[RFI] Astron fan circuit noise

dgsvetan at rockwellcollins.com dgsvetan at rockwellcollins.com
Fri Oct 15 10:01:07 EDT 2004


John,

I have had a SS-30M for over a year and have not experienced the problem on
80m, or any other HF or VHF/UHF band, to date.  Being an EMC engineer, I
could not resist opening up the unit after checking it out to see how
Astron got the switcher noise down, and the answer was obvious:  a lot of
ferrites and by-passing. You do not say if this problem just started or if
it has been there since Day 1.  Since my unit seems "clean" and the ARRL
lab tests on the SS-30 gave it a "clean" bill of EMI health, I suspect that
you have a problem in the fan driver circuitry.  Your description sounds
like a ramped PWM driver that is producing excessive spiking until it hits
full power output.  If this is a problem that developed only recently, the
extensive ferrites and by-passing are probably not designed to correct it.

If your power supply is still in warranty, I'd contact Astron.  If not, you
might want to consider replacing the fan.  If it is the brushless DC type
(which I think it is), the noise-making circuits are probably contained
within the fan itself.  Before going through that expense, though, you may
want to use a small "sniffer loop" connected to a receiver or spectrum
analyzer to isolate the noise source.  If you try that, be very careful, as
there is full line voltage and something around 300VDC on the primary side
of the circuits.  Don't try this if you are not familiar with switching
power supply topology or design.

Let us know what you find.

73, Dale
WA9ENA




                                                                                                                                       
                      "John Rader"                                                                                                     
                      <k5xtx at hotmail.co        To:       rfi at contesting.com                                                            
                      m>                       cc:                                                                                     
                      Sent by:                 Subject:  [RFI] Astron fan circuit noise                                                
                      rfi-bounces at conte                                                                                                
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My Astron SS-30M makes noise on 80m each time the fan starts. The noise
starts out low in pitch and increases for about 10 seconds then stops. The
fan continues to run for about 30 more seconds. It is not related to fan
speed or duration, only starting.

Any Ideas on how to eliminate this noise?
John K5XTX

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