[CW] NEScaf switched capacitive audio filter

[pa0wv]

Petr Ourednik schreef op 2018-06-18 07:28:
> Hi all,

As generally known your brain filters, so cw in wideband noise (300-2800 
Hz) and CW band limited to 250 Hz are decodable with the same error 
rate.

However when you narrow the filter to 50 Hz you can copy better because 
that filter is narrower then your brain filters.

Everything without QRM only white band limited noise noise in the 3 
cases the same strength. and the Morse code the same PEP in the 3 cases.

Which cases? Listen by dpwnloading the 3 sound files on my website 
https://pa0wv.home.xs4all.nl/cw_archive/

Small filters , mechanical or electrical, has often severe ringing. You 
have to test with Morse code, and switched capacitor filters build 
around an IC of Maxim are 8 pole chebyschev. certainly not phase linear.

The 3 example files are produced bij 1025 element FIR filters.

PA0WV
73=30
> 
> as Mike wrote I can confirm it is great feature for your rig. I tested
> few of them and
> after proper building it run for the first shot and works like champ.
> You will be amazed with the improvement of your radio using the NESCAF 
> box.
> 
> 73 - Petr, OK1RP
> 
> On Sat, Jun 16, 2018, at 1:54 AM, w9oj at indy.rr.com wrote:
>> The NEScaf is a switched capacitive audio filter. It is designed to be
>> simple to build and use.
>> 
>> It is more flexible than previous filters for QRP rigs. It has two
>> panel-mounted controls — a single center-detent potentiometer that 
>> sets
>> the center frequency of the filter’s bandpass (default value settable
>> between ~415Hz and ~1kHz), and a dual-ganged potentiometer that 
>> provides
>> a continuously variable bandwidth control (from ~60Hz to ~1500Hz). 
>> This
>> ability to smoothly vary the bandwidth is very useful.
>> 
>> The NEScaf is designed to be driven with a phones or speaker level
>> signal. No hacking into your rig — just connect it to the headphone or
>> speaker output of the radio. This makes it usable with several radios.
>> The board is small enough, at about 2 inches square, to build inside
>> many radios however, if you so choose.
>> 
>> 
>> http://www.newenglandqrp.org/wordpress/nescaf-a-switched-capacitor-audio-filter/
>> 
>> 
>> 
>> 73 de Mike W9OJ
>> 
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> 
> 
> --
> 73 - Petr, OK1RP
> --
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