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Author Topic: K3 CW narrow filter ringing  (Read 4562 times)
VK5DO
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Posts: 79




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« on: March 14, 2011, 07:35:22 PM »

Hi All,

Another K3 specific question for those that have them...... 

On the K3, when using a very narrow filter on CW do you get that awefull "ringing" that makes narrow filters such a joy to use?  I like to use pretty tight filtering on my IC7000 for CW but much less than about 400hz produces very pronounced ringing. 

I was looking at a few videos on You Tube of the Flex 3000 with guys setting real tight (like 50hz) filters that are totally devoid of any ringing.  I suspect that is more a feature of SDR and basically with any "normal" radio/filtering, ringing will always be an issue to some extent but is the K3 any better than others in this area?

Thanks,
Dene
VK5DO
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W8JX
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Posts: 5489




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« Reply #1 on: March 14, 2011, 08:15:29 PM »

Ringing is fairly common with analog xtal filters that are very narrow (less than 500hz) and some are worse than others. It is not a issue with IF or even AF DSP generally.  In my TS-570 and TS-480 I have a 500hz filter and when i need it even tighter I use AF DSP and can cut it real tight. K3 is IF DSP and should do nicely. Flex is basically AF DSP done in computer. 
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K0OD
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« Reply #2 on: March 14, 2011, 08:47:38 PM »

Quote
videos on You Tube of the Flex 3000 with guys setting real tight (like 50hz) filters that are totally devoid of any ringing.

I have a 5000 which displays ten CW bandpass settings down to 250, 100, 50 and even 25 Hz. (Plus Flex allows creating your own filters) But the narrowest filters require settings that compromise the radio's performance in other ways and require a pretty good computer. 100 Hz is about as narrow as mine will go. But it has a very good shape factor and without ringing.

 
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W8JX
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« Reply #3 on: March 14, 2011, 08:58:00 PM »

My TS 480 will do 50hz fine and auto tune it too and my old 570 did 80 hz this way 12 years ago so this is no Flex only or recent trick. Lot of AF/IF DSP rigs can do it without a computer. Before advent of DSP this was impractible to do effectively. 
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K0OD
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« Reply #4 on: March 15, 2011, 05:46:19 AM »

Since I've had a Flex with its ten SSB and ten CW filers I've become much less enamored with narrow filters. Even with heavy QRM, wider is sometimes better to improve audio quality. I usually use 2.7 on SSB and almost never less that 2.4.

I paid a lot for an optional narrow Kenwood SSB filter (1.8 hz?) years ago for my TS-850 and almost never used it.

Filters narrower than 200 Hz can cause distortion to high speed CW. And I don't buy the theory that ultra narrow filters make weak real-world signals easier to copy. They don't help copy weak, watery Asian signals on 80 and 160 for example.

Showy narrow filters are mostly about marketing, in my opinion.
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W8JX
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« Reply #5 on: March 15, 2011, 08:21:37 AM »

Will I do not use 1.8 khz SSB filter 100% of the time I do use it a lot. Granted there is some loss of audio quality from reduced bandwidth but it is a good trade off when QRM is present. On CW I have copied CW filters fine at 100 hz and less band passes using DSP with no loss of quality and actually I have a 270 hz filter I can use in 570 and it does not ring and plays well with CW too but I find it too narrow for Digi and use 500 instead as the "standard". If you are have trouble clearing coping a CW signal is a narrow DSP band width, you either have poor DSP, radio stability issues (as narrow bandwidth shows this more) or signal source has some stability/drift issues too. Just now on my old 570 I tuned a few CW signals on 20m, hit auto tune then selected bandwidth and dialed it down to 100 hz with no loss of quality and could even dial 80 or 50hz too but it is sounding a bit tighter below 100 hz but still quite readable. If you are having problem with narrow widths it is equipment involved not bandwidth itself.
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K0XU
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« Reply #6 on: March 15, 2011, 09:58:35 PM »

I don't notice any on my K3 cranked down to 50Hz with a 250 Hz roofing filter.

Jim K0XU
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K0OD
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« Reply #7 on: March 15, 2011, 10:27:16 PM »

CW bandwidth is a product of code speed among other things. High speed = more bandwidth. 
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WX7G
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« Reply #8 on: March 16, 2011, 08:19:58 AM »

My K3 has the 400 Hz crystal filter. Using the DSP filter below 150 Hz yields no improvement and actually exhibits a degradation in copying signals near the noise level.

I prefer the Noise Reduction setting 7-2.
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K0OD
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« Reply #9 on: March 16, 2011, 09:18:27 AM »

"Using the DSP filter below 150 Hz yields no improvement"

Meaning what, Dave?  That below 150 Hz isn't really narrower or that it's narrower but other problems kick in? 
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W8JX
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« Reply #10 on: March 16, 2011, 12:09:14 PM »

My 570 and 480 use a 500hz "rock" and AF DSP below that. Not until you get below 100 hz does it start to feel a little too tight at time. One thing tuning/zero beat is VERY critical here as you narrow bandwidth and I let radios auto tune before I tighten it up.
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WX7G
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« Reply #11 on: March 16, 2011, 12:45:55 PM »

At DSP filter bandwidths below 150 Hz, and when the S/N ratio is low, the S/N ratio does degrade. I believe this is due to noise causing the filter to ring.
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W5DC
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« Reply #12 on: March 16, 2011, 01:11:01 PM »

Whether using the K3 narrow cw filter depends on the nature of the signal.  If the signal has predominantly impulse noise, the the narrow filter will probably produce ringing.  On the other, it the input to the filter is predominantly non-impulse in character such as cw signals in a pileup, ringing may not be a problem.  I've used my K3 filter at bandwidths down to 50 Hz with useful results.

Dunc, W5DC
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W8JX
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« Reply #13 on: March 16, 2011, 04:40:54 PM »

One day radios will get advanced enough they will be able to digitally process a analogy signal of choice and ignore everything else. (I have no doubt gov has this now but outside of average consumer price range right now)
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