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. > > -- View this message in context: http://n2.nabble.com/Hearing-the-effect-of-narrower-roofing-filter-tp470635p795593.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
