[Elecraft] Hearing the effect of narrower roofing filter

[alsopb]

Guy,

Wouldn't a deep, tunable narrow notch filter also be a solution.  
The present notch filter is as wide as a barn door and useless for CW.  
I'm not a DSP programmer, but wonder how hard it could be to implement one.

After there is a narrow "notch" in the present RTTY dual passband filter.
If one can do a double hump filter with notch in the middle, why not just a
narrow notch filter?

73 de Brian/K3KO  




Dick Dievendorff wrote:
> 
>     ..... Maybe
> I should have ordered the 200 Hz 5-pole instead, but I got it into my head
> that maybe the 8-pole filters were "better" in some way.  I didn't repeat
> this mistake when I ordered filters for the subreceiver.
> 
> Dick, K6KR
> 
> I know I will incur some religious wrath from some.... however here is the
> OTHER side of that argument.  It's not that I am denying the issues that
> are raised to question getting the two 8 pole CW filters (400 and 300 in
> actuality).
> 
> I am solving a SINGLE happenstance which occurs over, over, over and over
> again in contests, so much so that until the K3 it was in my mind the
> LIMITING issue in improving 40m CW DX scores. 
> 
> I am at a contest station in eastern NC just off Pamlico Sound. On 40m to
> Europe we are using a 5 element wire quad suspended across a 220 foot
> NE/SW catenary between two towers. 
> 
> Broadcast signals above 7.1 routinely peg meters and light all the lights. 
> So do some US stations in the NE, and so do some number of VERY LOUD
> European stations (VLS).  WHAT they are doing to be so loud is not part of
> my exposition. They just are very loud.
> 
> At some point in the contest, one has worked all the VLS, loud, medium and
> well-antenna'd QRP signals. What remains is a bewildering and seemingly
> bottomless pool of stations that can hear us (QRO on 5 elements) and are
> trying to work us on antennas with the gain of a basement floor joist wet
> noodle antenna. There are hundreds and hundreds of these. We have some
> number of recordings made in Europe of these, and they are quite weak over
> there. 
> 
> It is guaranteed, only a matter of time, and sometimes immediate, that a
> VLS will settle in the next slot above or below. They may be as close as
> 350 Hz. The problem now is working the QRP wet noodle station who is into
> the noise without hardware AGC pumping or other effects from a VLS INSIDE
> the roofing filter that was set to hear stations who will call sometimes
> +/- 200-250 Hz.  
> 
> I need the roofing filter is to get down 30 db as quickly as possible,
> without giving up too much of the +/- 250 Hz. The 400 Hz is a good width
> even for VLS +/- 500 Hz.  If a VLS squeezes me on one side, I only want to
> give up +/- real estate in the roofing filter on that side. The procedure
> is to drop to 300 hz roofing and DSP and move the RX center 50 hz away
> from TX frequency and the VLS. I give up listening so far on the side of
> the VLS, but keep the real estate on the other side.  
> 
> It is a matter of the width out to the edge and the largest db drop per 10
> hz in the skirts thereafter. The roofing filter keeps the VLS from getting
> into the hardware AGC or pushing the DSP to the extreme.  
> 
> I have used both of these filters for years in my FT1000MP and am
> completely familiar with their shape and use in a contest. 
> 
> I have heard it said that the 200 5 pole filter will do better for picking
> out signals in a very crowded situation, perhaps so in an extremely tight
> situation. But thus far I have been able to go narrow with the 300 8 pole
> and it is the DSP handling the work there. 
> 
> At some point I would like to be able to tune the center of the DSP CW
> selectivity up/down at 25 Hz rate using RIT *WITHOUT* moving the position
> of the roofing filter relative to the band.  The point of the roofing
> filter is to reject the VLS in the next slot above and below me. Tune the
> whole thing up or down to listen to a weak station off-frequency for
> whatever reason and you let one of the VLS in under the roof.
> 
> Just the view from the other side of the river... :>)
> 
> 
> 73, Guy. 
> 
> 

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