In the original build of my K2 #4168 decided that a greater SSB bandwidth
filter in the KSB2 SSB option than the normal 2.0kHz was needed. John, KI6WX
recommended to go for 2.2kHz, so that was done.
Sourced the extra capacitors needed in the UK and used 2.5mm lead spacing cer
amic plate 2% tolerance capacitors. 10 capacitors are required, 2 x 27pF and
6 x 39pF. The 2 x 100pF can be recovered from the original KSB2 kit.
The response when checked with Spectrogram was pretty flat with minimal
ripple compared to the original K2 filter. The bandwidth came out in my case
with
the components used at certainly greater than 2.2kHz, though less than
2.4kHz, so this is where the 2.3kHz figure may be accurate for some builders.
Perhaps other K2 builders could comment on their results?
I did a comparison against my main station receiver the JRC NRD-515 which
has a nominal 2.4kHz bandwidth, Kokusai 455kHz mechanical filter. The results
of the two receivers were very comparable in the Spectrogram traces with the
NRD-515 coming out as slightly wider than the modified K2. This puts the K2 in
good light as I would rate the NRD-515 against most receivers on the market
despite it now being manufactured 23 years back.
For the K2 owners that use SSB TX, I find good results with an Altec Lansing
AHS-201 computer headset when used with the K2. This is a cheap PC headset
with a noise cancelling electret boom microphone and a single earpiece
probably costing about $10 in the USA. The operating voltage for the microphone
can
be supplied by the K2 or as mine was originally for a handsfree mobile use
with another radio, a single AA 1.5V cell provides the necessary power. A PTT
switch can be added as a footswitch or as in my case with the small plastic
battery box.
Seems to work very well and particularly works with my voice on SSB. Took 30
years trying different microphones on SSB before I hit the jackpot with
electret microphones. The North American voice is much more suited to SSB it
would seem that the European one for use with standard microphones.
Bob, G3VVT
K2 #4168
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