[App_rpt-users] EMI/RFI issue

Benjamin L. Naber Benjamin at kb9lfz.com
Mon Jun 17 19:36:43 EDT 2013

I think I need to clarify.

the computher is a neoware CA-22 thin client. While it does have a power
supply module, it's cheaper to small the whole computer with a hammer
and buy a new one.

I have tested several different thin client machines with various OSs on
them, and all have the same issue.

I have a netbook that will accept 12Vdc into the power jack, and
connected that to a battery and radio, same RFI/EMI noise issue.

~Benjamin, KB9LFZ

On Sat, 2013-06-15 at 23:58 -0400, Benjamin L. Naber wrote:
> Greetings All,
> While thinking of a way I can turn my node into a portable allstar node,
> it has been discovered the computer I'm using, generates RFI/EMI over
> the DC power connection.
> The setup is as follows presently, which has zero *known* EMI/RFI
> issues. The radio is powered with an older linear 3A regulated power
> supply, which a parallel connection to a 12V 18Ah battery. All leads are
> kept short, under two feet. The radio is kept on 5W.
> The computer has a 12Vdc connection, and it's presently using an ac/dc
> SMPS, one that can be bought on eBay for about $10. 
> Both of these are plugged into the same outlet strip, and as stated,
> zero discovered EMI/RFI issues.
> The radio audio connections to the computer have the center conductors
> isolated with a 10nF cap. 
> Just as soon as I decide to power the computer from the battery, the
> radio has noise across every tunable frequency. Even if I disconnect the
> radio completely from the node, there is noise on the radio. From what
> is apparent to me, the noise is coming from the computers internal power
> supply section, riding the power wires back to the battery, and then to
> the radio.
> I see there are plenty of EMI/RFI filters I can purchase. However, I'd
> like to maintain the Amateur Radio Spirit of creation for this case, so
> I'd like some pointers on what I should test for, and construct some
> EMI/RFI filters.
> I have seen there are common mode and differential mode chokes filters,
> and some filters have both kinds of chokes. I'm not really sure the
> difference, besides the way the components are installed in the circuit.
> If you find it better to talk in person, contact me via allstar or look
> for my phone number on the internet.
> ~Benjamin, KB9LFZ
> Allstar node 28569
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