AMERITRON AL-572 Bedienerhandbuch PDF herunterladen (Seite 28)

Ameritron AL-572 Instruction Manual

DDITIONAL

SSB N

OTES

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: Always remember that the "LOAD" control setting is much more important than

any other parameter for good linearity! Good linearity means a "clean" signal!

To maintain linearity,

always

be sure that the "LOAD" control is adjusted slightly further

clockwise

than the position that gives maximum output at

peak

or maximum drive.

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 (A

MPLITUDE

ODULATION

) O

PERATION

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 60%, the carrier efficiency must be kept below

30% to maintain linearity. The power dissipated in the tube anodes will slightly more than twice

the carrier output power.

The carrier power must be kept below 250 watts for clean and safe AM operation. With 250

watts of carrier, the peak envelope power will reach 1000 watts with 100% symmetrical

modulation. The modulated AM power output should be limited to 1300 watts peak with non-

symmetrical modulation that enhances the positive peaks.

UDIO

ISTORTION

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 "G

ROUNDING

" section on page 14 of this manual. More detailed suggestions on grounding

are available by requesting Ameritron's Tech Bulletin on RF Feedback.

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