Figure 128. Picture Of Simulated Opposite Sideband Rejection When Optimally Tuned Up - NORCAL NC2030 Manual

If you find that you cannot get much of a null, you are very likely listening to the lower side band signal
rather than the upper sideband signal. Tune the signal through zero beat to the other sideband and try
again.
Next adjust the balance pot to further null out the signal as much as possible. The balance pot setting
should not be moved very little from its center position.
Go back and forth between the phase and the balance adjustment several times to get the best possible
null for this center audio frequency. After a few passes, the null ought to be very sharp.
At this point, with the last two adjustment pots at their mid range setting, the overall rejection ought to
be at least 35 db and you should hear a very distinct difference between the desired LSB sideband and
the phase canceled USB sideband. However, we are not yet finished tuning up the USB image rejection.

Figure 128. Picture of simulated opposite sideband rejection when optimally tuned up.

Now, from this center frequency tune to a lower audio tone. On the low end, the audio starts to roll off
below 400 Hz, so sweep the receiver around this low tone area and find the audio peak. Now adjust the
low adjustment to null out the low frequency.
Now tune the audio tone to a high frequency audio tone in the audio pass band. Sweep the receiver
around this upper audio area to find the peak (i.e., the point were the rejection is the worst) and adjust
the high adjust pot to the maximize the null of this high end audio.
The tuning of the high and low frequency phasing adjustments interact with each other, and the best over
all rejection will be a compromise of the best low frequency and the best high frequency rejection. An
AC voltmeter connected to the audio jack can be used to measure the frequency response and will give
the best indication of the audio rejection across the bandpass. Keep in mind that the audio limiter kicks
in at ~0.3v pk-pk or 0.15v peak, or 0.1v RMS so you will not get an audio output larger than this.
Norcal NC2030 v5 12-18-05
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