[Elecraft] K1 SSB?

[Wayne Burdick]

giuliano wrote:

> i have finally modified  my K1 transceiver #1523.
> Now it work very well also on SSB (reception and trasmission).


Hi Giuliano,

I can't get to your site to look at your modifications, but it sounds
interesting. Congratulations on your initial success with such a fundamental
change to your K1.

Modifying the K1 for SSB use while preserving performance and meeting FCC
requiremenets would not be a small undertaking. It would almost certainly
require modifications well beyond what I think you've mentioned so far. So I
have a few questions, which may be answered already on your web page:

- Did you linearize the final amplifier? It is biased class C, which cannot be
used for SSB operation. It must be biased class AB or at least class B. The
lower-level TX stages must be operating class A, or close to it, or they too
will contribute to IMD. Performance should be verified using a spectrum analyzer.

- What PEP power output level were you able to obtain?

- How did you reverse the I.F. strip to provide SSB filtering on transmit? Or
did you add a separate TX SSB crystal filter? If so, how are you accomodating
USB and LSB operation, setting the BFO offset, etc.? What skirt selectivity were
you able to obtain? (Generally a 7 or 8-pole filter is required for acceptible
rejection of the opposite sideband.)

- How did you handle the VFO range issue? We recommend an 80-kHz range, with an
option for 150 kHz. But niether is adequate to cover both the CW and SSB
segments of most bands. (The exception would be 40 meters, outside the U.S.,
where the phone segment starts much lower in the band.) In order to get coverage
of the full band, you would presumably have to either accept much worse tuning
resolution from the 10-turn pot (about 30-40 Hz), or add a switch on the left
side of the case to select between two VFO ranges.

- How did you handle the band-pass filter bandwidth issue? The K1 uses a premix
design (as opposed to the K2, which generates an LO signal directly at the
needed injection frequency). This extra mixer stage complicates elimination of
close-in spurs. Because of this, it's of critical importance that both the
premix and RF band-pass filters be as narrow-banded as possible, and this is
facilitated by the small tuning range requirment (CW bands only). If you widen
the band-pass filters to accomodate full-band tuning by the VFO, chances are
that the harmonic content will be excessive on some or all bands.

Looking forward to seeing how you approached these design challenges. 

73,
Wayne
N6KR