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[aprssig] APRS on all Radios!!!!

Scott Miller scott at opentrac.org
Sun Aug 17 17:55:07 UTC 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 
PLL?

Scott
N1VG

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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