[Elecraft] Re: K1 SSB?

[Wayne Burdick]

Hi Trevor,

Trevor Jacobs wrote:

> What about the new AD995X series with the 14 bit DAC? The inproved
> resolution of the DAC should lower the spurs well below the 60 dB range.

The SFDR of the AD995X series is about 95 dB, I believe, and it's certainly a
cleaner part than the 983X series. But it will still not be nearly as clean as
an analog (L-C) VFO. Its spurs would still be the limiting factor in receiver
in-band image performance. It's also quite expensive.

You'd also need:

- a low-jitter, VHF crystal reference oscillator for good phase noise performance

- at least 3 spare I/O lines on the MCU to drive the DDS, and more if you include
  a PLL (the K1's microcontroller at present has no spare I/O lines)

- a shaft encoder (preferably optical: $15-$20 minimum; contacting-type encoders are
  a lot less expensive but have about 1/100th the expected rotational life

- some means of reading the position of the RIT offset pot and controlling the
LEDs and LCD
  (this implies integration of the new modification with the K1's present microcontroller)

In summary, adding DDS control to the K1 (inculding the recommended PLL) would
require numerous hardware changes. This would make much more sense as a total
redesign, taking advantage of the fact that no premixer or TX mixer would be
required, and adding broader band-pass filters, a display with more digits, etc.
By the time you finished, it would be a much more complex and expensive
rig--perhaps a K2 would be a better choice  ;)

73,
Wayne
N6KR