On Mon, 01 Dec 2008 14:13:23 +0000, Dave wrote:

JosephKK wrote:
On Sun, 30 Nov 2008 22:52:16 +0000, Dave wrote:

JosephKK wrote:

Which make and model / series? There are dozens of variations.

These are the standard CTCSS freqs:

http://www.batnet.com/~mfwright/ht220plcodes.html

http://en.wikipedia.org/wiki/CTCSS

Have you read your own references?

Bottom line, most any tunable tone decoder.

If a vibrating reed can be considered a "decoder" then you are correct.

However, there are not "dozens of variations".

Sure can. Collins Radio used mechanical resonators in an HF radio ISB
diversity 2240 baud modems. Then they used a switched capacitor meta
resonator. Then they used DDS synchronous comparison. And of course
there are various narrow band filter methods. And of course whatever
internal method the 8870 DTMF decoder uses. Who knows what methods
can be implemented in fast UC or small DSP or even an FPGA, except it
will not be a mechanical resonator. I suppose a mathematical model of
a mechanical resonator though.