Posted by
Ron D'Eau Claire-2 on
Aug 14, 2006; 5:02pm
URL: http://elecraft.85.s1.nabble.com/Up-conversion-tp392867p392874.html
Two things conspired to cause trouble with early K2 SSB. Steve touched on
one of them about variations in crystals.
The original K2 SSB filter was purposely designed to be as narrow as
possible to give the signal more "punch", especially for weak-signal/QRP
operation. The narrower the bandwidth of a signal at a given power, the
louder it sounds at the receiving end. So the SSB filter was designed to be
just a tad over 2 kHz. That's about the minimum for good "communications
quality" SSB.
As Steve, W2MY observed, the variations in crystals from the manufacture
meant there was a wide variation in SSB filter bandwidth. For example, mine
was barely 1800 Hz wide at 6 dB down! There was no way I could get
good-sounding SSB out of it.
Several years ago Elecraft changed the filter design for a wider bandwidth
*and* employed more consistent crystals in the kit so there was less
variation from rig to rig. That seemed to put an end to all issues with the
filter. When I put new crystals into the filter, I opted for the wide
bandwidth mod since my use of SSB is very casual anyway. That fixed the
audio quality problem.
As Don pointed out, it is true that the K2 requires a fairly high output
microphone. That's especially true on 10 meters where the transmitter has
the least overall gain, so low audio will show up as less-than-full output
if you're trying to run the full 10 watts PEP with a QRP K2 or 100 watts PEP
with a K2/100.
Ron AC7AC
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