Acom 700S User Manual page 26

Place as far away as possible (also by height) the radiating elements of antennas from the
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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
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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);
Improve the RF grounding system: use the shortest and widest possible metal strips for the
•
connections to ground and between the different gear in the shack; connect one or more
counterpoises (sized for the problematic band) to the feeder shield at the point, where it
enters the building, and the same point - with the possibly shortest and widest connections -
to the grounding system: this is a very efficient measure, in particular if the shack is located
on a high floor above ground;
To reduce the RF impedance of the grounding connections sheet metal stripes instead of
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flexible braids are preferred;
Thread ferrite beads or snap-in ferrites with medium permeability (800-4000) over the power
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cord, the feeder and the signal cables leading to the affected devices (TV etc); besides the
size, consider the frequency range in which the offered ferrites are effective - normally they
are optimized for suppression of interferences on HF (with larger permeability), with medium
permeability for HF-VHF or with low permeability - only the VHF range. The latter are
ineffective for HF;
Whenever possible use shielded cables and ground their shields at both ends;
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The addition of even quite simple low pass L/C or R/C filters directly to the disturbed inputs
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or outputs of the devices is very effective, provided it is practically applicable.
Last but not least, bear in mind that the benefit of the above measures is two-fold.
Firstly - they reduce the interferences from your transmissions to the ambient environment and secondly -
they reduce the background noise floor for your reception.
Practically, with no great efforts, implementing the above measures, you can reduce the receive
background noise floor with one or more S-units across the different bands. This will allow you not to miss
weaker stations, which will hear you because of your increased transmission power.
And third, but very important: the EMI environment at your station will become safer for you and those
close to you.
Page 26 of 52 | S e c t i o n FIRST POWER-ON, CONTROL SYSTEM, AND INITIAL CHECK
User's Manual | ACOM 700S | 1.8-54 MHz Linear Amplifier
May 2021