Limiting Electromagnetic Interference - Samlexpower SEC-1212 Installation & Operating Manual

LIMITING ELECTROMAGNETIC INTERFERENCE (EMI)
This equipment has been tested and found to comply with the
limits for a class B digital device, pursuant to Part 15(B) of the FCC Rules.
These limits are designed to provide reasonable protection against a
harmful interference in a residential installation. This equipment generates,
uses and can radiate radio frequency energy and, if not installed and used
in accordance with the instructions, may cause harmful interference to
radio communications. However, this does not guarantee that interference
will not occur in a particular installation. If this equipment does cause
harmful interference to radio or television reception, which can be deter-
mined by turning the equipment off and on, the user is encouraged to try to
correct the interference by one or more of the following measures:
•
Reorient or relocate the receiving antenna.
•
Increase the separation between the equipment and receiver.
•
Connect the equipment into an outlet on a circuit different from that to
which the receiver is connected.
•
Consult the dealer or an experienced radio / TV technician for help.
7.
SWITCHING POWER SUPPLIES AND RF NOISE
1. Switched mode power supplies ( SMPS ) employ high frequency
switching and thus, are a source of radio interference, a recipient of radio
interference and a conduit of radio interference. ( Older linear type trans-
former based power supplies do not employ high frequency switching
voltages and will be quieter as compared to switching type of supplies ).
2. The primary emission sources originate in the switching devices due
to their fast switching current transitions: harmonics of the switching fre-
quency and broadband noise created by under-damped oscillations in the
switching circuit. The secondary source is from the bridge rectifier, both
rectifier noise and diode recovery. The AC input rectifier / capacitor in the front
end of the switching power supplies ( excepting those with power factor
correction ) are notorious for generating power supply harmonics due to the
non linear input current waveform. The noise is both conducted and radiated
through the input power cord and the DC output wiring to the radio.
3. Switching power supplies are also recipients of radio interference.
The normal operation of the power supply can be disturbed due to RF noise
getting coupled into the power supply. Thus, the power supply may generate
excessive RF noise and lose output voltage regulation due to excessive
transmitter energy being coupled through the AC / DC lines to the power
supply's regulator feedback path. This may be due to antenna being too
close or due to the antenna or feed system not radiating properly. First
check the antenna system SWR. Then, if necessary, relocate either the
antenna or the power supply farther apart.
8.