[Collins] DDS-2A?

[jbrannig at optonline.net]

When I first saw the AOR DDS, I was hot to get one for my S-line.  Among the other features was a RS-232 connection for computer control, then I found out that the US version did not support the RS-232 because of some FCC compliance problem.........nuts.....
I went for a "daughter board" and added a few crystals and while using the S-line add the frequency manually to my logging/contest programs...(sigh)

Jim

> On Thu, 2005-05-19 at 06:04 -0500, cory wrote:
> > The topic of DDS generators for VFO's came up on the QRP list.
> > >From there I looked up the AOR DDS-2A, which is a high-end
> > implementation. 
> > 
> > Has anyone built a lower-end solution, just to replace
> > the crystal bank?   
> > 
> > I see the crystal packs on eBay from time to time and am still
> > thinking about Glen's internal switch arrangement.  
> > 
> > de ah6gi/4  Collins 75S-1 serial number 55. 
> 
> In a dds, it takes the same complexity to clean up spurs whether a few
> frequencies are needed or continuous coverage is needed. That 
> especiallyapplies to the number of bits used in the adder and the 
> D/A. I tried
> that once going to the extreme of using the most significant bit 
> out of
> the counter as my synthesized signal. It had spurs all over the 
> desiredspectrum. Maybe if the frequencies needed are round 
> numbers, you can
> simplify the controls but not the synthesis. Thing is these days, you
> can buy a single chip to do all the synthesis and so save on real 
> estateon the PC board and probably on project cost.
> 
> In my 75S-3B, I mounted a little aluminum plate on the top end of the
> tuning rack with a SPDT miniature toggle switch and a crystal 
> socket. I
> wired them to the oscillator circuit with miniature coax (RG-174 or
> RG-196) removing fixed C to account for the capacitance of the coaxes.
> Its been working that way for decades. I can change crystals with only
> lifting the lid a couple inches. Somewhere in a box, I have a 30
> position rotary switch in a box with 30 ceramic crystal sockets 
> epoxiedtogether figuring hanging that outside the receiver case. 
> Its not been
> wired yet. The single socket has worked well enough.
> 
> -- 
> 73, Jerry, K0CQ, Technical Advisor to the CRA