Topband: FT-2000 for serious TB DXing?
kolson at rcn.com
Fri Jun 1 11:24:08 EDT 2007
> Indeed ! In fact, compare these FT-2000 numbers with the QST review of
> FT-1000MP + Inrad roofing filter in February 2005 QST. The FT-2000, with
> built-in Yaesu roofing filters, has worse 2 kHz IMD numbers than an
> without any roofing filters whatsoever ! How could they have screwed up
> FT-2000 design so badly ?
> Steve, N2IC
Well, let's look at the numbers:
FT-1000 MP FT-2000
20Kc 94 db 100 db
5 Kc 76 db 86 db
2 Kc 69 db 63 db
Unfortunately, no IP3 was given for the FT-1000, so we can't look at that.
As you can see, the 1000 is 6 db better than this sample of the FT-2000 at 2
kc, but the FT-2000 is better at the other spacings, 10 db better at 5 kc!
So which one is better depends on where your unwanted signal is. At these
short spacings what is being measured is largely the efficacy (and accuracy)
of the roofing filter.
I am not sure how the consistancy in terms of bandwidth and accuracy in
center frequency these filters turns out to be, but it should be pointed out
that the bandwidth/center frequency percentage is very small! In the INRAD
review, the reviewer states that the INRAD filter started to improve the IMD
for "signals farther apart than a 1 Kc spacing". Considering that this
roofing filter is supposed to be 4 kc wide, this smells funny. It should
only START to improve at 2kc (half the bandwidth of the roofing filter) if
the center frequency is correct relative to the later CW filter and the
filter truly is 4 kc wide. Of course, if the center frequency of the filter
is off, the skirts of the roofing filter would kick in sooner. On one side
of the carrier frequency! On the other, it would be worse. Conjecture to be
sure, but curious. Maybe what we need is a IF shift control for the roofing
filter relative to the next CW filter so that we can "shade" the skirt of
the roofing filter on the right side of the CW filter!
What comes out of this is that the Ft-2000 is probably designed well, but
that the roofing filter may leave something to be desired. CQ INRAD...
Regards, Kevin K3OX
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