[Lowfer] New LEK exciter

[Lyle Koehler]

>Interesting. Hmm, why the changes (and so soon)?

Basically I just like to build stuff, and I can't resist making changes,
even to a perfectly good design. But in this case, I also wanted another
copy of the DDS exciter so that I can play with one of them on the workbench
while the other one is tucked away and beaconing its little heart out.

>Was it just to
>eliminate the IC PA and other "overhead" or is it an improved design
>that also uses less components and those more readily found?

Yes and no. It isn't necessarily an "improved" design, depending on how you
plan to use it. However it does use less components and I believe it is now
possible to get all of the parts from a single vendor (famous last words)!
Aside from the AVR microprocessor, which is available from a number of
sources in the US, the circuit uses generic components such as a 74HC14 hex
inverter, a 5-volt regulator, three general purpose transistors (two PNP and
one NPN) and miscellaneous diodes, resistors and capacitors. I used a lot of
stuff that I had on hand, and have not generated a detailed parts list. With
a cheap 12 MHz microprocessor crystal, a set of parts might cost around 10
bucks (excluding shipping and handling). For serious weak-signal stuff,
though, the $15 12.8 MHz TCXO is probably worth it. One of the guys on the
reflector offered to bring some TCXOs back from Japan at a real bargain
price -- might be worth reserving a few to add to my stock. Unfortunately I
may have deleted that message along with all the junk postings :-(

By the way, it looked like my frequency stayed within +/- 0.1 Hz overnight.
Maybe I was lucky and got a 12 MHz crystal with a low drift, and maybe it
was just that the temperature in the shack stayed fairly constant. Also, I
think I've fixed the glitch in the "symbol clock" oscillator (two sections
of the 74C14) that caused the erratic CW keying. Now for the hard part --
converting the scribbled schematic into something readable to put on my web
site.

Lyle, K0LR