And even more.....

Well,

Following on from the basic DDS VFO I got going yesterday here:

http://g0mgx.blogspot.co.uk/2014/01/yet-more-ddsing.html

I've done a little bit more.

I started with the software package QUCS I mentioned back here:

http://g0mgx.blogspot.co.uk/2013/12/qucs-simulation-you-what.html

And entered the parameters for a 25MHz cut off low pass filter, the tool designed the filter for me and I edited it to enter real world component values:

I then simulated the filter and got this result:

So I made it, now, to get the inductors correct, I just use the mini ring core calculator and pick a known inductor, enter the inductance I want and it calculates the number of turns for me. As long as that isn't too few to be practical or too many to fit, I go with it:

And this is what it looks like built and attached to the output of my DDS:

The output now looks like this terminated in 50R at the 'scope:

and this is the view on the Spectrum Analyser:

So, all in all, looking much better than before. I even found the trimmer tool and tweaked the band pass filter I made from the designs on the G-QRP pages, it looks like this at the moment:

and here's the sweep of the filter:

Cat's not been helping much:

Good, though, egh?