[Elecraft] Re: Question on Purchase of K2

[wayne burdick]

On Feb 21, 2005, at 11:39 PM, frank wrote:

> I'm getting close to order a K2 but I have a few questions.
> The K2 would be for CW operation only.
> Like many others, I prefer to tune the band using wide bandpass of
> over 2khz and only use narrow CW filter operation when band
> conditions require it.  My understanding is that if you equip the K2
> with the SSB module, that you can use the SSB filter on CW and that
> works better than operating the CW filter on wide setting. Is that
> true?  If so it would be worth the extra cost of the ssb option.
>
> I have decided not to order the DSP filter but perhaps the passive
> audio filter.   The passive audio filter appears to be set up for
> 80hz bandwidth which is way too narrow for my liking.    Is there
> any easy way to change that for 250hz bandwidth?   If not I'll have
> to go with an outboard audio filter.
>

Hi Frank,

The SSB filter is much more pleasant to use than the CW filter set for 
a wide bandwidth. The SSB filter has a flat passband, whereas the CW 
filter, being varactor controlled, develops a lot of ripple by the time 
you widen it out. We experimented with variations on the filter 
topology before releasing the K2 to production, but it was getting too 
complex.

A 2 kHz filter is especially useful on quiet bands or if you're working 
a contest where you may get called up/down significantly from your 
carrier frequency. I use it much of the time. And heck, you might just 
want to listen to AM or SSB sometime :)

As for the audio filter: you can change the components in the op-amp 
circuit to make it more like 250 Hz if you prefer. But the time when 
the 80 Hz filter is really useful is when you're trying to pick a weak 
one out of atmospheric noise and/or nearby QRM. Most of the time you'll 
probably just leave the audio filter in its OFF position. But that 
still keeps in-circuit the KAF2's passive (L-C) low-pass filter, which 
removes the small amount of residual hiss from the product detector. It 
also improves roll-off of high-pitched QRM, and thus enhances the 
ultimate rejection of the I.F. filters. It's very effective for those 
who sometimes use headphones with the rig.

The DSP filter is quite flexible, and adds stochastic noise reduction 
as well as notch filtering. But if you don't live in a very noisy area 
or use SSB, you may find the KAF2 just as useful (and at lower cost).

I hope you enjoy using the rig if you do decide to buy one. Eric and I 
are both serious CW ops, and we designed the rig from the ground up to 
be a great home/portable CW rig. (Keying is state-of-the art with the 
latest circuit changes, too.)

As the principle designer of the K2, I'd be happy to answer any further 
technical questions.

73,
Wayne Burdick
N6KR


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