[Lowfer] KD5UWL dds exciter

[Zack Widup]

The AD9835 is probably adequate for this purpose. Less pins to solder!

73, Zack W9SZ

On Sun, Apr 19, 2009 at 11:22 AM, Eric Smith <esmithmail at gmail.com> wrote:

> Hi all,
>
> Finally _finally_ making some progress on my new dds exciter:
> http://www.nutstreet.net/radio/projects/dds/  I'll update this page as
> I go along.
>
> Some of you may remember that I've been using the ZL1BPU exciter for
> the last few years, and it has served well, but as designed it's only
> good up to about 400 kHz.  That has always been fine, but since
> modifying my Part-5 license to include 600m I've been wanting one that
> would operate into that range.  THIS HAS BEEN ONE OF THE SINGLE
> GREATEST HOLDUPS to me getting on 600m.
>
> SO I'm using the Analog Devices AD9851 DDS IC.  When I first received
> this item I had trouble trying to solder the tiny little pins (SSOP
> package).  I finally mailed one to Accutek Microcircuits who soldered
> it to a 28-pin DIP adapter (their part # AK28D300-TSOP).  This was $7
> including the adapter and the soldering.
>
> I'll post a schematic and a link to my (ever changing) source code
> soon.  I'm using GCC and the avr-libc library.
>
> Years ago Alberto (writes Argo -- thanks, Alberto, as always!) turned
> me on to Atmel's "ATmega" family of 8-bit RISC microcontrollers.
> These are a blast -- for this project I'm using an ATmega644.  Has
> more memory and some other features than I need, but I wanted the pin
> count.  The prototype you see in the picture is functional in that it
> will produce whatever frequency waveform I want from DC up to a little
> over 5 MHz (without engaging the DDS core's 6x clock multiplier) at
> approx .003 Hz resolution [ (1 * 12.8) / 2^32 where 12.8 is my system
> clock speed in MHz, see AD9851 datasheet], but I'm planning to add
> bells and whistles ... including an LCD and pushbuttons to allow front
> panel frequency and mode changes without having a PC hooked up to it.
>
> So I used the MCU to clock the phase, control, and frequency words
> into the dds core and strobe the frequency update pin after all five
> words are clocked in.  Then the output comes spilling out of the DDS
> IC, just that easy.
>
> The clock source is one of the two 12.8 MHz TCXO units Stuart was
> offering years ago, "free to good homes".  These have proven to be
> ultra stable.  I use the clock output of the MCU to drive the DDS core
> with the same clock.  I also divide the 12.8 MHz by 12800 in the MCU
> using a prescaler combined with 8-bit timer hardware on the MCU to
> produce a 1 ms clock which is the basis for a sleep-based delay
> routine I use in the project for setup and hold timing.
>
> Questions for you guys -- the digital hardware and software of this
> thing is dead simple to me, it's the analog side of things that I
> always struggle with.  So my questions for you are:
>
>  - given this 1V P-P waveform I'm producing, what is the best way to
> drive an amp?  That is, do I need to square this up?  Or will
> something like Lyle's complementary pair final do that anyway?
>  - any (simple) 600m final suggestions out there?  (the amp will
> quickly become my next biggest holdup)
>
> Thanks, guys,
> Eric  KD5UWL / WD2XFX
> ______________________________________________________________
> Lowfer mailing list
> Home: http://mailman.qth.net/mailman/listinfo/lowfer
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Lowfer at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>