
TGM
TD-1236
AC-AC CONVERTER
HERE’S WHERE IT’S LOCATED:
Show where the IFTP is in the V3.
Note the physical location in relation to the Down Converters—note that cables must physically run across the van from the D/C to the A5A3 Blank Panel, then down to the IFTP at A5A6.
Then from the IFTP, back across the van to the TM Demod section.
These cables sometimes get damaged or broken, so this cable path needs to be understood, because you will often be troubleshooting bad cables. The first indication of a bad cable is when the Tropo Modem will not gain equalize on one or more channels. Although there are several other more likely suspects for this problem, bad cables are always a good possibility
LGM
TD-1235
POWER SUPPLY PP-7904/TRC-170
Key to lab
AN/TRC-170 V3 CURB SIDE
Signal Flow

4. CECOM LAR Operation Course
LOCATION, V2
In the V2, the IFTP IS LOCATED IS LOCATED AT 7A5
The cable runs are from the D/C’s in rack 4, over to blank mounting above 7A5, and then to the IFTP at 7A5.
Signal Flow

5. CECOM LAR Operation Course
IF TEST PANEL C & I
The TEST SIGNAL jack brings out the TM transmit signal sample so we can look at it on a Spectrum Analyzer, Oscilloscope, or measure it with a power meter (-23 dBm).
Then it goes to the attenuators for level control. This allows you to simulate a received signal by decreasing the level being sent to the TM demodulator in loopback.
From the attenuators it goes to the loopback switches which pass the test signal (along with any signal that happen to be coming in from the D/C’s) over to the Tropo Modem Demodulator.
Signal Flow

6. CECOM LAR Operation Course
IF TEST PANEL REAR VIEW
This is rear view of a (V)3 IFTP. Note J16 and J17, which accept the D/C inputs and direct them into two power splitters, which develop the four signals to send to the Tropo Modem Demodulator section.
If it were a (V)2, J16 and J17 would be empty and J12-J15 would be active.
In either case, J11 is input for the tropo modem transmit test signal, and J6-J9 are outputs to the Tropo Modem Demodulator section.
Signal Flow

7. CECOM LAR Operation Course
DC1
Directional Coupler
D/C 1
D/C 2
D/C 3
D/C 4
70 MHz
RCVR 1 IF (70 MHz)
J12
RCVR 2 IF (70 MHz) J9
70 MHz
RCVR 1
Norm To
Tropo
MODEM
Receivers
RSL-1 J6
J15 LB
RCVR 3 IF (70 MHz)
70 MHz J7
J14
RCVR 4 IF (70 MHz)
70 MHz
DC 2
Directional Coupler J8
J13
RCVR 2
Norm LB
RSL-2
DC 3
Directional Coupler
RCVR 3
Norm LB
RSL-3
DC 4
Directional Coupler A6
Power
Splitter
FL 2
50 KHz
Filter
RCVR 4
Norm LB
RSL-4
TEST SIGNAL LEVEL
AT2
Step Attenuator
FL 1
5 MHz
Filter
10 DB
1 DB
Transmit
70 MHz
From
Tropo
Modem
J11
Red
RSL-1 1
Antenna 1
Red
Cover the three functions of the IFTP as shown in the block diagram.
Receive signal pass through—from J12-15 , which come from the D/C by way of the blank mounting panel just above the IFTP, through the Directional Couplers (DC), to J6-J9 out to the Tropo Modem Demodulator section.
The loopback function, which takes the transmit sample in through J11, through the attenuator, up to the loopback switches, which apply the test signal through the DC’s onto the receive signal path, which goes to the Tropo Modem Demodulator section.
The RSL function, which takes a sample of each receive signal, and applies it to a selector switch that is physically located on the Alarm Monitor Panel. This selected sample is then returned to the IFTP and run through a circuit that provides a dc voltage back up to the meter on the Alarm Monitor Panel. This voltage is proportional to the receive signal level, and is displayed on the meter as RSL.
MAJOR POINT: When in loopback, the receive signal is still connected. So make sure you aren’t receiving a signal, because it will degrade the BER reading on the Tropo Modem meter.
RSL-4 4
RSL
Voltage
Out A1
Amplifier K8
Bandwidth
Select A2
Log Amp
TEST
SIGNAL
Black To
Alarm
Monitor
70 MHz
RSL-3 3
Antenna 2
Black
J4-D
RSL-2 2
Note: RSL & Antenna switches are
physically located in the Alarm
Monitor
From
Alarm
Monitor
Bandwidth Select
J4-G
IF Test Panel (V2 Only)
Signal Flow

8. CECOM LAR Operation Course
At any time when the van is powered up, the IFTP can be placed in loopback with any one or all of the loopback switches, and if the Tropo Modem is operational, DEMUX FRAME light should go out immediately, and the BER SHORT should go to 10 neg 5 BER within 60 seconds, assuming the following conditions are met:
1. IFTP front panel attenuators set to zero.
2. CW/NORM switch set to NORM.
3. MISSION data rate set above 64 Kb.
4. Bandwidth switch set to 7.5 if MISSION data rate set above 2304 Kb.
5. No interfering signal being received through the antenna ports
Note that the DGM equipment does not even have to be turned on for the above to happen.
Signal Flow

9. AN/TRC-170(V)3 Receive 70 MHz (IF) Signal Flow

10. CECOM LAR Operation Course
SUMMARY
TOOL FOR SYSTEM CHECKOUT
TOOL FOR TROUBLESHOOTING
PROVIDES RSL TO ALARM MONITOR
PROVIDES SAMPLE TRANSMIT OUTPUT AT FRONT PANEL
PRONE TO CABLE FAILURES
Cover above notes.
Signal Flow

11. QUESTIONS FOR YOU What is center freq of TEST SIG out at front panel?
What is purpose of front panel attenuators?
What position should TM BER switch be in when checking IF Loopback?
Where do you select the D/C whose RSL you want to check?
On an FTX you’re getting poor BER. You go to loopback and the BER doesn’t come up. Why?