The problem with the 500 and 250 Hz filters is the design of the filter
board itself. Let me try to explain.
The filter board is designed for one bank of five filters and one bank of
two filters. When either the 250 or 500 Hz filters are selected, being in
the secondary bank if I can call it that, the 20 kHz filter is switched in
ahead of either. Since both the first filter bank and the second filter
bank have filter loss amplifiers ahead of the filters, that puts two filter
amplifiers in the filter train when either 250 or 500 Hz filters are
selected.
There is some talk of switching in the 2.4 kHz filter ahead of the 250 and
500 Hz. This would be in lieu of the 20 kHz filter that is currently
switched. This mod would provide a bit more capability to reject close in
interference by the two narrow filters but is not a final answer.
The fix for this is twofold. One, a redesign of the filter board so that it
incorporates one bank of seven filters is required. This would allow TenTec
to have one amplifier to overcome each filter's loss. The other cure which
should be incorporated at the same time would be to design filters
especially for the Orion instead of using Omni 6 filters which was expedient
for TenTec in the first place and an economic decision.