----- Original Message -----
From: "John Rippey" <w3uls@3n.net>
> Finally, with the new roofing filters forthcoming from INRAD, a bunch of
> older radios soon are going to have sterling dynamic range capabilities,
> and you won't have to jump through hoops like the mods required on the
> TS-870, or shell out big bucks.
snip
> I wonder if George's new filters will have the effect of discouraging
> introduction of new ham rigs since the older ones are being given such
> powerful new legs?
snip
This will be an interesting one when the full story is told. Certainly so
far as the FT1kMP is concerned. The roofing filter from Inrad has a 4 kHz
b/w which makes quite a good choice for SSB but is a lot of b/w for CW.
Interestingly, the filter requires some additional amplification to get over
its insertion loss and I understand that Inrad have opted to include enough
amplification to get over that loss and add a little bit more. What price
that extra amplification?
Figures published by Rob Sherwood
http://www.sherweng.com/Dayton_2004/Dynamic_Range_Data.pdf
show the following dynamic range numbers at 2 kHz:-
TT-Orion 1 kHz roofing 92db
FT1k MkV 70db
FT1k 69db
FT1kMkV Field 60db
Sherwood also states that an additional 6-7db improvement in IMD at 2 kHz is
obtained with the Inrad 762 filter. This puts Orions range at 2 kHz up to
98db or better. That's a full 28db better than the FT1k MkV and 38db better
than the Field.
That's a big gap and one that can only widen when the roofing filter mod is
added. The question is by how much? As a CW man, I wonder whether the
benefit in improved IMD at 5 kHz will outweigh the deterioration in IMD at 2
kHz. I have an MP but for now my roofing filter dollars will stay in my
pocket. Time will tell.
Bob, 5B4AGN
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