User's Manual | ACOM 500S | 160-4
m Linear Power Amplifier
March 2023
S e c t i o n FIRST POWER-ON, CONTROL SYSTEM, AND INITIAL CHECK | Page 33 of 66
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In case you use asymmetric antennas (GP and similar) install as many radials as practical (use
a well-developed counterpoise system);
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Add current chokes on the coaxial feeders;
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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);
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If the use of asymmetrical directly fed "wire" antennas is inevitable, use mainly half wave or
half wave multiple lengths - 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 odd 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);
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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;
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To reduce the RF impedance of the grounding connections sheet metal stripes instead of
flexible braids are to be preferred;
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Thread ferrite beads or snap-in ferrites with medium permeability (800-4000) over the power
cord, the coaxial 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;
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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 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.
