http://elecraft.85.s1.nabble.com/250-Hz-and-400-Hz-Filter-Measurements-tp5300671p5303234.html
350 Hz, well aware of how close they are. I use the 350 setting for
difference between the two. Pulling in the roofing filter against a
Each to his own, just don't start a ban the 250 campaign. I know a
> Crew,
>
> I finally got around to dragging out my precision audio spectrum
> analzyer to check out the 250 Hz filters. I have two K3s, one
> with a single RX and one with two RS. I have 250 Hz and 400 Hz
> filters in all three RX.
>
> First, I tweaked the centering of each filter (that is, the
> offset), then I measured bandwidth at -6dB, -30dB, and -60dB with
> IF bandwidths of 1kHz and 250 Hz.
>
> Results: There was some variation from one filter to another, but
> trends are quite consistent. The only significant difference
> between the 250 and 400 Hz filters is at their -6dB points with a
> 1kHz IF, where the average bandwidths were 311 and 412 Hz
> respectively. This is essentially the bandwidth of the roofing
> filters themselves.
>
> Once you crank the IF down to 250Hz, there is no significant
> difference between the two filters. The average -6dB bandwidths
> were 193 and 200 Hz; at -30 dB, both filters averaged 300 Hz; at
> -60dB, they averaged 381 and 397 Hz respectively.
>
> There IS one repeatable difference between the 250Hz and 400Hz
> filters -- their insertion loss, which is 3dB. That is, the 250Hz
> filters have 3dB more insertion loss.
>
> After doing these measurements, I firmly agree with W4ZV, W0YK,
> and others, who have noted that there is no good reason for
> having both of these filters in a radio. Indeed, there is no good
> reason for the EXISTENCE of this particular 250 Hz filter,
> primarily because it is NOT a 250Hz filter by any reasonable
> measure.
>
> It is long past time for Inrad to lean on their filter supplier
> and get them to ship 250 Hz filters. Failing that, I want my
> money back for three filters. BTW -- all of these were purchased
> from Inrad, not Elecraft.
>
> 73, Jim Brown K9YC
>
>
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