Re: Very Late Start - Type 2

Clifford Heath
 

I bought this:

<https://www.aliexpress.com/item/Four-way-orthogonal-signal-generator-DDS-AD9959-core-board-200MHZ-AD9854/32713419146.html>,

but I recommend you spend $20 more and get one with transformers
or at least with video op-amps. The DACs in the AD9959 steer a
constant current through differential outputs, and it's important that
these outputs see the exact same load impedances to keep the
currents in balance. If not, the steered current fluctuates and that
makes the channels interfere with each other somewhat.

The bare chip is available (end of reel surplus) for ten bucks on
Aliexpress, if you can deal with the SMD.
<https://www.aliexpress.com/item/AD9959BCPZ-VFQFN-56-AD9959BCP/32787625498.html>

Second-hand gear is very expensive here in Australia. It's a small
enough market that it all gets bought by dealers who are prepared
to price it high and wait a long time.

Clifford Heath.

On 27 Sep 2018, at 8:46 am, wb6ogd <garywinblad@...> wrote:

Uh Clifford,
The eval board for AD9959 is $430 at Digikey.. Can you get those on ebay for cheap?

Si5351 board is about $7.

You might as well go buy a used HP or something, no?
I think I have about $25 in my PHSNA total out the door...

73,
Gary
WB6OGD


On 9/26/2018 3:32 PM, Clifford Heath wrote:
On 27 Sep 2018, at 12:09 am, wb6ogd <garywinblad@...> wrote:
True, the SI5351 is not best...
BUT, at higher freqs it's output becomes more sine wave. And at times, I thought I might want a higher freq
generator.
If you want higher frequencies, you should consider adapting PHSNA
to use the AD9959. You get four channels with a 500MHz core, so can
generate up to 200MHz sine waves. I've published driver code for it:
<https://github.com/cjheath/AD9959>

I'm using this in a new full multi-port VNA design which requires two
coherent channels (digitally phase locked, but sweeping on different
frequencies). I'll let you know how that progresses.

Clifford Heath.



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