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[aprssig] Modem tones, the KPC3+, and Bell 202

Bob Bruninga bruninga at usna.edu
Wed Aug 11 14:46:24 UTC 2010


> KPC3+ ... was 1300 and 2100 Hz.
> is a V.23 modem, not a Bell 202 modem.
> "Why... would anyone build in a 100 Hz'error'

My recollection is that when they redesigned the KPC-3+ hardware there were no 202 chip modems availalbe anywhere.  The only chip on the market was V.23.

The short life-cycle produciton life of modern electronics chips is freightening for long lasting system.  Its like teh D7 HT... At 12 years old, some of the chips were just not obtainable anymore...

Same errors exist in HF packet.  When I found hundreds of surplus bell 103 cards at Dayton one year back in 1978 or so and packet was just authroized for HF, the first hundreds of packet users on the air used these modems... 200 Hz... AMRAD and TAPR then adopted that standard...  But RTTY used 170 Hz shift.  Over the years, many multimode TNC MFR's got sloppy and did not want to support them all, and simply use 170 Hz  for RTTY -and- packet and hope that packeteers won't notice...

Good luck!

Bob, WB4APR



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