[Elecraft] Re: K1 SSB?

[giuliano]

Answers on the text
Thanks for your interest

73
Giuliano I0CG




----- Original Message -----
From: "Wayne Burdick" <n6kr@elecraft.com>
To: "giuliano" <giulianori@libero.it>
Cc: <elecraft@mailman.qth.net>
Sent: Wednesday, April 23, 2003 8:33 PM
Subject: K1 SSB?


>
> 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.

I have made  a polarization network; i have about 150 ma IC current without
modulation, i think that now the PA is running Class-AB

 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.

Seems that predriver Q6 is  class-A via the R28-R29 polarization circuitry.
I am making same measures with my Spectrum analyzer

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

About 6-7 W on SSB and 4-5 W on CW
>
> - How did you reverse the I.F. strip to provide SSB filtering on transmit?
Or
> did you add a separate TX SSB crystal filter?

Yes i use two separate crystal filters . Reception filter with 6 crystal and
TX with 4 crystal


>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.)

In the next day I insert on my WEB page plot of RX and TX filters.
I change the BFO frequencies auomatically when i switch on the front panel
FILTER1/2/3.
For this i use two Cap. trimmer and one diode.

> - 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.

Now i have add a 68 NPO cap. on parallel to the 120 Cap. supplied.
So the tuning range is about 250 KHz. It seems that stability and tuning are
adeguate.Specially on Europe where on 40 m we use only 7000-7100 band .
I am working, to solve better this problem, with a DDS AD9834 and a tuning
encoder with 10/100/1000 Hz selectable tuning step.
It is the next modification step.



> - 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.

I have measured the Filter selectivity, (see also my filter plot on my Web
page) and seems that selectivity is adeguate to cover 350 KHz on 20 M and
150 KHz on 40 m.

>
> Looking forward to seeing how you approached these design challenges.
>
> 73,
> Wayne
> N6KR