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Author Topic: Sidetone Frequency  (Read 11478 times)
K3STX
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Posts: 983




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« Reply #30 on: November 25, 2010, 06:17:41 PM »

I use a 400 Hz sidetone, I find it most useful to listen with this low frequency on 80 and 160. And maybe I need a new rig, all I have is a TS-850S with the stock Kenwood 500 Hz filters. With really weak signals I mostly hear hiss with both 50 Hz filters in, sometimes I have to listen with the 2.7 kHz "filters" just to keep the hiss down.

Oh well... Only 15 more years till my last kid is done with college. By then they will be on the K6.

paul
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N3QE
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Posts: 2223




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« Reply #31 on: November 26, 2010, 06:43:06 AM »

Filters with less than 100Hz bandwidth do improve the SNR within the critical band.
Filters with more than 100Hz bandwidth do not improve the SNR within the critical band.

And as I said, this is only true for signals that are only masked by pure noise (i.e. band-filtered white noise).

I've been a CW op for 32 years now. So maybe a newbie compared to some. But I'm going to repeat my opinions, backed up by my experience over the decades.

I've tried using narrow filters (meaning less than 300Hz). They induce a certain mental state where pretty soon every static crash sounds like a dit or a dah. This is not an immediate thing, but sets in after operating for a while.

Why does this happen? Hit a 100 Hz wide filter with a static crash that is 50 ms long. A static crash is by definition a wide bandwidth signal with a lot of energy at a broad range of frequencies. Thanks to the filter, only the portion of the static crash in that 100 Hz window gets through. If there's energy in that window it comes through, and when it comes through it's nearly indistinguishable from a real dit that's 50 ms long, because the window is so narrow.

You know how long a dit is at 24 WPM? 50 ms.

You know what the sideband bandwidth of a dit at 24 WPM is? For typical keying rise and fall times of commercial rigs (2.5 ms) the sidebands go out +/- 100 Hz for a an actual bandwidth of 200Hz; due to poor keying shape of typical commercial rigs the actual occupied bandwidth of a dit at 24 WPM will be more than 400 Hz usually. That means that a 100 Hz wide filter is actually throwing away the "sharpness" of the beginning and end of the dit - features that my ears and brain might otherwise use to distinguish a real dit from a static crash, but which are simply removed by using a ridiculously narrow (100 Hz) filter.

With a much wider filter, assuming no interfering carriers, the same static crash conditions do not sound like a dit. Because I hear the static crash frequencies outside the same frequency of the morse dit, and I immediately know it's a static crash, not a dit. I'm using the BESP (Brain Ear Signal Processor) in my head to make that determination. And the fact that energy outside a ridiculously narrow bandwidth is available to do that.

The psycho-acoustic effect of using a narrow bandwidth filter for extended listening periods is even more nefarious. Switching to a narrow filter for a little while, because of interfering carriers nearby, is one thing. But I find that listening to narrow bandwidths for extended periods of time induces a strange kind of audio psychosis, where the restricted bandwidth just drives me nuts.

Do I ever use the narrow bandpass filters? Yeah, but I do not prefer them. I abhor them. They are there to get rid of nearby interfering carriers that cannot be removed with a simple notch. (Incidentally, narrow bandwidth notches, I do not find nearly so objectionable, especially when used with a nice wide filter. Yeah, the keyclicks from the interference comes through, and it's annoying to hear how awful so many CW transmitters sound especially during a DX contest, but the long term acoustic psychosis in me is not triggered by them.)

IME some filters are more appropriate for narrow use than others. "Brick wall" filters are the worst because of poor time domain response. Gaussian filters (which have gently sloping sides) do a lot better. I have homebrewed Gaussian crystal filters and Gaussian audio filters and find them far preferable to brick wall filters. What is a shame, is that for decades now the ham radio community has treated filter shape factor as something to optimize in the direction of brick wall, and away from gently sloping sides. This is a huge disservice to folks who buy commercial rigs built for specsmanship rather than actual usability. If you can get a nice 500 Hz Gaussian "roofing filter" for you fancy new rig, you are in for a world of joy when it comes to CW operating. But AFAIK I can't buy them, so I build them.

I know, I'm bucking the trend. Everyone else says that you need narrower, narrower, narrower filters, and they need to be more like a brick wall. I'm saying the opposite.

Tim.
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K0OD
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Posts: 2557




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« Reply #32 on: November 28, 2010, 05:35:01 PM »

I'm with N3QE. My Flex-5000A has oodles of adjustable CW filters and narrowing the passband doesn't make ultra-weak signals more copyable, at least with my brain, and my old ears.  This subject came up last year and several of the engineers agreed that real radios and real signals in static, and cerebral DSP don't behave like textbook theory.

Timely subject for me: Flex's default CW offset is 600 Hz which is what I had used until this past weekend (CQWW CW) when I switched to 550 Hz.  I had used 700 Hz with other radios when I was younger. Thought 700 was once considered the norm. Perhaps aging has something to do with it.

