Thin Audio

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Thin Audio

Fred Bongard
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

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RE: Thin Audio

Ron D'Eau Claire-2
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


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RE: Thin Audio

Ron D'Eau Claire-2
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



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