[aprssig] APRS on all Radios!!!!

Wes Johnston, AI4PX wes at ai4px.com
Sun Aug 17 14:34:43 EDT 2008

Since many repeaters use PL tones, I can see how a low tone might get in the
way of any given PL tone.... 67hz is the lowest PL tone, so this "data"
could be sent at <67hz.  Since we have two power standards on 50 and 60hz,
best to avoid those frequencies too.  maybe split the difference at 55hz?
or somewhere between 60 and 67 hz?  62.5 might be a nice frequency.  Of
course we have to select a frequency that has no harmonic on any standard PL
tone frequency.

I have yet to understand how the average "joe ham" will inject low frequency
audio?  Perhaps using the 9k6 pin on the mini-din?

I like Scott's assertion that we use straight BPSK data, not vaircode.  But
we'd need to modify a hardware PSK 31 decoder (like the Nuepsk device) or a
PC program to decode psk31 as BPSK not varicode.

Our lives begin to end the day we become silent about things that matter

On Sun, Aug 17, 2008 at 1:55 PM, Scott Miller <scott at opentrac.org> wrote:

> 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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