Acom 700S, Operating Manual, Page: 16 / 30

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Upon reaching 700W forward power check the following parameters (continuous carrier operation):
- the reflected power must not exceed ~78W (for SWR 2:1) or better still to be below 28W (for
SWR 1.5:1);
- PA DC CURRENT must be between 23 and 30A; it is normal that the current varies within these
limits when changing operating frequency and antenna impedance;
- PA DC VOLTAGE must be within 42 – 44V;
- the transceiver’s SWR reading must be below 1.2:1.
Enter the MEASURE menu and check:
- the drive power from the transceiver must be between 15W and 40W;
- PA BIAS, which must be between 2.4 and 2.8V;
- PA TEMPERATURE, which must be between the ambient and 95ºC (203ºF), depending on the
power level and the duration of transmission.
f) Elimination of electromagnetic compatibility (EMC) problems.
If you use an amplifier for the first time in your shack, you may need to make some improvements in the
setup. It is possible you might experience tingling from metallic objects due to the stronger radiated RF
field. It could affect the operation of your station or systems outside, if they are too sensitive – typical
examples are the microphone, CW keyer, computer keyboard / mouse, as well as TV receivers, Hi-Fi,
intercom or telephone setups and others.
For instance, induction of RF currents into the microphone, CW keyer or computer keyboard, may lead
to distortion in the peaks or self-oscillation in SSB mode, “sticking” or breaking off the dots or dashes
from a Morse keyer, or garbling computer screen images. For the elimination of such problems we
recommend that you take the following general measures:
- minimize the radiation from the feed lines by reducing the common mode currents in them,
improve the balance of antennas and feedlines;
- in case you use asymmetric antennas (GP and similar) install as many radials as practical (use
a well-developed counterpoise system);
- add current chokes on the coaxial feeders;
- place as far away as possible (also by height) the radiating elements of antennas from the
premises, where the affected devices are located; in this sense, asymmetrical antennas without
a separate feeder (Long Wire, Windom, and similar) may cause more interference because their
radiating element begins immediately from the shack (part of it is the feeder itself);
- if the use of asymmetrical directly fed “wire” antennas is inevitable, use mainly half wave or half
wave multiple – they have a high input impedance, operate respectively with a small current
in the feed point, and in the grounding of the shack; thus you can reduce the strength of the
disturbing RF fields more than 10 times (at the same radiated power) compared to the case
with quarter-wave and multiple to quarter-wave antennas of this class – you should avoid them
because they have a low input impedance and operate with a large RF current in the grounding
system and in the power supply network respectively, i.e. they create stronger disturbances
(RFI);