Ray,
You would have to use a noise generator for a proper test - the
atmospheric noise varies from band to band and from antenna to antenna.
On the bands above 17 meters, the K2 local oscillator uses low side
injection as opposed to high side injection on 17 meters and below.
That means that the audio passband for 15m USB (and 12 and 10 meters
should be the same as LSB on bands below 15 meters. There will be no
difference.
If you have doubts, use a wideband noise generator (Elecraft N-Gen) and
look at the audio passband on an audio spectrum analyzer (like
Spectrogram or SpectrumLab) and you should see the same audio passband
shape on 40 meter LSB as you do on 15 meter USB.
The bandpass filters are not likely to make a lot of difference unless
they are severely mis-tuned. For the best response from the bandpass
filters, tune them in transmit mode for peak output at 100 kHz above the
low frequency end of the band for 40 through 12 meters, on 10 meters
tune them at 26.400 MHz and for 80 use 3750 kHz and if you have 160
meters, start at 1850 kHz and you may have to find a compromise setting
between 160 and 80 meters since the inductors are shared and the
capacitor are fixed (but that bandpass is quite broadbanded abd that
compromise works just fine).
73,
Don W3FPR
On 7/24/2013 6:05 PM, Ray Collins wrote:
I have noticed that as I change frequency bands on my K2 in SSB mode, the audio
noise level changes in frequency content. On the five lower bands (3.5 to 18.2
MHz), the noise sounds typical for a 2.2 KHz audio bandwidth but on the three
higher bands (21.0 to 28.8 MHz) it is predominantly high frequency with greatly
reduced low frequency content.
The appropriate sideband is correctly selected for each band, receiver
sensitivity appears to be well within specification on all bands and the set
works perfectly in all other respects. Could the band pass filters for the top
three bands require adjustment? If anyone can explain why this is happening
and suggest a fix (if one is actually necessary), it would be greatly
appreciated
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