[aprssig] APRN news from Dayton!

Bob Bruninga bruninga at usna.edu
Wed May 25 10:35:23 EDT 2011

Traffic Cams:

One use of these SSTV cameras might be on telephone poles along one's
commute at the critical traffic points.  A driver can key up a PL tone and
the next camera in range will send its view on some UHF channel to be
displayed on a laptop running any SSTV soundcard software.

The entire control system and RF hardware would cost only about $15 if it
were not for the prohibition against tones (longer than 10 seconds) on the
FRS channels.  I love the little COBRA CXT90's that have both CTCSS and DCS
and can not only scan the channels but also the CTCSS and DCS to find who is
on what tones.  They also have VOX and cost less than $15 each in pairs.

The one problem is that I have not found a reliable DC point somewhere
inside the radio that changes TTL level when it decodes a tone.  Actually,
it is easy to find many such points, but as soon as the radio goes into
power-saver mode and starts pulsing the receiver, every point in the radio
starts pulsing too.  So the easiest thing to do would be to simply use an
external VOX circuit on the speaker output to key the SSTV camera, and then
it's noise would key the radio's VOX for the transmission.

A press of the obnoxious CALL button in the mobile would start the process.

Too bad the FCC prohibits tones (the SSTV) longer than 10 seconds on FRS...


More information about the aprssig mailing list