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 CW notch filter 
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Post CW notch filter
Hi there purveyors of wisdom!

My old 747 has got sicker and sicker and has sadly been boxed up and put away to be canabalised at some point, and I've got a new (to me) FT 840

the CW notch filter is not fitted and naturally Yaesu dont make them any more and they cost a fortune on eBay

going old school, I've seen external audio filters that go in the audio output ..... Timewaves and the like. and other much simpler home brew solutions.

are these really going to do a similar job?

thanks!

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Sun Jan 31, 2021 1:12 pm
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 CW notch filter 
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Post Re: CW notch filter
MI0OIM wrote:
Hi there purveyors of wisdom!

My old 747 has got sicker and sicker and has sadly been boxed up and put away to be canabalised at some point, and I've got a new (to me) FT 840

the CW notch filter is not fitted and naturally Yaesu dont make them any more and they cost a fortune on eBay

going old school, I've seen external audio filters that go in the audio output ..... Timewaves and the like. and other much simpler home brew solutions.

are these really going to do a similar job?

thanks!

Notch filters were always inserted within the audio line stages of a transceiver, if in built usually in the lower level pre volume control audio stages.
External ones just do it at the audio output point, but work on exactly the same sweepable narrow bandwidth audio notch principal.
As you say there are many homebrew versions kicking around, I have built a few over the years for either radio use, or as a feedback notch filter for electro acoustic guitars.
The only difference being the frequency range, Q, and where in the audio spectrum they are centred upon.
Most simple notch filters are narrow bandwidth "inverted" sweepable "peak" filters, an example of a sweepable narrow bandwith "peak" filter being the Wah pedal of electric guitar fame.

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Sun Jan 31, 2021 2:02 pm
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 CW notch filter 
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Post Re: CW notch filter
Keep your eyes open for a Datong FL1, FL2 or FL3

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Sun Jan 31, 2021 4:20 pm
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 CW notch filter 
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Post Re: CW notch filter
great stuff, thanks.

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Sun Jan 31, 2021 5:50 pm
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 CW notch filter 
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Post Re: CW notch filter
have a look here, check out the SCAF filter, it may sute your needs,
https://www.phoenixkitsonline.co.uk/
73 John M0CDL Fists.


Mon Feb 08, 2021 4:23 pm
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 CW notch filter 
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Post Re: CW notch filter
Datong FL3, has 2 notch filters (auto and manual), spot on for cw and ssb use
Look at youtube videos

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Thu Apr 08, 2021 10:14 pm
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Post Re: CW notch filter
I rarely use a notch filter, however this is how I found an ordinary band pass (peak) filter I made a week or so back.

viewtopic.php?f=7&t=117770

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Fri Apr 09, 2021 5:28 am
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 CW notch filter 
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You have to be carefull the auto notch does not wipe the CW tone you are receiving, heres a cw demo
https://www.youtube.com/watch?v=c_BWamW ... ikesMovies

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Fri Apr 09, 2021 6:26 pm
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 CW notch filter 
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Post Re: CW notch filter
G4XNG wrote:
Keep your eyes open for a Datong FL1, FL2 or FL3


I have had the FL1 and the FL2 both fantastic for CW trouble is they don't come up for sale that often
good luck trying to find one .

Regards Frank G4YLJ

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Sun Apr 11, 2021 1:40 pm
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Post Re: CW notch filter
Sangoma wrote:
I rarely use a notch filter, however this is how I found an ordinary band pass (peak) filter I made a week or so back.

viewtopic.php?f=7&t=117770


I just built another (PC board corrections) and measured the bandwidth.

-3dB points are 19Hz either side of 700Hz and 10dB points are 65dB either side of 700Hz

Easy to build on proto board, plenty of circuits on the net, this is one http://www.alg.myzen.co.uk/radio/qrp/af_filter.htm but compare the others for values.

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Mon Apr 12, 2021 3:38 pm
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