HF DTMF & Necode Decoding

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Apr 5, 2003
These two selcal modes still are used quite a bit in latin ameria and necode still seems to be alive in the Gulf.

Of interest is the dtfm formats that were used by bramco as a steady two tone signal generated by two reeds and the later, budget variants by Transworld, Stoner, and Kachina that used the same principle, but used a simple ASCII character generator to send a very low baudrate ascii character using a two tone premable followed by an dtmf FSK ascii string with a verification tone sent by the decoder. Many of the inexpensive marine variants or non-type accepted SSB channelized units operating between 2-7 sold to developing countries used them. I don't know what the emission designator was or if there was a standard. I do know that Kachina's would not interoperate with with Transworlds. Same idea, but frequency difference was different IIRC. Bramco's used just a single two tone continuous tone. The decoders operated on detecting the difference between the tones, so both units could be pretty far off center frequency, but the decoder would reliable decode the call. These were used heavily by independent shore stations on both Northern and Communications Associates transceivers in a general all call configuration although single master and encode only slave units were made in both types of units.

Necode was another story. It relied on a broad range pll decoder and repetitve octal string containg a from and to code that was displayed on the unit. Loral and Motorola had a variant of it in early units.

Some years ago after the ATT breakup, there was a company in the gulf that attempted to use the necode and loral formats ported into the short lived SGC-7200 dsp sel cal unit and offered PC software with an encode only string registered to their network.

I know of no other then the Seacode DSC units manufactured by the original developer of necode for GMDSS applications and an authorized necode card manufactured for Harris's RF-230M power supply accessory bay and SEA's units as an option.

Was there or is there any software that can decode these formats. I do have one of the Kachina units that would be relatively easy to copy and the 128 possible stings can easily be sampled and placed into voice storage modules. This was a low tech, but very simple and effective system for low frequency tolerance transcievers.

I'd love to find a soundcard software package that can do the necode stings.

Was/has any of these formats every been available in an encode/decode pc software?
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