[RFI] Alternative Power Source Questions

Jim Brown jim at audiosystemsgroup.com
Tue Feb 10 02:11:16 EST 2009

On Tue, 10 Feb 2009 01:43:30 -0500, Roger (K8RI) wrote:

>I believe the one problem discussed was from the inverter running with 
>solar panels wiping out the bands a city block away.

Yes, they can be very nasty noise sources. The fundamental problem is 
that the charging currents are pulse regulated, and the circuit 
designer has ignored fundamental design rules to prevent RFI. The 
problems include 1) fast rise times, so the current is rich in 
harmonics; 2) these currents flow around a loop area that is large, so 
the magnetic field produced by the current is quite strong; 3) the 
large current loop also results in strong antenna action for the higher 

These systems also use a system that pulses the battery to prevent long 
term degradation of the battery. I don't recall details, the the RFI 
implications are the same -- harmonics, large inductive loops, antenna 

Proper design would have the charging currents confined to twisted pair 
cable that follows the entire path from the regulator to the batteries, 
bypass capacitors across switching transistors to keep the higher 
frequency energy out of that path, and have the rise times slowed down 
to minimize the strength of higher order harmonics. 

Similar attention needs to be paid to the system that feeds power back 
onto the AC line, and a line filter should probably be used on that 


Jim Brown K9YC

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