[App_rpt-users] EMI/RFI issue

Benjamin L. Naber Benjamin at kb9lfz.com
Sat Jun 15 23:58:39 EDT 2013

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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