[Elecraft] RFI, KUSB and MFJ-4225

[Ignacy]

The noise is never high, about 5 db over the morning noise. It occurs in
narrow spurs every approx 50 KHz. These move slightly as the output voltage
is adjusted.

It is possible that MFJ devices are refined over time. Mine is ca 1999.

Ignacy

On Wed, Oct 6, 2010 at 3:19 PM, Nick-WA5BDU [via Elecraft] <
ml-node+5608494-657492138-193087 at n2.nabble.com<ml-node%2B5608494-657492138-193087 at n2.nabble.com>
> wrote:

>   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
> >
> >
>
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