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From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
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Date: Sun, 19 Jan 2014 16:19:54 +0100
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Subject: LF: RE: 'Ugly weekender' build: passive CW audio filter, used on MF
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Hi Wolf,

I have similar good results with my old Datong FL3 analog (active) NF filter on my IC-706.
I've seen these Datong filters offered on ham fests for as low as 30 Euro.
Unfortunately no filter helps against strong TX side band noise...

73
Clemens
DL4RAJ  

>-----Original Message-----
>From: owner-rsgb_lf_group@blacksheep.org 
>[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of wolf_dl4yhf
>Sent: Sunday, January 19, 2014 1:48 PM
>To: RSGB LF Group at blacksheep; RSGB LF Group at Yahoo
>Subject: LF: 'Ugly weekender' build: passive CW audio filter, 
>used on MF
>
>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 .
>