Thin Audio
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I have been battling a problem with my sideband adapter for the K2. The
receive audio on both sidebands (upper is much worse than lower) sounds very thin. When a station is not tuned, the received static has a tiny "shrill" quality. I used spectrogram to align the filters and the curves produced very closely resemble those depicted in N0SS instructions. Yes, I have checked that the BFO settings are appropriate to the "lowest pitch" of the BFO range. I have redone the alignments several times and still get the same result. Compared to my other rigs, the K2 is much thinner and is reminiscent of an old 6 transistor radio compared to a boom box. Even with an external speaker (A Collins 312B-3) the sound is objectionable. I aligned the CW filters in the same way and they work normally. It is fair to say that I have never been happy with the sound on sideband. I have checked the SSB adapter board for assembly errors, but have found none. It is clear that I am either making a systematic error in the alignment procedure, or there is something wrong with the adapter. Any and all thoughts would be appreciated. Fred Bongard WB6JLL _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Fred, you didn't provide any serial numbers. Things have changed a lot over
the years and some ops are picking up older K2's. If yours is not a very recent one, that may be the underlying reason. If you have a pre S/N 3000 K2, some of the problem is caused by slope in the 2nd XFIL. That's the crystal filter at the output end of the I.F. amplifier. It's a simple filter designed to cut down high frequency noise generated in the I.F. amplifier, but in the original K2 it has a significant slope that is VERY noticeable on SSB. It wasn't at all an issue when using bandwidths of 1 kHz or less, so it didn't turn up until a significant number of K2's were being used with the SSB board or in CW at wide bandwidths to listen to SSB. The SSB filter in early K2 SSB module boards sometimes had a bandwidth that was too narrow for good SSB. It was sometimes well under 2 kHz. It's virtually impossible to pass good audio through such a narrow bandwidth. It was a year or so ago when they redesigned the filter and issued upgrade kits to widen the bandwidth. Basically, it involves changing out all the xtals used in the filter and BFO. Even with the newer crystals, some ops wanted a wider bandwidth and one of our list electronic guru's, John Grebenkemper, develop a couple of mods to do that. I understand that at some point afterward, one version of his mod was incorporated into the K2 kit as shipped. You can find these mods under the Builders Resources area of the Elecraft web site (www.elecraft.com). I believe that there is, in that list, a mod to widen even the current SSB bandwidth. A lot of ops have asked why Elecraft chose such a narrow SSB bandwidth originally. They were 'shooting' for a bandwidth of 2.0 kHz when many rigs use 2.2 to 2.4 kHz. The reason lies in the K2's QRP "roots". Narrower passbands provide greater signal-to-noise ratios at the far end for a given power. The limit, as you've noted, is that intelligibility suffers if the bandwidth is too narrow. 2.0 kHz was considered the optimum tradeoff. However, some ops do not like the sound of that narrow of a filter, especially after the KPA100 amplifier became available. Ron AC7AC -----Original Message----- I have been battling a problem with my sideband adapter for the K2. The receive audio on both sidebands (upper is much worse than lower) sounds very thin. When a station is not tuned, the received static has a tiny "shrill" quality. I used spectrogram to align the filters and the curves produced very closely resemble those depicted in N0SS instructions. Yes, I have checked that the BFO settings are appropriate to the "lowest pitch" of the BFO range. I have redone the alignments several times and still get the same result. Compared to my other rigs, the K2 is much thinner and is reminiscent of an old 6 transistor radio compared to a boom box. Even with an external speaker (A Collins 312B-3) the sound is objectionable. I aligned the CW filters in the same way and they work normally. It is fair to say that I have never been happy with the sound on sideband. I have checked the SSB adapter board for assembly errors, but have found none. It is clear that I am either making a systematic error in the alignment procedure, or there is something wrong with the adapter. Any and all thoughts would be appreciated. Fred Bongard WB6JLL _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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Whups... Sorry but I meant to point out in my prior message that there's a
mod to fix the pre S/N 3000 K2's 2nd XFIL slope on the Elecraft web site as well as mods for the other things. All of the audio quality issues that have been uncovered over the past several years since the K2 was developed have been addressed and fixed either by changes to the basic K2 or by mods for the older units. It sure that if someone comes up with a new issue, there'll be a fix developed for it as well! That's one of the most talked-about sources of great satisfaction among Elecraft customers. If something can be improved, Wayne and Eric are right there helping or encouraging ops to do it. Many of the improvements are kitted for retrofit in the older rigs and they are periodically incorporated in the basic new rigs being shipped. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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