[Orion] Roofing filter selection - Eh?

[Bill Tippett]

Hi Dan,

         Let me take your questions in reverse order.
Stay with me because you will like the final answer.

 >Can someone explain to me why I need to set the BW to 1990 hz to get the
2400 hz roofing filter, instead of 2390 hz?  Or, to put it more precisely
since I know this is operating as designed, "why was the radio designed this
way?"

         Ten-Tec apparently uses an algorithm which selects
roofing filter bandwidth in Auto when DSP is set to ~75-80%
of nominal.  Hence the 2400 switch point is at DSP ~2000 Hz.
The logic of this was apparently to ensure that DSP operates
in the flat gain area of the roofing filter and to avoid Group
Delay effects that can occur near the edges.

 >I was reading through the new manual tonight in preparation for the Sprint,
and I was shocked - yes, I think shocked is the right word - to read that
the AUTO roofing filter selection chooses the 2.4 khz roofing filter when
the BW setting is less than 2.0 khz.  I had naively assumed for the last 15
months that I got the 2.4 khz filter when I set the BW to less than 2400 hz
- say 2390 hz for example.  I now know that that isn't true, but I don't
understand why.

         The simple solution is to use Filter>Menu to lock your desired filter
in place.  Using Auto is especially bad if you have an 1800 Hz filter since
it is not switched in until 1400 Hz...far too low for SSB intelligibility.

         The good news is that the Filter>Auto switch points are being looked
at for modification in the next firmware revision.  I'm not exactly sure
what the final release will do but I'm fairly certain the SSB filter issue
you described will be fixed.

                                                 73,  Bill  W4ZV