N5OP:
>I never knew this. My 566 is decked out with all the filters, but I
did not know that the 566 dispensed with the extra IF amplifier stage
for the 500 and 250 Hz filters. This is good to know, but how is the
extra insertion loss dealt with?
Kim nobody answered your question so I'll try. The
566 uses 4-pole filters which have lower insertion loss
than the 6-pole 250 Hz #219 or the 8-pole 500 Hz #217. Thus
the extra amplification stage was unnecessary (just like the
4-pole 600 Hz Inrad #762 for the 565 which uses one stage only
for the 1000 Hz and above filter slots).
Regarding the #219's IMD performance, I'm not aware that
anyone ever measured it in an Orion 565. There might be
several reasons it works better than the #217:
1. It's a better match to the gain of the second amplifier
(one fixed 12 dB gain amp for both the #217 and #219, which
was apparently too much for the #217 filter).
2. It's bandwidth is half that of the #217 so its IMD
performance should be better, all other things being equal.
3. It's 6-pole instead of 8-pole. IMD is black magic and
there can be significant differences between filter types.
73, Bill W4ZV
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