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N4MJG
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Posts: 506


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« Reply #33 on: November 28, 2010, 07:13:20 PM »

Guys,


There is one problem for me is my ft-847  does not have narrow filters since 2001 brought it new, i was tech back in 2001. it hard to find the narrow filter for this ft-847 but i did found irad cw filters ! anyway my pitch is round 750hz.   Grin



73
Jackie
N4MJG
WWW.N4MJG.COM

-. ....- -- .--- --.
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WB2WIK
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Posts: 20603




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« Reply #34 on: November 29, 2010, 08:51:32 AM »

I use a 400 Hz sidetone, I find it most useful to listen with this low frequency on 80 and 160. And maybe I need a new rig, all I have is a TS-850S with the stock Kenwood 500 Hz filters. With really weak signals I mostly hear hiss with both 50 Hz filters in, sometimes I have to listen with the 2.7 kHz "filters" just to keep the hiss down.


My TS-850S doesn't behave that way.  With both 500 Hz filters in, there's more loss in the IF signal path, so I turn the volume up; however weak signals don't go away, they actually become clearer and easier to copy, and there's less hiss (not more).

I suspect your rig or filters (or combination thereof) has some sort of problem.  Could be it needs critical IF alignment (8.83 MHz and 455 kHz) to assure stuff's all peaked where it needs to be in consideration of the very narrow bandwidth and added loss of the CW filters; this is just a guess, but from your description, something's not quite right. 
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K3STX
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Posts: 983




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« Reply #35 on: November 29, 2010, 07:49:41 PM »


I suspect your rig or filters (or combination thereof) has some sort of problem.  Could be it needs critical IF alignment (8.83 MHz and 455 kHz) to assure stuff's all peaked where it needs to be in consideration of the very narrow bandwidth and added loss of the CW filters; this is just a guess, but from your description, something's not quite right. 

I got this rig used recently, have no idea if it has ever been looked at. Maybe I should do this. We used to have a local Kenwood tech here, now I guess it means mailing to AVVID.

paul
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WB2WIK
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« Reply #36 on: November 30, 2010, 08:30:20 AM »


I suspect your rig or filters (or combination thereof) has some sort of problem.  Could be it needs critical IF alignment (8.83 MHz and 455 kHz) to assure stuff's all peaked where it needs to be in consideration of the very narrow bandwidth and added loss of the CW filters; this is just a guess, but from your description, something's not quite right. 

I got this rig used recently, have no idea if it has ever been looked at. Maybe I should do this. We used to have a local Kenwood tech here, now I guess it means mailing to AVVID.

paul

I'd say if it doesn't bother you, don't have it serviced yet.  Wait until something really goes wrong, and some day something probably will (these are all getting old!), and have it serviced then, and aligned coincidentally. Wink
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KA1VF
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Posts: 35




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« Reply #37 on: December 02, 2010, 08:42:11 AM »

A caveat that seems to be missing from this 'sidetone' discussion is the ramifications of keying on the LSB rather than the USB.

Last weekend, I worked the CQWW CW contest with my rig's (Yaesu FT-450AT) CW defaults which are USB with 700 Hz offset.

   
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N3QE
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Posts: 2223




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« Reply #38 on: December 02, 2010, 09:44:30 AM »

A caveat that seems to be missing from this 'sidetone' discussion is the ramifications of keying on the LSB rather than the USB.

Last weekend, I worked the CQWW CW contest with my rig's (Yaesu FT-450AT) CW defaults which are USB with 700 Hz offset.

I don't see the issue. Anyone can listen with their BFO on either side of the carrier, to their operating preference. And being able to choose above or below, on the fly, makes more efficient use of the band when QRM comes up.

Now, if ham CW were channelized the way some believe it is, then BFO placement may be an issue depending on getting the "right number" on the radio's frequency display, but that's a nonstarter because ham CW operation has never been channelized that way. Besides don't most modern radios show the transmit carrier frequency when in CW mode? (I could be wrong on that, all my "new" stuff is homebrew.) Back in the 60's a lot of SSB radios, in CW mode, would read 700 Hz above in one sideband and 700 Hz below in the other sideband but we've moved beyond that, right?

Tim.
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KA1VF
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Posts: 35




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« Reply #39 on: December 02, 2010, 07:40:29 PM »

  I'm keying on USB with a 700 Hz offset and a 500 Hz filter, and you're keying on LSB with a 400 Hz offset and a 270 Hz filter.
 
  Discussion question: Won't we have alot of trouble zero beating ('spotting') each other before we can have a quality QSO?

 
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WB2WIK
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« Reply #40 on: December 03, 2010, 09:07:48 AM »

Not normally, no.

The dial indicates the carrier frequency.  If you tune someone in to the same pitch as your sidetone in most rigs, they'll hear you just as you hear them.

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N3QE
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« Reply #41 on: December 03, 2010, 05:41:42 PM »

> Discussion question: Won't we have alot of trouble zero beating ('spotting') each other before we can have a quality QSO?

If someone insists on using a narrow filter, they've always got RIT.

That doesn't mean that there aren't folks out there with 25Hz filters who don't know how to use RIT. I've met a couple. But any reasonable ham will be accomodating and realize that they can carry on the QSO just with a slight tweak of the RIT knob. When I was younger and operation on the novice bands was crystalized "listening up and down" was perfectly standard, and I'm not talking 200 Hz up, I'm talking many many kHz up. To expect a modern op with a modern radio to not be able to accomdate a few hundred Hz split in carrier frequencies, is expecting way too little.
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