[Elecraft] RFI, KUSB and MFJ-4225

[Nick-WA5BDU]

  I was surprised to hear of the MFJ-4225 generating noise on 160, since 
I use a MFJ-4225MV and work 160 a fair amount, yet hadn't noticed any 
noise.  OTOH, I could I tell if I'm hearing P/S generated noise as 
opposed to "other" 160 meter band noise?

I dug out my homebrew linear supply and decided to use the AFV reading 
on the K3 for comparisons.  With AGC off, antenna connected, K3 tuned to 
an empty spot on the band with no signals present (daytime).  The 
readings jump around a fair amount with random bursts of noise and 
possibly QRN crashes, so I jotted down ten or so over a ten second 
period, first with the MFJ powering the K3, then with the linear P/S, 
and then back to the MFJ to close the loop.  I know this isn't highly 
rigorous, but it should tell me something.

The average readings were MFJ, 146; linear, 168; MFJ, 141.  I don't 
think the differences are significant, that is, I don't think the linear 
power supply is noisy.  So I'd say there's no significant difference.  I 
turned on the MFJ while listening with the K3 powered from the linear 
P/S and didn't hear any noise increase.  The MFJ had long leads 
attached, going to my IC-706, but not loaded.

Looking at the QST product review (January, 2000), they found that the 
MFJ-4225 was very quiet with some increase in noise between 7.5 and 10 MHz.

Maybe there's something wrong with your specific power supply.  I guess 
it's also possible that a change in manufacturing techniques or design 
has caused the MFJ-4225 to degrade.

73-

Nick, WA5BDU



On 10/5/2010 7:38 PM, Ignacy wrote:
>
> MFJ-4225 generates a 10db noise on 160m. Can a simple filter cure the
> problem or is it better to get a linear PS?
>
> Ignacy, NO9E
>
>