Re: LF: 'Ugly weekender' build: passive CW audio filter, used on MF

[Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>]

Hello Wolf,

Thanks, very interesting. Aaah, actually i should finish other projects 
before starting a new one, but this time it may actually become a short 
new project ;-)
I will try something similar as well :-) An analog filter (without a PC) 
will allow full-BK CW operation :-)
73, Stefan/DK7FC

Am 19.01.2014 13:47, schrieb wolf_dl4yhf:
> Greetings all,
>
> I took the opportunity yesterday evening (with lots of stations 
> crowded within a few hundred Hertz on MF) to test this ridiculously 
> simple "passive narrow-band audio filter" on air (between RX and 
> headphone) :
> http://www.qsl.net/dl4yhf/passive_lc_audio_filter/passive_lc_cw_audio_filter.htm 
>
> (just two LC resonators, one of them adjustable with a 'hex' rotary 
> switch ie 16 different selectable center frequencies).
> The results were quite stunning, compared with a long FIR filter 
> (implemented in software), this ugly design helped a lot in the QRM / 
> QRN .. less 'ringing' than expected from such a simple circuit.
>
> 73,
>   Wolf DL4YHF .