Single Side Band (SSB) Signal Adjustment


Follow these steps to remove high order inter-modulation distortion.



Step 1

Connect the transmitter to a dummy load

 

Step 2

Identify the MIC GAIN control.

This is before the clipper stage (see above).

Step 3

Identify the processor ON/OFF button, and the PROCESSING level control.

The PROCESSOR level control is inside the clipper stage (see above).

Step 4

Identify the RF POWER control (often called PWR).

This comes after the clipper stage. It controls the level of the clipped signal, and the drive to the POWER AMPLIFIER (PA).

Step 5

Set your transceiver to full power, and adjust the PA as normal.

 

Step 6

Set your transceiver to SSB, and the processor button to OFF. Adjust the MIC level control according to your radios manual. 

Set the MIC control so that the ALC meter is just below maximum during speech peaks.

Step 7

Turn the PROCESSING control fully clockwise (maximum), and the processor button to ON.

Give a long, loud "Haaaaaaaaalo" into the microphone.  Adjust the RF POWER level for maximum output from the PA. 

Be sure to do this into the dummy load only!  Do not whistle, it is too high pitched to give full output.  At this stage you will be generating horrendous splatter!

Step 8

Back off the RF POWER control until the output from the PA drops by about 10%.

Note the setting of the RF POWER control, and then don't touch it again. This is the step that will give you a clean signal.

With most transmitters, reducing the peak power by about 10% from the maximum possible (saturated) level makes a huge improvement in IMD levels. Reduce your drive power to the level where the RF output starts to drop off quickly - about 10% usually does it.

Step 9

Listen to your signal on another receiver. Turn the PROCESSING level control fully counter-clockwise.  Advance it slowly until your voice sounds loud and crisp, but not distorted.

If the background noise in your shack is noticeable, you will have to back off the PROCESSING control. Important: during this step, do not touch the RF POWER control!

Step 10

Ask a local station for an SSB quality report, with and without processing. If your signal is broader with the processor on, turn down the RF POWER control until it is narrower than before.

Your signal should be narrower with the processor on than without it - because the processor should be preventing those peaks of overdrive.

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