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

To: RSGB LF Group at blacksheep <[email protected]>, RSGB LF Group at Yahoo <[email protected]>
Subject: LF: 'Ugly weekender' build: passive CW audio filter, used on MF
From: wolf_dl4yhf <[email protected]>
Date: Sun, 19 Jan 2014 13:47:46 +0100
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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 .


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