Samlexpower SEC-1223, Owner'S Manual

16  |  SAMLEX AMERICA INC.    

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 
or “band” noise. Increase the separation between the power supply and the receiving 
antenna. Use an outdoor antenna. This will reduce the amount of signal picked up from 
the power supply and also increase the amount of the desired signal.

6.5  ADDITIONAL GUIDELINES FOR REDUCING RF NOISE

•  Use additional appropriate AC Radio Frequency Interference (RFI) Power Line Filter 

rated for minimum 10A immediately before the AC input of the power supply. 
Filtered, Ferrite Coated Cord Set is another choice. These cord sets, with integral 
line interference filters, reduce Common and Differential Mode Interferences 
over a wide frequency range. Because they are shielded, they are also effective 
against radiated interferences. In addition to the built-in filter networks, the 
cable conductors are coated with an RF absorbing ferrite compound. This provides 
additional attenuation at high frequencies that is lacking in most regular LC filters. 
The RF absorption of the ferrite-coated cable avoids resonances at high frequencies, 
reducing the conducted and radiated RF noises even further.

•  Use additional appropriate DC radio frequency interference (RFI) power line filter 

rated for minimum 30 A immediately after the DC output of the power supply. 

•  Twist the Positive and Negative wires from the output of the power supply to the radio.

SECTION 6  

|   Limiting Electro-Magnetic 

Interference (EMI)