Radio Oceanography Laboratory Support | Production / Testing the Mark-III 8-channel complex receivers

The assembly of the Mark-III CRX-8 is vastly simplified, so it is included here for convenience.

All screws for mounting PCBs are #4-40 x 1/4 except for Analog Backplane (3/4")
Mount the Analog Backplane to the center of the baseplate.
Mount the LO Backplane on top of the Analog board with standoffs.
Plug in the eight complex receiver boards and screw them down.
Solder 24 inch black and red #16AWG wires to the bottom of the power supply board.
Mount the power supply board. Wire the power wires to the terminal strip on the LO backplane.
Assemble the enclosure.
Mount the completed baseplate.
Add eight SMA cables (18" SMA to SMA RA) to the eight receivers.
Add two SMA cables (25" SMA to SMA RA) to the LO I and Q.
Wire the power supply input to the power plug and switch.
Clamp ferrite noise suppressors around power cables and secure with adhesive pad at each end.
- loop the excess wire through the back suppressor.
Route the power LED fiber optic to the front panel.
- DONE

Fig. 1.1.

Trouble shooting phase

Fig. 2.1 Note that on the Gain Boost jumper on Q, the A and B labels are backwards. The Q (lower) jumper should be on B.

To quickly identify a broad range of initial problems, the VNA-2180 works very nicely. It provides a broadband sweep of the channels and quickly detects variations in gain and a wide range of other problems.

Fig. 2.2.

Place a 20dB attenuator with a SMA adapter on Port A for the signal. Use the 3-pin header to SMA test probe cable adapted to Port B.
Run VNA2180 calibration with the 40 dB attenuators in place, ignoring the error message.
Run Scan B on each of the RF test points in Figure 4.

Fig. 2.3.

Individual troubleshooting will be required for any channels that deviate from the plots below before final testing can begin.

Fig. 5. Normal plots. (Use [Rescan B] to superimpose the RF signals just before the mixers.)
Note the almost trivial phase differences between the LNA and the two RF signals.

Fig. 2.4. Example of anomaly. Remove L104 and replace with a zero ohm jumper.

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For final testing, you will need a LERA DDS signal generator for standard signals.

The TX output has a step attenuator for fine tuning the amplitude. Additional attenuators may be needed.
A 1000ft spool of RG-174 cable provides both attenuation and "direct path" delay.
The test is run at 16 MHz. Use the "Calibrate" mode with 80Hz offset.
Use the Analog Breakout Board to access the analog signals to channels 1 and 2 of Tektronics Scope.
Make sure the Analog Gain jumper is properly set.
Adjust the RF step attenuator to get 3 to 10 volts peak-to-peak analog signals.

This step verifies that the entire RF, LO and Analog signal chain is at least functional.

Record the analog signal levels for all eight I and Q outputs: (No need to record the Mixer outputs.)
If the output is dead, you can immediately see if the signal is getting as far as the mixers. If the output amplitude is wrong, this verifies the gain jumper settings.

Component: I,Q
Channel 1: __._______v __.________v
Channel 2: __._______v __.________v
Channel 3: __._______v __.________v
Channel 4: __._______v __.________v
Channel 5: __._______v __.________v
Channel 6: __._______v __.________v
Channel 7: __._______v __.________v
Channel 8: __._______v __.________v

Fig. 3.1. Analog Signals. The top two traces are the mixer output test points (Mixer-I and Mixer-Q). The bottom traces are from the Analog Breakout Board.

For a final test, while observing the analog signals on the scope, lift the front of the chassis 2 inches and drop it onto the table. This is an extreme shock test to detect cold solder joints, etc. There should be no glitches in the signal whatsoever. By lifting at the front, you are pivoting at the rear panel, so minimal stress is placed on connectors. This should be done once for each channel pair while testing above.

If any glitches are seen, the green "suction cup" massager can effectively provide continuous vibration to track down the problem.

In still ambient air, the ait inside of the upper enclosure reaches an equilibrium temperature around 40 degC. The lower portion is around 30 degC.

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