[Elecraft] 500Hz 5-pole vs Inrad 500Hz 8-pole?

[Joe Subich, W4TV]

 > Is either one/both wide enough for 500Hz Olivia modes?

I would question using either 500 Hz option for Olivia since the
group delay will be significant in the shoulder areas and that
can impact the "outer" tones considerably.

 > Any thoughts on the merits of one vs the other?

My Elecraft 500 Hz, 5-pole filters averaged 480 Hz at the -6dB
points while the INRAD filters tend to be about 10% (or more)
wider than nominal, particularly as the nominal bandwidth
decreases.  On the other hand, the skirts are much sharper (better
shape factor) with the 8 pole filters.

 > does the 8-pole Inrad filter not need to be matched?

There is no "matching" for the INRAD filters but their center
frequencies are not well controlled.  In a recent sample of
four 400Hz INRAD filters, I measured offsets at -15 Hz, +24 Hz,
+45 Hz and + 55 Hz.  The total difference of 60 Hz in 430 Hz
(average) measured bandwidth is a bit concerning.  I ended up
with the -15 Hz/+24 Hz pair in one rig (no offset) and the
+45 Hz/+55 Hz pair in the other rig with a slight offset to
center the pair.

73,

    ... Joe, W4TV


On 1/25/2011 9:27 AM, Ross Primrose wrote:
> Any thoughts on the merits of one vs the other? The 5-pole filter is
> cheaper, but they need to me matched for diversity receive, does the
> 8-pole Inrad filter not need to be matched? Is either one/both wide
> enough for 500Hz Olivia modes?
>
> Thanks...
>
> 73, Ross N4RP
>