[aprssig] APRS on all Radios!!!!

Scott Miller scott at opentrac.org
Sun Aug 17 13:55:07 EDT 2008

Makes sense... I know there's a lot of energy in the human voice 
spectrum below 250 Hz, but I suppose it doesn't have much impact on the 
intelligibility.  Is it safe to assume that the transmitter is high-pass 
filtering the mic audio to avoid interfering with the CTCSS tone?  And 
that the CTCSS frequencies are high enough to avoid getting eaten by the 


Mark Miller wrote:
> FM receivers that use CTCSS typically have a low pass filter (~250 
> Hz) that directs the CTCSS to the CTCSS deocder, and a high pass 
> filter that blocks the CTCSS from the normal audio chain.  FM squelch 
> circuits use another high pass filter (4K or so) that is used to 
> determine the quieting on a channel.
> 73,
> Mark N5RFX
> At 11:47 AM 8/17/2008, Scott Miller wrote:
>>I'm afraid I don't even know how the radio
>>suppresses the PL tone - 100 hz is most certainly within the audible
>>range.  Is everything filtered below a certain cutoff frequency, and if
>>so, what's the cutoff?
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