Limiting Electro-Magnetic Interference (Emi) - Samlexpower SEC-1235 Owner's Manual

SECTION 6
cela ne garantit pas qu'aucune interférence ne se produira dans une
installation particulière. Si cet équipement provoque des interférences
nuisibles à la réception radio ou télévision, ce qui peut être déterminé en
éteignant l'équipement, l'utilisateur est encouragé à essayer de corriger les
interférences en prenant une ou plusieurs des mesures recommandées dans
les paragraphes suivants.
6.2 UN-INTENTIONAL RF NOISE GENERATED BY SWITCHED MODE
POWER SUPPLIES (SMPS)
Switched Mode Power Supplies (SMPS) employ high frequency switching (30.5 KHz in
these units) and thus, are a source of radio interference, a recipient of radio interference
and a conduit of radio interference. (Older Linear Type, low frequency 50 / 60 Hz
transformer based power supplies do not employ high frequency switching voltages and
will be quieter as compared to SMPS).
The emission sources originate in the switching devices due to their fast switching
current transitions: harmonics of the switching frequency and broadband noise created
by under-damped oscillations in the switching circuit. The noise is both conducted and
radiated through the input power cord and the DC output wiring to the radio.
6.3 FILTRATION OF CONDUCTED NOISE
The conducted RF noise from this SMPS unit is limited to the maximum allowable levels by
internal filtration. The filtered RF noise currents (< few hundred micro Amps) are bypassed
to the chassis of the power supply. The chassis is, in turn, connected to the Earth Ground
pin of the AC input power cord (for Class 1 units). Thus, the filtered noise currents are
intentionally leaked to the Earth Ground. This is termed as the "Earth Leakage Current".
6.4 EXCESSIVE RF OUTPUT INTERFERENCE BY SMPS DUE TO
INCOMING RF INTERFERENCE WHEN POWERING RADIO TX / RX
SMPS 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. The receiver may "hear" the power supply. A slowly moving, slightly buzzing
carrier heard in the receiver may be caused by the antenna being too close. As with the
transmitter related noise pick up, a loose coaxial connector or a broken or a missing
ground may aggravate this problem. Normally, this noise will be below the background
| Limiting Electro-Magnetic
Interference (EMI)
SAMLEX AMERICA INC. | 15