Facilities

Using Frequency Converters with TWISTER

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Terms:

CCU:  Compact Up-Converter  (VDI-737 CC)

CCD:  Compact Down-Converter  (VDI-737 CC)

AWG:  M8195A - Arbitrary Waveform Generator

PSG:  E8257D - Analog Signal Generator (x2)

DSO:  DSOV254A - Digital Storage Oscilloscope

Important notes about operating the frequency converters:

• Wear a grounding strap when handling. The IF input of the CCU unit (and the rest of the devices to a lesser extent) are extremely ESD sensitive.

• Disable AWG and PSG outputs before connecting to input of CCU/CCD. Applying input signal to the devices in the wrong order or while they are powered off can result in irreparable damage.

Tips on calculating appropriate power output values

• See the datasheet for the particular CCU/CCD units you are using. The maximum
  allowable input power value varies by device. The limit also differs for the LO and IF
  ports.
• Remember to account for loss caused by the cables you are using. This should be listed
  on the cable spec-sheet, or it can be easily measured using the VNA or DSO.
• The cable loss varies by frequency. Make sure you calculate the correct loss for the
  frequency a particular cable will see.
• To calculate correct signal amplitude for the AWG, remember to convert AWG output
  voltage to RMS. The following formula can be used:
   
• Make sure you do not overload the RF input of the CCD (this isn’t likely to be a concern
  if the THz signal is not being amplified).

Startup Procedure

Start with all cables disconnected.

1. Calculate desired frequency/power output for PSG.
     -   see Tips on calculating appropriate power output values.
2. Set PSG output frequency and amplitude using the appropriately labeled buttons.
3. Disable the outputs of the PSGs.
   
   • The outputs should be disabled by default, but you should double check that the icon on screen says 'RF OFF'
     
     
   
   
   
4. Calculate and set desired output voltage for AWG.
     -   see Tips on calculating appropriate power output values.
     -  Tip: set maximum amplitude in Output tab and then adjust output level by changing FIR Scale value in the FIR Filter tab.
   
   
   
   
5. Disable the outputs of the AWG (uncheck ‘Enabled’ for each available channel in the
   Output tab). The channel LEDs should be unlit.
   
   
   
   
   
6. Double check that the outputs for each device are disabled.
     -  When in doubt, shut the signal sources off. Once you have made all the connections,
        they should boot up in a safe state.
7. Make sure the CCU/CCD are powered off (unplugged).
8. Connect Devices (see document on Proper use of high frequency coaxial cables)
     a.  PSG output to CCU/CCD LO inputs.
     b.  AWG output to CCU IF input.
     c.  CCD IF output to DSO input.Connect power to the CCU/CCD.
9. Connect power to the CCU/CCD.
10. Verify that PSG and AWG output levels are within the safe operating range that you calculated.
    
11. Enable PSG outputs.
12. Enable AWG outputs.

Shutdown Procedure

It is important that you turn off and disconnect devices in the correct order to avoid damaging equipment.

1. Disable AWG output.
2. Disable PSG output.
3. Disconnect CCU/CCD power supplies.
4. Power off AWG, PSG, DSO.
5. Replace the dust covers and/or protective tape on the CCU and CCD outputs.
6. Disconnect cables if system is to be stored.