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Switching power supply for ATLAS-210

The idea is to use  a PC power supply to feed the ATLAS-210 .A typical PC power supply provides at least four DC voltage (+5 , +12 , -5 , -12 ) .ATLAS 210 is only asking for 13.8 volts with up to 16 amp (peak value) . Several descriptions appeared in various magazine like ELEKTOR (6/2003 issue)   and MEGAHERTZ MAGAZINE (march 2005 issue) .We prefered to follow the indications given  by F1LVT in the latter magazine (please refer to march 2005 issue page 24 to 29 , to get the magazine chick here  MHZ MAGAZINE ). Nowadays it is still very easy to get surplus PC power supply for almost nothing  as an old PC is a waste that is even costly  to get rid of . The first thing is to select a power supply giving a low level of HF signal in the 3.5 mhz band and rated  at least at 200 watt minimum .

You cut all wires coming out of the supply keeping only the various 12 volts wires which are soldered together and also 1 wire giving 5 volts  . In order to boost the ouput voltage from 12 volt to 13.8 volt locate the Pulse Width Modulator which drives the switching  transistors .It is the brain of the supply !  Generally  it is a small digital circuit  (reference TL 494 or something  else ending with 494   having 16 pins ) .To increase the output voltage  you only have to put a resistor between pin 1 and 7  .The value has to be adjusted in order to get the 13.8 volts at the output .(the value is between 10 and 20 Kohms ) .It should be noted  that for some power supply ,to have  a good regulation of the output , it is necesary to load the 5 volt circuit  with a resistor in order to have some current anywhere between 0.5 and 1 amp . To get a reading of  the output voltage with a good sensivity it is a good practice to measure it with a meter in serie with a zener diode of 10  or 12 volts and a resistor so to have a scale starting at 10 or 12 volt and ending at 15 volts .It is also a good idea to put an AMP meter (0 to 20 amp on the ouput  .You put everything in a box .You are all set !

Get full diagramm of standard switching power supply

Four power supply where done according to this design  and they operate without any problem on 2 ATLAS-210 and two  VHF / UHF transceivers .No problems of QRN or QRM due to the power supply  on any band even on 3.5 mhz  .Keep on going .

On some recovered power supply you can be bothered by some small birdies , which are harmonics of the frequency used by the power supply .This can be observed mainly on the low bands (3.5 mhz) .Generally on that band the noise signal is quite high  and this is not a problem .However if it is not the case  and if the signal of your fellow contact is not very strong  and if  his signal is right on the harmonic  this can be annoying .That is why  it is a good idea to put  a QRN SHIFTER  .THis is a  quite simple add on .It consists of a simple resistor which is put in parallel of the existng resistor R16 (see the following diagram) .THis resistor in conjunction with C11 capacitor defines the working frequency of  the power supply .If you add through a switch a resistor in the 47 k range you will be able to shift the frequency to clear the frequency that you are listening either on 3.5 or 7 mhz band .

Detailed view of the regulator circuit of a typical switching power supply

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