[TenTec] Redesigning the filter section of the Orion IF

[Bill Tippett <btippett@alum.mit.edu>]

W9OY wrote:
>Given the results of the INRAD 600hz filter replacing
the 1khz filter in the Orion, has anyone looked at
modifying the IF board to include all filter position
in parallel?

>From looking at the schematic, it looks to me you
could cut a couple of traces, re-route the signal and
add a nand gate and a couple of steering diodes to
have all the roofing filters positions available ahead
of the offending amplifier.  You would need the custom
filters, but given the apparent ease of modification
and ready reversibility, it looks like this could be
done fairly easily.  I haven't measured anything yet,
just brainstorming.  Has anyone considered this?

        Orion's firmware assumes the 500 and 250 filtersare at 9.000750 
instead of 9.001500 which all the
other filters use.  Therefore you cannot use the
Inrad #352 in the current 500 position.  Likewise
you cannot put the Ten-Tec 217 or 219 into the
1000 position.  Doing either of these would result
in misalignment of IF offsets, etc.  To do what you
describe would require two new filters...a 4-pole
500 and 250 Hz, at a center frequency of 9.000750
and with low insertion loss.

        A 4-pole 250 Hz filter does not presently exist.
To avoid the second stage of amplification, insertion
loss should probably be no more than 4 dB as is the
case for the Inrad #352.  It would be interesting
to see what a 4-pole 250 Hz would look like for
insertion loss and shape factor but I am not aware
of any currently available.

        Just as an update for all, Inrad is no longer
offering the #352 as a kit but will be offering the
same filter as #762 in a completely assembled unit.

        Until Ten-Tec may change the layout or firmware
(both are required), the #352/762 is a very clean
solution.  I put mine into the 1000 position and
moved my 1000 to the 1800 position.  I store my 1800
in the 500 position which I have disabled and can
quickly swap it into the 1800 position for my once
annual SSB contest (CQ WW).  Auto-Filter works fine
in CW with the 1000 switching in at DSP = 1400 Hz and
the 600 switching in at DSP = 750 Hz.  You cannot really
use the 1800 with Auto-Filter anyway since it does not
switch until DSP = 1400 which is far too low for SSB.

                                        73,  Bill  W4ZV

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