Digital ATS3 - MFSK modes implemented Hi gang.
I implemented MFSK remote modulation into ATS-3a firmware. I also extended PocketDigi to make use of it. The little transceiver in Altoids tin is now able to send a lot of digital modes if commanded by PocketDigi, namely: CW, BPSK31, BPSK63, QPSK31, RTTY, MFSK16, Olivia, Contestia, RTTYM Additionally it is possible to set frequency from PocketDigi. Only CW, RTTY and MFSK16 are transmitted according to their definition. BPSK31 and BPSK63 signals are shaped by CW envelope, not by raised cosine, which makes them wider than necessary. Nobody complained yet if I transmit at QRP levels. QPSK31 signal shaped by CW envelope is very difficult to decode. Pawel Jalocha designed a special envelope for Olivia and modes derived from it - Contestia and RTTYM, which shall minimize intersymbol interference. ATS-3 is only able to do hard MFSK without shaping. According to my experiments it degrades reception only slightly. Although DominoEX or ALE modes are not implemented in PocketDigi yet, they both may be modulated on ATS-3 without additional firmware changes. I tried to cheat Throb/ThrobX decoder by sending the tone pairs not parallel, but one after other. It really did not work. MultiPSK only decoded 1 Throb per second signal, when it was strong enough. But it was fun anyway. I tested, how the MFSK decoders in PocketDigi would cope with the narrow ladder filter in ATS-3. The filter is wide enough for PSK or RTTY. 250Hz wide MFSK modes (MFSK16, Olivia 4/250 and 8/250) work, but tuning is a bit difficult. The wider Olivia modes are not readable on ATS3, although the transceiver is able to transmit them. One may do cross mode QSOs, transmit wide MFSK to let the other side exploit higher coding gain, but to receive narrow band mode. One could make the ATS-3a IF filter wider by choosing lower capacities and matching its lower impedance. I would like to try tuning the filter by MW varicaps like in the Elecraft RIGs. The finals of ATS-3 may be easily blown by MFSK modes. The transeiver shall be powered from low voltage to keep output power low or some heat sink has to be added, or preferably both. Elecraft KX1 with its variable IF filter and solid final seems to be a good target for digitalization. It is a pitty that Elecraft keeps its firmware closed source. My next step is to simplify the external interface. I plan to substitute the Bell 202 demodulator by a simple op amp slicer and to change modulation from AFSK to Manchester. I hope to squeeze the interface into the main ATS-3 Altoids tin. I am looking forward to do some RTTY QSOs with the upgraded RIG. 73, Vojtech OK1IAK
