KSB2 - 1.9 kHz mods and wish list

[Bill Coleman-2]

This last week, I made the KI6WX modifications to my filter for the
"1.9 kHz" passband. I don't know of anyone else who has done this mod,
although plenty have made the 2.2 and 2.5 kHz changes, and the 2.2
design is now standard. I thought the list might want to read a report.

Since my KSB2 had the original caps, it only required changing four
caps to get the 1.9 filter.

The change was pretty quick. The hardest part of this mod was
desoldering the caps. I don't have a Hakko, so this was a pretty ugly
process.

Slapped the board back in an ran a quick CAL FIL using a spectrum
analyser on my Mac. The LSB filter looked fine, the USB filter only
needed to be knocked back one notch.

This is a very minimal change. According to the figures published by
KI6WX, the 1.9 filter is pretty much the same bandwidth as the
original, but with slightly less bandpass ripple. I found this to be
true. There's visibly less ripple, but it is certainly not flat.

After the mod, I made a few contacts and got some audio reports. One
fellow told me not to change anything -- it sounded good to him with my
HC-4 mic element. I then ran the ARRL SS Phone contest and made 855
contacts. (About 835 of which were made on the K2/100!)

Doing SS Phone reminded me of some of the K2's warts with SSB. The
K2/100 is such a fantastic CW radio, it's shortcomings on SSB are
annoying:

1) Filter. I'm surprised some third party hasn't come up with a
monolithic filter for the K2. It really needs one. The existing filter
is fine for casual use, but it could use much steeper skirts for
contests. And a flatter passband wouldn't hurt either.

It would also be very nice to have a choice of filter(s). The 1.9
filter is great in contests, but I'm sure the fidelity suffers a bit
for ragchewing.

2) VOX Sensitivity. In contests, I have a one-message voice keyer that
runs in-line with my mic. Sometimes, the K2 VOX sensitivity gets really
wonky. While speaking, I'll trip it, but the voice keyer will not. The
weird thing was I could hit the foot switch and then the voice keyer,
and it would start transmitting, and then the VOX would work even if I
let go of the foot switch while the message was still playing. But it
wouldn't start transmitting without tapping the foot switch. This
condition persisted for a long time, and only went away when I cycled
the power on the K2.

The worst part is, there's no way to crank up the VOX sensitivity. I
replaced the R14 resistor with a 3.9k, and this helped a bit.

3) Mic Sensitivity. I haven't done the KI6WX gain mods to the KSB2, but
I'm considering it. The HC-4 just barely drives the K2 to full output.
Seems like a mic pre-amp is probably a good idea.

4) VOX Delay and Switch. I bought the firmware change with the 0.2 vox
hold, but I end up using 0.4 anyway, because of the sensitivity
problem. It would be nice to have an adjustable delay, so one could
make the delay just short enough to match the cadence of one's voice
without it being too long.

One problem is that turning the VOX off and one takes multiple key
holds. While I'm playing contests, my kids sometimes wander into the
shack to ask me questions. Sometimes I don't hold one of the keys long
enough and then end up transmitting accidentally. I think I could
prefer a menu item to select the VOX delay, and just have the mode-hold
toggle the VOX on and off.

It certainly would be nice to see these features in an upgrade KSB2.
Here's to hoping....

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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