andre.kesteloot at verizon.net
Thu Jan 3 16:17:27 CST 2013
Very promising results indeed.
On 1/3/2013 13:54 PM, Karl W4KRL wrote:
> I ordered an AD9850 DDS Arduino shield on eBay for less than $6. It
> should be here from Thailand at the end of the month.
> A quick reading of the application notes suggests that the output
> should go through a 70MHz low pass filter for use in the 0 to 40MHz
> range. There are several nice on-line filter designers:
> But after looking at the low-res circuit jpg on eBay it turns out that
> it has an on-board filter. The values are vaguely similar to what the
> on-line designers calculate for a 7-pole Butterworth Pi but each
> inductor is shunted with a small capacitor. I thought it would be
> interesting to figure out what the filter was supposed to do and
> looked unsuccessfully for an on-line circuit simulator. There is a
> fair one sponsored by Digi-Key at http://www.partsim.com/simulator but
> I found it so awkward to use that I gave up after drawing the circuit.
> It did not produce any useful results.
> Then I came across idealCircuit at http://ic.sidelinesoft.com/
> The download is only 1.4MB and is free. There are probably a lot of
> limitations but it looks good enough for quick general use. One
> obvious drawback is the lack of part IDs. Maybe there is a work around
> in the manual.
> I drew the filter and got a voltage and phase graph in just a few
> minutes with zero frustration. The circuit and results are attached.
> It seems to be a 70MHz low pass with some ripple and peaks near
> cutoff. _Comments on the design and performance of the filter are
> welcome. Why did they shunt the inductors with caps?_
> Happy New Year
> Karl W4KRL
> Tacos mailing list
> Tacos at amrad.org
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Tacos