Re: CW narrow filter


Michael Kopec
 

Hello Rich VE3KI.  To get the filter specs now, according to elecraft webmaster, you must email tech support and they will send them to u de Mike K8NS

On Monday, November 26, 2018, 5:54:46 PM EST, ve3ki <ve3iay@...> wrote:


Thank you, Joe. I wanted to be able to point to the Elecraft plots, but I was unsuccessful when trying to find them on the new web site - thanks for the link.

73,
Rich VE3KI


On Mon, Nov 26, 2018 at 02:49 PM, Joe Subich, W4TV wrote:
If you find you really need one, I'd suggest the 200 Hz filter,
because the 250 Hz filter is actually not all that much narrower
than the 400 Hz filter (333 Hz vs. 464 Hz at -6 dB, according to
> <http://audiosystemsgroup.com/K3FilterStudy-250HzRoof.pdf>).


I would choose to believe the measurements made by Elecraft at:
<https://elecraft.com/pages/k3s-8-215-mhz-first-if-crystal-filter-response-curves>


The Elecraft curves show the -6 dB response points at roughly 480 Hz
for the "400 Hz" filter (KFL3C-400) and 370 Hz for the "250 Hz" filter
(KFL3A-250) both of which are actually made for/imported by INRAD.

The Elecraft application note also includes a comparison of the
KLF3A-250 vs. KFL3C-200 which shows the 200 Hz filter is tighter
than the 250 Hz filter to at least -50 dB (where the bandwidth
of both is approximately 700 Hz).

73,

... Joe, W4TV


On 2018-11-26 11:53 AM, ve3ki wrote:
To start with, try just using the Width and Shift controls. You can narrow the DSP bandpass down to 50 Hz, independently of what roofing filters you may or may not have installed. See <http://www.nccc.cc/archived_meetings/pdf/K3%20Filters,%20Jan%202009.pdf>.

If you find that strong signals inside the 400 Hz filter bandpass but outside the narrower DSP bandpass are often causing AGC pumping or IMD problems that you can't eliminate with the Shift, Width and AGC controls, a narrower roofing filter might help. If you find you really need one, I'd suggest the 200 Hz filter, because the 250 Hz filter is actually not all that much narrower than the 400 Hz filter (333 Hz vs. 464 Hz at -6 dB, according to <http://audiosystemsgroup.com/K3FilterStudy-250HzRoof.pdf>). I believe that a lot of the difference seen by users who have both is primarily due to the narrower DSP width setting.

73,
Rich VE3KI

On Mon, Nov 26, 2018 at 10:46 AM, john ni0k wrote:


Operating the CW WW CQ contest makes me wish for something narrower than
the 400 Hz filter in my rig currently. I know Elecraft has a 200 Hz
filter but is there something else that people are using?

73,
-John NI0K

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