[Elecraft] 250 Hz and 400 Hz Filter Measurements

[Joe Subich, W4TV]

Jim,

 > There's something different about the K3 Sub-RX, and the Roofing
 > filters seem to fall apart below about -25dB. Makes a guy wonder
 > what's going on!

I would bet the subreceiver has excess gain in the IF and you're
seeing amplified IF noise (particularly since the bandwidth is
about 1 KHz).  I don't see any way for the K3 Utility to calibrate
main/receiver gain separately (Dick?) but I'd suggest checking the
gain calibration of the subreceiver or measuring all of the filters
only in the main receiver.

73,

    ... Joe, W4TV

On 7/16/2010 3:28 PM, Jim Brown wrote:
> On Fri, 16 Jul 2010 14:38:24 -0400, Guy Olinger K2AV wrote:
>
>> Each to his own, just don't start a ban the 250 campaign.
>
> Both you and Ed raise good points. No intent there -- I agree that
> the so-called 250 Hz filter is slightly more useful than the 400
> Hz. My real objective is to get Inrad to clean up their act!  BUT
> -- take a look at the data in this link. Lots of food for thought.
> There's something different about the K3 Sub-RX, and the Roofing
> filters seem to fall apart below about -25dB. Makes a guy wonder
> what's going on!
>
> http://audiosystemsgroup.com/K3FilterStudy-250HzRoof.pdf
>
> 73, Jim K9YC
>