[RFI] RF Limited DF4000 Low Pass Filter

[W0UN--John Brosnahan]

At 08:27 AM 1/4/2003 -0700, Richard Zalewski wrote:


>Anyone have any experience with this filter?  I heard it was marketed by RF
>parts at one time but an internet search finds nothing on this filter.
>
>Dick W7ZR

I have a couple of the larger ones--don't recall if they are the 7000 or
the 10,000.  Unfortunately they are in Colorado and I am in Texas
now--so I can't be sure.  (Pretty sure they are the 7000)

I put them on my network analyzer (HP-4195) and looked at them
very closely.  Very good roll-off above 30 MHz--but there were a
few minor ripples in the 100-500 MHz range, due to minor spurious
resonances.  But these resonances were still more than 40 dB down
and very narrow.

I certainly feel the bigger ones I have are good filters--although they
did have a minor SWR ripple on 40M--about 1.3-1 when on the
dummy load.  They appeared to be well made with heavy duty
coils and in my units the caps were fabricated from Teflon sheet.

ONLY disappointed was the 40M SWR issue--but I figured that
I would look at them at some point and see if I can tweak them a
bit to reduce that to something closer to 1.1-1.

John   W0UN