K1 Bandwidth Question

[J S-17]

I built a K1 in 2004 and sold it.  I'm thinking about building another
one, but the K1 I had did not go above about 7075 kHz on 40 meters.
I'd like the band coverage to be up to about 7120 kHz.  As I recall,
the only way to do that is to replace a capacitor, I think it was, but
at considerable compromise to selectivity.  The other question:  has a
KAF2 audio filter mod or something like it ever been considered for
the K1?

Jeff
K6ATT
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Mike Morrow-3]

Jeff wrote:

>I built a K1 in 2004 and sold it.  I'm thinking about building another
>one, but the K1 I had did not go above about 7075 kHz on 40 meters.
>I'd like the band coverage to be up to about 7120 kHz.  As I recall,
>the only way to do that is to replace a capacitor, I think it was, but
>at considerable compromise to selectivity.

The K1 kit comes with two capacitors that may be installed at RF-C120 to give either about a 80 kHz or a 170 kHz VFO span.  The choice has absolutely *NO* effect on the selectivity of the K1, which is unchanged and excellent regardless of VFO span.

Due to the extreme lack of resistance to motion of the VFO pot shaft, some find that the 170 kHz span makes it difficult to remove their fingers from the VFO knob without disturbing the setting (which they would also do with the 80 kHz span option, only the effect wouldn't be as noticable).  This very trivial problem is easily solved by putting some thin felt material between the panel and the back of the VFO knob.

With respect to K1 spurious signal rejection at the receiver front-end, the four-band filter board is better than the two-band filter board.  The elliptical low-pass filters of the four-band board are far sharper and deeper than the simple filters on the two-band board.

>...has a KAF2 audio filter mod or something like it ever been
>considered for the K1?

It wouldn't seem to provide much advantage.  The bandwidth of the four-pole crystal IF filter may be adjusted in three steps from about 200 to 850 kHz.  The selectivity as designed is outstanding.

Mike / KK5F
K1 #175 since 11/2000
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Rick Dettinger-2]

> It wouldn't seem to provide much advantage.  The bandwidth of the
four-pole crystal IF filter may be adjusted in three steps from about 200 to
850 kHz.  The selectivity as designed is outstanding.
>
> Mike / KK5F
> K1 #175 since 11/2000

====================================
 I usually use an outboard audio filter when operating at home.  I agree
that it is not needed for selectivity  but it makes the sidetone sound like
my K2 and I enjoy a clean CW note.  I think one problem with a simple low
pass filter is that the K1 has a wide range of possible sidetone pitch and a
cutoff frequency that would help someone who uses a low pitch as I do would
not pass a high one.  Thus, filters would need to be adjustable or custom
designed for the desired pitch.
Rick Dettinger
K7MW

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com