[Elecraft] Re: K1 SSB?

[Wayne Burdick]

Hi Guiliano,

Thanks for the further clarification.

giuliano wrote:

> 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

OK. You'll want to check the PA device temperature during long key-down periods,
but the side panel should provide adequate heat sinking at this bias level.


> > - 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

Did you measure the opposite sideband rejection and carrier suppression? We
needed 7 crystals in the K2 to obtain really good results.


> > - How did you handle the VFO range issue? 
>
> Now i have add a 68 NPO cap. on parallel to the 120 Cap. supplied.
> So the tuning range is about 250 KHz....
>
> 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.

This will work, but are you also planning to include a phase-locked loop to
clean up the DDS's output? Using DDS as the injection oscillator by itself will
significantly degrade the performance of the K1's receiver. The spurious-free
dynamic range of any DDS with a 10-bit DAC, including the AD9834, will only be
in the 60 to 70 dB range at best. Large in-band signals will mix with the spurs
to produce numerous "ghost" images within the passband. This would be especially
noticeable during contests, but could be a problem anytime the band is open or
if you have strong nearby stations. For this reason, raw DDS VFOs are only
acceptible the simplest of equipment, or if the operator is willing to accept
the compromise.

I wouldn't bring this up except that the K1's present performance is
outstanding, and anyone contemplating making a DDS mod should be aware of the limitations.


> > - How did you handle the band-pass filter bandwidth issue? ...it's of critical 
> > importance that both the premix and RF band-pass filters be as narrow-banded as possible
>
> 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.

This would provide useful range on 20 m and up, but on 40 m the range would be
adequate only for non-U.S. K1 owners. In this case, as well as on 80 m, you'd
need to tune the filters for either CW or SSB.

By the way, did you make these measurements using only the 2-band filter board?
The 4-band board's bandwidths are quite a bit narrower because of the high-Q
inductors and the multi-band switching arrangment. It just covers 80 kHz on 40
meters, for example, and I believe the usable bandwidth on 20 meters is 200 kHz
or less.

Thanks,

Wayne
N6KR