Topband: 160m noise

[Michael Tope]

----- Original Message -----
From: "Jeff Maass" <jmaass at columbus.rr.com>

> Did you wrap coax, audio cable, or something else
> for your test?

For convenience, Jeff, I just used a piece of stranded
insulated wire (I think it was #16). The impedance you
get a low frequencies should be the same regardless
of the wire size (within reason). At higher frequencies
(above ~10 MHz) where the distributed C comes into
play, it will make a difference, however (a fat wire like
a coax shield will probably have much more distributed
C than a thin wire).

> Running an unpracticed eye across the data sheets
> for the two materials, it looks like #78 material
> has a somewhat better mu-s data curve for 160,
> although the two materials look pretty close in
> most areas. The Resistivity of the #78 material
> is twice that of #77.
>
>
http://www.elnamagnetics.com/library/catalogs/fairrite/14th_rev2/77_Material
.pdf
>
http://www.elnamagnetics.com/library/catalogs/fairrite/14th_rev2/78_Material
.pdf
>
> This would be more significant if one could actually
> find a place to *buy* toroids of #78 material, which
> doesn't seem possible at present. Perhaps #78 is too
> new to have made it into distributors' stock yet?

Yes, I agree, Jeff, it looks like type 78 would be somewhat
better for 160. I've never tried to source it, however, so I
don't know anything about availability.

You might also look at the new Fair-Rite Products 31
material. It looks like they have tried to fix the resonance
problem that Tom W8JI mentioned. From the Fair-Rite
catalog:

"A new MnZn ferrite designed specifically for EMI suppression
applications from as low as 1 MHz up to 500 MHz. This material
does not have the dimensional resonance limitations associated
with conventional MnZn ferrite materials"

The mu-i is not as high as 77/78, but it maintains a high
mu-s" (term responsible for resistive component of complex
impedance) to a much higher frequency. This would probably
be a good choice if your looking for good suppression over
the whole HF and lower VHF bands (as opposed to just 160
meters).

73 de Mike, W4EF.................................