Re: [digitalradio] Re: narrow filters/PSK
Patricia Gibbons wrote: Yes, I have MIXW, with a tigertronics SignaLinkUSB interface, connected to a Yaesu FT897D .. In digital mode, I can select the 500 Hz CW filter, then using the IF shift, I move the IF passband so that it is centered on the signal being received .. generally when channel center is between 1000 hz and 1500 Hz... without the IF shift / passband tuning turned on, I find that the passband of the CW filter is centered within the SSB channel, i.e. centered on 1500 hz on the waterfall display .. works fairly well .. Elaine / WA6UBE .. The center frequency of the FT-897 (all versions, if I am not mistaken) is 1000hz. In digi mode, if you use your 500hz filter, you should see on the waterfall a narrowing of the passband corridor centered on 1000hz. The corridor will be roughly 500 hz wide. You do not need to mess with the IF shift to center the signal. Put another way, you want to tune a signal so that it is centered on 1000hz. If you are using CAT control, the best way to do this is to click onto the signal on the waterfall, and then use the ALIGN: 1000 macro to align the selected signal with the 1000hz spot. I find it convenient to have a MixW indicator at 1000Hz. In this way you achieve maximum benefit from the narrow IF filter. The IF shift command can then be used to filter out adjacent signals that are inside the 500hz receive passband of the radio. de Roger W6VZV
Re: [digitalradio] Re: narrow filters/PSK
I use DXLabs WinWarbler at this end, and since I posted that original question I've added both the 500 Hz and 250 Hz CW filters to my IC-746. It is amazing for PSK and RTTY. Once I get the signal within the passband - easy enough in WW - I just hit the narrow filter and almost any QRM is gone. I get a little bit of ringing with the 250 Hz filter, but the signal decodes perfectly, which is the only end result I was trying for. Wish I'd thought of trying that sooner! 73 Dave KB3MOW Patricia Gibbons wrote: Yes, I have MIXW, with a tigertronics SignaLinkUSB interface, connected to a Yaesu FT897D .. In digital mode, I can select the 500 Hz CW filter, then using the IF shift, I move the IF passband so that it is centered on the signal being received .. generally when channel center is between 1000 hz and 1500 Hz... without the IF shift / passband tuning turned on, I find that the passband of the CW filter is centered within the SSB channel, i.e. centered on 1500 hz on the waterfall display .. works fairly well .. Elaine / WA6UBE .. --- In digitalradio@yahoogroups.com mailto:digitalradio%40yahoogroups.com, Dave [EMAIL PROTECTED] wrote: Has anyone tried using either a 250 Hz or 500 Hz filter for PSK31 reception? My Icom IC-746 (non-Pro) has no filters installed, and is wide as a barn door on USB for PSK31. I wondered if either of these filters would help, or would they be too narrow? The pass-band shift does a fair job of eliminating QRM from one side or the other of the selected frequency, but when there are two very strong signals within 2 Khz on each side at the same time, they just aren't effective on both. Any input appreciated! Thanks in advance es 73 Dave KB3MOW No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.446 / Virus Database: 269.0.0/751 - Release Date: 4/7/2007 10:57 PM
[digitalradio] Re: narrow filters/PSK
Yes, I have MIXW, with a tigertronics SignaLinkUSB interface, connected to a Yaesu FT897D .. In digital mode, I can select the 500 Hz CW filter, then using the IF shift, I move the IF passband so that it is centered on the signal being received .. generally when channel center is between 1000 hz and 1500 Hz... without the IF shift / passband tuning turned on, I find that the passband of the CW filter is centered within the SSB channel, i.e. centered on 1500 hz on the waterfall display .. works fairly well .. Elaine / WA6UBE .. --- In digitalradio@yahoogroups.com, Dave [EMAIL PROTECTED] wrote: Has anyone tried using either a 250 Hz or 500 Hz filter for PSK31 reception? My Icom IC-746 (non-Pro) has no filters installed, and is wide as a barn door on USB for PSK31. I wondered if either of these filters would help, or would they be too narrow? The pass-band shift does a fair job of eliminating QRM from one side or the other of the selected frequency, but when there are two very strong signals within 2 Khz on each side at the same time, they just aren't effective on both. Any input appreciated! Thanks in advance es 73 Dave KB3MOW
[digitalradio] Re: narrow filters/PSK
The problem is with your receiver design, which was designed for SSB and CW using AGC to keep the audio output level more or less constant with RF input and prevent blasting by strong signals when listening to weak signals. It is not necessary to listen to digital modes, since they are basically visual modes. I removed the AGC in the latest production run of the PSK20 so there is no AGC capture or overload over an input range of about 60 dB. One can argue that a 60 dB dynamic range is not enough, but I have not yet encountered a signal that overloaded the PSK-20 or the soundcard, but I am sure I would during Field Day with transmitters nearby. However, for typical operating, there is no overload problem, and no AGC capture either. The gain of the IF stage was compensated for by using more gain in the audio chain. This would not work with the typical receiver designed for SSB and CW, because the gain needs to be in the IF for AGC action, and not as much in the audio as in the PSK-20. As has been mentioned, disabling the AGC is going to result in overdriving the final IF amplifiers to distortion, so that is not a solution. The only solution for current receivers is narrow filtering (when needed), but if a signal gets within the IF passband of the narrow filter it is going to capture the AGC anyway unless careful tuning, or passband tuning, or IF shift, can move the strong signal