DIY CTCSS filter for streaming

[SEQLD_SCAN]

Hi all,

I run a 24/7 stream on radioreference.com
http://www.radioreference.com/apps/audio/?feedId=4450
The CTCSS tone on this stream is 107.2Hz. I have found it is quite audible when listening to the stream via my computer speakers, which have a subwoofer attached.
The subwoofer really makes the 107.2Hz stand out.
I looked for a software-driven equalizer but they are all too expensive or just don't work.

Overnight, I had a brainwave and thought about trying a passive high pass filter.
I put this simple twin-t circuit together in a spare DB25 backshell.
The socket and plug are held in place with hot-melt glue.
The component values have been calculated to give a deep notch at 108Hz.
This works brilliantly! Cost less than $4 in parts and only an hour of my time.
It connects between the scanners speaker-out socket and the PC's line-in.

The calculations and circuit diagram can be found here:
(Sample)Twin-T Notch Filter Design Tool - Result -


Cheers,
SEQLD_ SCAN

 

[talkpair]

Good job.

I don't even hear a hint of the tone.

 

[PeterGV]

Clever. I've wanted to do this for years. You can hear the PL tones through my scanner very clearly in local audio, especially (as you said) with a sub-woofer connected.

But... the circuit is for notch filter and not a high-pass filter, isn't it? Did you simply notch-out your specific PL tone? A high-pass filter that eliminated ALL PL tones would probably be most helpful.

Peter
K1PGV

 

[SEQLD_SCAN]

Yes, this is a notch filter.
I wanted to preserve as much audio as possible. A high pass filter would be OK, but it might have rolled off too much of the low end.