Continuous Carrier Modes - Acom 1500 Manual

amplifier at nominal power without changing drive at all. Use this approach to shorten the tuning
process duration.
c) Tuning Procedure.
While a continuous carrier (CW key down, RTTY or FM) signal at the desired frequency is still applied:
- Look at the upper scale (forward power); obtain maximum power using the upper (TUNE) knob;
- Look at the lower (Load Cap) scale and turn the lower (LOAD) knob in order to center the triangle
marker at the "!" mark.
- Release the PTT briefly in order to disable the attenuator, then repeat both steps at nominal power.
Always finish by peaking with the TUNE knob.
Appearance of an arrow on either left or right TRI scale edges means that the
LOAD knob position is far off. To correct this, turn the LOAD knob to the
prompted direction until the triangle marker appears inside the scale field.
Please note that the TRI mark will not appear until at least 5W drive is applied, and at least 20W
forward power is achieved.
If, for some reason, matching cannot be accomplished successfully, check the BAND switch position
and proper antenna selection. Then check the antenna VSWR at the same drive frequency.
d) Tuning hints.
While turning the knobs, note that both tunings would be virtually independent. This is a benefit of the
TRI. The plate-load resistance increases to the right and decreases to the left of the TRI center.
The scale center corresponds to the proper LOAD capacitor tuning, which presents an optimum load
resistance to the tube.
If you tune to the right, more gain will be obtained but less undistorted output power will be attainable.
You may prefer to use this tuning approach when your drive power is insufficient or when you need
less output but better efficiency, for instance at heavy duty modes (RTTY, SSTV etc.) where less heat
is wanted (not only in the amplifier but also in the transceiver).
Tuning to the left of the center would lead to the opposite: less gain and more power attainable. Of
course, this requires more drive power, more plate current, and more plate heat, which shortens the
tubes-expected life, as its cathode would be exhausted more quickly.
You might use the above off-center tuning hint also to compensate for mains voltage variations in
order to maintain tube efficiency: tune to the right when mains is higher, or tune to the left if it is lower
than the nominal voltage. Please see S.2-2 (Mains Voltage Selection) for more than 5% difference
from the nominal.

4-5. Continuous carrier modes

The maximum output power in continuous carrier modes such as RTTY etc. is 1200W. You may
exceed this limit up to about 1300W for short periods (one minute or less), while adjusting the drive
power for instance. Please have in mind, however, that the mean output power should not exceed
1200W for longer periods.
14
N O T E
Fig. 4-1. Using TRI tuning aid