[Elecraft] K1 kit suggestions? Response Part 2

[Mike Morrow]

Gil advised:

> If I was building another one, I would installed the capacitor required
> for the 80m filter board, so if you ever want to build a board with that
> band, you wouldn't have to remove the bottom cover again.

That is RF PCB C78.  The same advice is appropriate for RF PCB RFC8.
But...these parts are **only** supplied with an 80m two-band KFL1-2.
Neither are supplied with the four-band KFL1-4, which does not cover
80m.

> I also did change a capacitor to speed up AGC, can't remember which,
> but it should be easy to find.

It **is** easy to find...see the message I posted a few hours ago.  That's
RF PCB C31.  The most commonly used non-stock value is 1 uF, but people
have been happy with 0.47 uF and even smaller.  The stock 2.2 uF is just
terrible.

> I highly recommend using Spectrogram or even Fldigi to center the filters.

That is a nice approach, but only for adjusting the value of product detector
tuning capacitor RF PCB C20.  It is a waste of effort to use those techniques
to set **anything** on the filter board itself.  If one does that, the
immediate result is very precise adjustment of the filter board capacitors
for optimal received signal performance.  But...these same circuits are used
in transmission mode.  If left without further adjustment, in transmission
mode one will likely have little or no transmitter output.  The adjustments
of the capacitors of the KFL1-4 (or inductors of the KFL1-2) are far far far
more critical for transmit than for receive.  That's why the manual makes
**all** of the final adjustments of filter board variable reactances in
**transmit** mode.  So...that will upset every one of those fine adjustments
that had been made earlier in receive mode during the alignment process.

It is unnecessary to use anything other than the simple straightforward
method that is described in the K1 manual, no part of which mentions the
use of Spectrogram or the like. 

> I did opt for the 150KHz bandwidth, works fine, but it is a bit touchy.

Well, VFO span...not bandwidth.  It's touchy because the VFO pot has almost
no resistance to rotation.  When fingers are removed from the knob, it is
difficult to avoid some slight angular displacement of the knob.  I like
the 150 kHz VFO span option (one will actually get about 170 kHz), for
which 120 pF is used as RF PCB C2.  That'll allow coverage of the Morse
activity that is still common above 7.1 MHz, as well as allowing copy of
10 MHz WWV on the 30m band.  I placed some hand-cut thin felt washers
between the VFO knob's back and the front panel to give some needed light
rotational resistance.  The VFO pot system is fairly linear...there will
be about 17 kHz per complete turn of the VFO knob.

The K1 receiver operates in LSB mode, given currently-supplied filter board
heterodyne crystal frequencies.  A 170 kHz VFO span allows the possibility
of cross-mode contacts on 40m.  LSB is intelligible when the K1 is set for
its maximum IF bandwidth of about 850 Hz, but it's not going to be hi-fi!

The KFL1-4 can cover either 17m or 15m.  The 17m band is a fine band, but
it no way matches 15m during the solar cycle maximum.  When open, 15m is
the best QRP band ever, IMHO.

The K1 is a mature product, with its first deliveries in Fall 2000.  All
of the hardware issues were resolved more than a decade ago.  The
significant errors in the manuals were removed a few years ago.  There's
not too much that can go wrong as long as the K1 manual is followed
closely and exactly (note the proper toroid turns counting described
on page 14).  There's not even an errata sheet for K1 manual revision I!

73,
Mike / KK5F