1. CECOM LAR Operation Course
LINK ESTABLISHMENT
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
WHAT IS A LINK?
TRANSMISSION LINK (AKA “SHOT”)
ESTABLISHED WHEN TROPO MODEMS ARE LOCKED UP WITH 10-5 BER SHORT
THIS HAS NOTHING TO DO WITH USER DATA—TROPO MODEM BER IS FROM DISTANT END TM FRAME PULSES
DGM EQUIPMENT DOES NOT HAVE TO BE ON TO ESTABLISH TRANSMISSION LINK
DATA LINK
ESTABLISHED WHEN DGM EQUIPMENT IS GREENED UP
TEDS (IF USED) ARE FULL OP/RESYNC
USERS ARE PASSING DATA TRAFFIC
Cover above points. Emphasize that getting the shot in has nothing to do with user data.
If red lights bother you, turn off the DGM rack until you get the shot in—10-5 BER on TM.
Signal Flow

3. CECOM LAR Operation Course
PROCEDURE
Set up the system, carefully orienting antenna positions to correct cutsheet azimuth.
Configure the system per the cut sheet. Make all presets: tune Synthesizer(s), Upconverter(s), Klystron(s), and set up Tropo Modem. Perform IF Loopback, if desired.
Prior to connecting wave guides, perform Gain Equalization procedure.
Loopback your users, if they are up at this time. (They usually will not be).
Bring up the transmit and establish the transmission link. Note that DGM equipment does not have to be turned on at this time. If it is, ignore red lights until the transmission link is in.
Generally, you shouldn’t start worrying about data link (users) until you get the shot in.
Remember, If you don’t have a Tropo Modem BER of at least 10 neg 1.5 or 2, the Tropo Modem sends out a Frame Search suppress signal to the DGM that keeps it from even looking for their framing bits. So they will always have red lights until the TM frames up.
Signal Flow

4. CECOM LAR Operation Course
PROCEDURE (CONT.)
6. Contact Distant End by orderwire. Coordinate antenna alignment procedure.
7. Orient the Antennas at both ends, using the RAAM.
8. Test Transmission Link Quality. Should have 10 neg 5 BER Short at designated data rate.
9. Troubleshoot as Required.
10. Turn on DGM equipment, patch and program DGM per cut sheet, if someone hasn't already done this while the shot was being worked in.
Cover slide.
Signal Flow

5. CECOM LAR Operation Course
PROCEDURE (CONT.)
11. Loopback all users, put loopbacks on your GM ports, and get your DGM to green up with distant end. Troubleshoot as required--See Loopbacks chapter.
12. Patch and Load COMSEC.
13. Normalize User Interfaces. Loop back those that are not up yet. At this time the DGM should be green at both ends. Troubleshoot as required.
14. Check your users and establish local orderwire.
15. Turn the link over to users. Monitor system till ENDEX.
Cover slide.
Signal Flow

6. CECOM LAR Operation Course
System Setup
·    Tune the HPA FL2 Output Bandpass Filter (Tropo and LOS)
·    Tune the Klystron(s) (Tropo)
·    Tune the Downconverter(s) (Receivers)
·    Tune the Upconverter(s)_
·    Turn on power breakers and switches (do not energize Beam Voltage)
·     Put the HPA(s) in LOS and Dummy Load
    
Don’t forget that FL2 must be tuned whether in LOS or TROPO mode.
Don’t forget the rules for tuning the Klystron.
Signal Flow

7. CECOM LAR Operation Course
System Setup (cont)
·    Insure the waveguides are not connected and waveguide port covers are installed
·    Set up the Tropo Modem
·    Perform Gain Equalization
·    Perform Receiver Channel Pre and Post Noise Tests
·    Troubleshoot as required
If you have already hooked up the wave guides, which usually happens, you must tune the receive chain (synthesizer, Down Converters) to an unused frequency before performing the Gain Equalization. Remember, there must be nothing but receiver noise to do Gain Equalization.
As an alternative to retuning, you could crank the antennas to their upper limits to avoid any interfering signals.
QUESTION: What is the purpose of the Noise Test?
Signal Flow

8. Connect the Antennas Set Up Transmit · LOS-- · Tropo
o       Change from Dummy Load to Antenna
o       Check Output and Reflected Power
·        Tropo
o       Select Tropo Low or High as directed
o       Bring up HPA per Chapter 14

9. CECOM LAR Operation Course
Establish Contact w/ Distant End (Radio or Phone)
Perform Antenna Orientation Using RAAM
ALWAYS!
If your initial antenna setup was close enough, you might have a good enough signal to talk Orderwire right away.
But even if your shot “drops right in”, ALWAYS perform antenna orientation for best RSL on the RAAM. Use the RAAM expanded scale to easier see the signal level fluctuation.
Establish Distant End Orderwire Contact
Signal Flow

10. CECOM LAR Operation Course
Configuration
·        Set up the DGM equipment
·        Patch equipment, bypassing TED(s) if used
Loopback Users
·        Put all user groups in a bi-directional loopback
·   Check to see if users see loopbacks as appropriate
Remove User Loopbacks
System should remain “green”
Cover slide
Signal Flow

11. COMSEC
·   Patch COMSEC
·   Load COMSEC
·   Check COMSEC (Full Op, Resync, and Power lights on)
Note: Watch the Resync Light(s) carefully to insure they are not blinking rapidly
·   Users should see loopbacks
·   Troubleshoot as required till system is “green”
Establish Local Orderwire (if applicable)

12. CECOM LAR Operation Course
Test the Link
·  Without TMDE:
o    Evaluate RSL’s for Each Receiver
o    Check AGC Levels
o    Check Short BER
Check Long BER (2 cycles, 20 minutes minimum)
If you don’t have any TMDE, just check the RSL levels for each receiver—should be 35 to 40 or higher. A strong signal will be 50 to 60 on the Alarm Monitor meter.
The AGC levels will be mid scale or higher, and it it is a Tropo shot, will probably fluctuate.
BER Short will be 10 neg 5. After 10 minutes they should be 10 neg 7.
Signal Flow

13. CECOM LAR Operation Course
Test the Link
·    With TMDE:
o    Wait for Good Long BER
o     Connect SG-1139 (Both Sides of Link)
o     Evaluate Resulting BER Readings
Troubleshoot as Required
Turn Link Over To Users
If you have an SG-1139 (and you should), you can hook it up to a TGM port, if you have the right cables, or to LGM binding posts on the ouside, if you are using the LGM, have the distant end do the same, and see if the link is taking errors.
To calculate the BER, count the errors for a given time period and divide that by the number of bits transmitted during the same time. (Multiply the SG-1139 data rate by the number of seconds in the time period).
Usually you can tell if it’s a good link just by looking at the SG-1139 and seeing that it is running error free or taking very few errors.
Signal Flow