AL-80B Instruction Manual
22
Additional SSB Notes
The peak power output developed on SSB is limited by the amplifier loading, RF drive, and peak-
to-average power of the RF waveform. Proper loading of this amplifier will produce excellent
linearity and a clean signal even if the output power level exceeds one kilowatt PEP. An improperly
adjusted (too far counter-clockwise) "LOAD" adjustment can produce flat-topping and splatter with
only a few hundred watts of RF output. The "LOAD" setting is the single most important adjustment
for proper SSB operation.
Note:
The "LOAD" control setting is the most important adjustment for good linearity!
To maintain linearity, always be sure that the "LOAD" control is adjusted far enough clockwise for
the peak drive that will be applied.
Be considerate of others, NEVER "push" this amplifier into envelope clipping or to the point where
the grid current approaches 75 mA on voice peaks. Envelope clipping can be also be avoided by
adjusting the amplifier's "ALC SET" control until the peak output power drops slightly from the
power obtained with full microphone gain and a fully clockwise "ALC SET" adjustment. For the
cleanest audio, the microphone gain can be reduced until the ALC meter just flickers.
AM (Amplitude Modulation) Operation
The efficiency of any conventional linear amplifier must remain below half the peak efficiency
under maximum signal conditions (less a safety factor) in AM operation. Since this linear amplifier
has a peak plate efficiency of nearly 65%, the carrier efficiency must be kept below 30% to maintain
linearity. The power dissipated in the tube anodes will be more than twice the carrier output power.
The carrier power must be kept below 200 watts for clean and safe AM operation. With 200 watts of
carrier, the peak envelope power will reach 800 watts with 100% symmetrical modulation. The
modulated AM power output should be limited to 1000 watts peak with non-symmetrical
modulation that enhances the positive peaks.
FM (Frequency Modulation), RTTY, and Digital Operation
The efficiency of this amplifier will approach 65% in the FM, RTTY and Digital Operation modes.
Since these modes do not require linear amplification of complex waveforms, the tuning can be re-
adjusted for maximum power at the desired output power level. This will keep the efficiency as high
as possible.
Audio Distortion
One problem that often occurs when using a linear power amplifier is SSB audio distortion on one
or more bands. This distortion is usually caused by RF feedback from either a poorly designed
antenna or poor RF grounding. REMEMBER THAT A GOOD GROUND FOR DC IS NOT
NECESSARILY GOOD FOR RF. RF circuits require short connections with smooth, wide
conductors. Braiding or woven wire has a very high RF resistance and should be avoided. See the
"Grounding" section on page 11 of this manual. More detailed suggestions on grounding are
available by requesting Ameritron's Tech Bulletin on RF Feedback.
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