6
AMERITRON
116 Willow Road
Starkville, MS 39759
Tel: (662) 323-8211
Fax: (662) 323-6551
AMPLIFIER CIRCUITRY
Wattmeter Circuits
The BIAS/WM/ALC board contains the peak power detector circuits. The rear panel
directional coupler connects to IC101D/C. IC101D/C drives Q101/102 to charge
C103/106 to the peak voltage from the directional coupler. C103/106 is lightly loaded by
IC101A/B and R103/107. This allows enough "hang" time for the meter to accurately
indicate peak power levels.
Accurate forward peak power reading are obtained under mismatched load conditions
when the reflected power is deducted from the forward power readings.
The average and peak envelope power values are EQUAL on CW, FSK and FM (modes
that do not have amplitude changes in the carrier). The average power level of voice or
other complex waveform signals has NO SET RATIO of peak to average power.
ALC (Automatic Level Control)
The ALC circuit functions by using a comparator (IC103A) to reduce the exciter drive
power if the output power of the ALS-600 exceeds a preset value. The ALC circuit also
reduces the drive power if the SWR increases while operating with the ALC controlling
the amplifier output power level. The ALS-600 ALC output should be connected to the
proper exciter external ALC connection point with a shielded audio type cable. Consult
the exciter manual for the proper exciter connection details.
Operation at high audio gain levels on SSB with ALC has the same effect as an RF
speech compressor. RF compression increases SSB "talk power". Background noise
pickup also increases when the exciter gain is operated at high levels to increase
compression. Audio distortion does not normally occur with this type of speech
processing if the ALC circuit in the exciter is properly designed.
Do not attempt to limit the CW power more than a few percent solely with the amplifier
ALC circuit. Using the amplifier ALC to reduce CW power levels may result in pumping
of the output power during dots and dashes. The "ALC SET" control will be correctly
adjusted when the "ALC" LED gives a small flash while transmitting on CW. This can
be accomplished by adjusting the "ALC SET" control on the front panel so that the
"ALC" LED just barely lights when the desired power level (below 400 watts) is reached
with a steady carrier.
