• Print
• .

LERA DDS Quality control

Not tested: CLK output voltage (use oscilloscope). Should be a square wave at 12.5 MHz of 2.7 V on 50 Ohm load. If instead it is 800 mV on 50 Ohm load, please open DDS and return board clkbuf06.pcb to Hawaii for exchange against a replacement board that has the correct voltage.

Serial DDS-1-03 (Mexico)

• VECTRON serial number: 2154246-0003 (24.8 MHz)
• Novatech primary serial: 27
• Novatech secondary serial: 28
• LO-BUF board: 03
• LO-DIST board: 03
• power supply board: 03

1. Checklist

• DC input ferrite (tied down): V
• fan shroud (glued down): V
• 700 Ohm piggy-backed R26 on Q channel: V
• clock grounding strap: V
• USB FTDI grounding strap: V
• VGA board clears LO-DIST board: V
• IQ cables from DDS-1 to LO-DIST same length: V
• adjust auxilary heater to minimum (CW): V
• heatsink clued to each DDS: V
• thermal foam under and in front of clock bell: V
• solid contacts at crimped connectors: V
• heat shrink at 12 V splitter: V
• tape marking 12 V and 5 V on cables to LO-DIST and LO-BUF boards: V
• relay control connected to BNC: V
• front panel fiber optics blink: V
• fan and velcro, tied down at (11,11.5) cm: V
• jumpers
  • serial enable, DDS1 and DDS2 boards: VV
  • external clock, DDS1 and DDS2 boards: VV
  • VCO disable, CLK board: V
  • external clock, LO-BUF board: V
  • triple, 2/22 dBm TX output, on 22 dBm, glued, LO-DIST board: V
  • TUF source internal, LO-DIST board: V
  • 0-Ohm resistance on divide by 2, LO-BUF board: V

2. Power supply measurements

(use EDAC 10953A 12 V 80 W adapter only)

• DC voltage 12 V input: 12.12 V
• DC voltage 5V PSU output (V): 4.85 V
• DC voltage -5V PSU output (V): -4.79 V
• DC current reading (A): 1.66 A (clock warmed up, chirping)
• AC power reading (A): 23.2 W
• temperature brass bell/air: 40/23 C

3. Program DDS

Connect USB to linux, check that /dev/ttyUSB{0,1,2,3} appear, open screen to each of them and check red/green LED blink on FTDI board. Verified: VVVV

For production, the Vectron clock is used /4 at 25 MHz, and the LO-BUF board is used to distribute the clock to the DDS boards. DO NOT connect the 50 MHz output of the Vectron directly to the DDS, as there may be issues with the correct KP setting at boot time.

Primary and secondary DDS, reset to factory default and clear parameter memory:

 CLR
 S

Power cycle and check with frequency meter that they both output 8.8817842 MHz, the default of 10 MHz scaled by the clock ration. Then, proceed with programming.

Primary DDS, record commands:

 F1 15.645313160533
 Fd 0.000000002218
 Td 1
 Tr 52428799
 M 3
 A D
 VQ 3600
 VI 3600
 S

QUE string:

 000000000E3AB55555550000000000000000000008AA031FFFFF000001004A87400FFF0FFF000FFF

Secondary DDS, record commands:

 F0 15.645220102908
 M 0
 S 

QUE string:

 000000000E3AAFC962FC00000000000000000000000000000005000000004A00400FFF0FFF000FFF

4. Signals measurements and adjustments

Frequency meter:

Clock: temporarily set jumper to VCO on, using Rb external clock and frequency counter, set back to VCO off after tuning

• adjust VCO to 50.000000 MHz: V
• check auxiliary DDS1 and DDS2 clock output 25 MHz: VV
• check Trig chirp length to match programmed DDS1: 2.3841857 Hz
• check D-Tacq clock output 12.5 MHz: V
• check bandwidth on spectrum analyzer: 100 kHz centered at 12.000 MHz OK

RF power meter: Mini Circuits PWR-SEN-6G+ USB power sensor

Note: terminate all back panel open connectors with 50 Ohm while measuring

• probe on I1=I2, adjust DDS1 I channel so that output is -3 dBm
• probe on TX, adjust LO-DIST pot so that output is +18 dBm
• enable calib mode, adjust DDS2 so that output is +18 dBm
• probe on Q1=Q2, adjust DDS1 Q channel so that output is -3dBm, in software with VQ command:

 VQ 3670
 S

QUE string

 000000000E3AB55555550000000000000000000008AA031FFFFF000001104A87600E100E56000FFF

Oscilloscope on 1 MOhm input:

• Audio out adjust to max. gain CCW: 108 mVpp
• Trig, check SMA pulse: 4.40 Vpp 950 us

Disable clock VCO, power cycle and verify that it comes back with all the parameters OK: V

5. Spectrum Analyzer Images