and dump it off the filter slope and still copy the weak signal. In any event, there is no substitute for a narrow filter of some kind in such situations, but it is usually possible to operate most of the time with the SSB filter as most of you already know. Perhaps some day the other receiver manufacturers will take digital modes into consideration in their receiver design. I have read that a dual-loop AGC system helps prevent AGC capture, but I have not tried it. The reason that some people have no problem with AGC capture and others do is that the receivers and antenna gains are not the same for everyone, so everyone is right! ;-) 73, Skip KH6TY - Original Message - From: digitalradio@yahoogroups.com To: digitalradio@yahoogroups.com Sent: Thursday, March 08, 2007 8:39 AM Subject: [digitalradio] Digest Number 2284 There are 18 messages in this issue. Topics in this digest: 1a. Re: narrow filters/PSK From: Roger J. Buffington 1b. Re: narrow filters/PSK From: John Bradley 1c. Re: narrow filters/PSK From: Dave Corio 1d. Re: narrow filters/PSK From: Roger J. Buffington 1e. Re: narrow filters/PSK From: Roger J. Buffington 1f. Re: narrow filters/PSK From: Danny Douglas 1g. Re: narrow filters/PSK From: Roger J. Buffington 1h. Re: narrow filters/PSK From: kv9u 1i. Re: narrow filters/PSK From: Rein Couperus 2a. Re: 3580kHz-3600kHz Freq Coordination Info From: Roger J. Buffington 2b. Re: 3580kHz-3600kHz Freq Coordination Info From: kv9u 3a. Re: Narrow? From: expeditionradio 3b. Re: Narrow? From: Danny Douglas 3c. Re: Narrow? From: expeditionradio 3d. Re: Narrow? From: Andrew O'Brien 3e. Re: Narrow? From: Danny Douglas 3f. Re[2]: [digitalradio] Re: Narrow? From: Flavio Padovani 4. Re: 3580kHz-3600kHz Freq Coordination Info From: Box SisteenHundred Messages 1a. Re: narrow filters/PSK Posted by: Roger J. Buffington [EMAIL PROTECTED] w6vzv Date: Wed Mar 7, 2007 6:05 pm ((PST)) Rein Couperus wrote: We generally use 300 Hz filters for PSK125 and they are too wide. There is no substitute for good narrow Xtal filters. I don't understand how you can try to work PSK31 (50 Hz bandwidth) with a 2.7 kHz filter. That is against all logic (and math). We recommand using the narrowest filters you can get for pskmail. That is the only way to fight Pactor QRM. It helps to use the passband shift and use the sweet spot of the rig at 1500 Hz (we use an Icom 756). Our PI4TUE server has good performance with that, provided you get the filter as narrow as possible (this is for PSK125, which is 4x the bandwidth of PSK31...). A 250 Hz Xtal filter is wide enough for PSK125. 73, Rein EA/PA0R/P Rein, you are right as rain! :-) Most Yaesu rigs have a digital passband center freq of 1000hz, but otherwise everything you say above is right on the money. de Roger W6VZV Messages in this topic (22) 1b. Re: narrow filters/PSK Posted by: John Bradley [EMAIL PROTECTED] ve5mu_sk Date: Wed Mar 7, 2007 6:16 pm ((PST)) using my TS480SAT with both CW filters, can get really narrow on PSK and still copy. don't know much about the IC746. can you menu select cw filters for ssb(digital) reception on USB? or do they only work in CW? John VE5MU - Original Message - From: Dave To: digitalradio@yahoogroups.com Sent: Wednesday, March 07, 2007 12:42
[digitalradio] Re: narrow filters/PSK
Well, You are all correct... as usual it depends; in this case it depends on mode, band and operating style. If I were, for example, using the panoramic type operation to look for a snap-shot of what was going on in cw, rtty or psk modes using Multipsk, I would opt for a fairly wide open filter of 3000 Hzif I then started a qso I would drop in a filter of as narrow as possible for the given mode. For some modes this is obviously not an option (of yet) as one is not decoding, say Olivia, on a panoramic waterfall (visual ID's using CMT Hell excluded as are RS ID's). I find the more narrow than stock filters are the reason I use the IC-746 Pro over my IC-718; but milage varies from person to person. If all I was to operate was 6 meters, using most any digitial mode, there would be little need for a more narrow than SBB filter as there is (sadly) no qrm. On the other hand, using a digital mode on 80 in the evening without a more narrow filter would make things even more miserable. 73 Bill N9DSj --- In digitalradio@yahoogroups.com, Andrew O'Brien [EMAIL PROTECTED] wrote: I agee with Danny and don't quite get what Leigh is saying. Dave's question is an interesting one because with my 3-week old DSP capable rig I, have been experimenting with the issue Dave raised. I have the ability to go down to 50 Hz IF-DSP filtering , but to be honest I find the digital bands to be so sparsely populated that I have not needed to use th filtering tha much. I'm waiting for a big contest to test this further. With regard to what Leigh is saying, I have been anxious to find out if my variable AGC and/or DSP filtering offer any significant improvement over the infamous strong PSK signal 'desenses' other signals in waterfall issue. With my admittedly little playing around, I have not found the AGC settings to make that much difference. I just noticed a strong PSK31 signal way out at the 1700 Hz mark on my waterfall. When he transmits my Multipsk waterfall darkens considerably. Turning a fitter on , in this case 1000Hz, eliminates the strong signal at 1700 and the waterfall at the lower end returns to normal. I still have not figured out how to best center on the remaining waterfall with software commands to center on 1000 or 1500 Hz, since these commands center you to parts of the band that you may have filtered out. Still need to find time to practice more. I guess I need filter out the strong signals, shift the remainder of the waterfall so that it is centered on 1000 Hz an then use align or center macros. Sounds like work though. Dave, I think 500 Hz should be all you need for all but the most unusual situations.
