[Qucs-devel] Re: qucs-filter

[Vincent <10...@fr...>]

Stefan,

> I've just sent Raimund some patches which also incorporate changes to
> the QucsFilter program.  I've built in the qf_* files sent in by Vincent.

> The only thing missing is now a Qucs Schematic creation.
> 
> Also I've some questions to Vincent:
> 
>  1. It looks like there is a bug during the BANDPASS/BANDSTOP creation:
>     the if (j==ncomp) break; condition does not work...
>  2. What's the exact meaning of the stopband frequency for bandpass/
>     bandstop?

Verschiedene Dinge :)

1. I'm in the process of cleaning up the qf_poly file. It is also 
undergoing a major change, in that "qf_poly" class shall now be only a 
pointer to a struct polynom. That way, we spare the overhead of copying 
polynoms when performing arithmetical operations, while preserving the 
ease of notation. Some redundant variables have been wiped out.

2. I have begun, but not yet finished, the integration of "traditional" 
Butterwoth and Chebychev filters into the new frame.

3. I know there is a bug in bandstop design, that I had no time to 
really chase out. For the bandpass, the parameters are :

	1. The center frequency;
	2. The bandwith;
	3 and 4. A point in the stopband where the attenuation is known.

E.g : let's synthesize a bandpass filter whose center frequency is 10,7 
MHz, bandwith 25 kHz and that rejects by more than 70 dB an image 
frequency at 30 MHz.

The bandstop specification is actually the same, but, for a reason that 
I do not know, I can't really make it work that way (the bandwith is 
always less than specified, though all other parameters work fine).

I'll correct the erroneous condition.

Cheers!
Vincent