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?

QUCS Simulation - You What?

Well,

Been fiddling today with a new piece of software I have found called QUCS - the Quite Universal Circuit Simulator. It's a really neat open source project you can find here:

http://qucs.sourceforge.net/

There is lots and lots to this package, but my interest is in simulation of filter designs. Here, for example, is the design of a 9th Order Low Pass Chebyshev filter for a 4.2MHz target cut-off:

The package will design the filter for you based on your selected parameters but then you can tinker with the values to replace the theoretical calculated values of the components with real ones and then simulate the filter behaviour before and after. Here's the simulation of the filter above:

Now, I need to build the filter and see how close the simulation is to real world, but this looks like a very interesting package that I think will come in very handy indeed!

Good, egh?