[digitalradio] I/Q Audio
An appeal to datamode software authors... Could anyone writing / contemplating any datamode software please consider incorporating I/Q stereo outputs and inputs. With SDR receivers becoming more widespread, I/Q audio inputs will allow direct use with simple receivers such as Rocky and homebrew ones without having to loop into an SDR prog, back out and into the datamode software. Generating I/Q audio on transmit is probably even more valuable. Receivers like the SDR IQ send a serial output which is just asking to be intercepted and used to control a DDS/Synthesizer LO for an upconverter, turning these receivers into point and click transceivers. The whole amateur SDR area has quite naturally, so far, concentrated on receive but its about time more attention was put into transceive operation. Having I/Q audio drive ready and available is the simpler home-brewable solution. At the moment at LF I've had to resort to making up all pass networks and accepting the narrow band of useful operation and need for careful trimming for good sideband rejection. See http://www.g4jnt.com/IQConverters.htm http://www.g4jnt.com/LFUpconv.pdf Have just been through all the installed datamode packages on this machine and the following MMTTY, Digipan, IZ8BLY Hell, ROS 1.6.2, WSJT7, WSJT8 even G3PLX's PSK31SBW and teh brand new CMSK all failed the test, giving an annoying pair of identical sinewaves from left and right channels on the scope. Only MultipPSK gave a nice pair of quadrature sinewaves on the audio drive, so this comprehensive bit of software is my clear winner so far. Datamodes intended for LF/VLF could be considered one of the more important targets as commercial transceivers are hardly ever used here, and direct I/Q upconverters are almost trivial at these frequencies. Andy G4JNT
[digitalradio] Direct RTTY Generation
A back-to-basics question for once... Is there any modern RTTY datacomms software that gives a single wire digital output for driving an FSK transmitter? Looked in the MultiPSK and MMTTY setup menus and nothing. While I realise there may be little call for such a one-wire drive now (although my not-too-old IC746 will take a RTTY input signal) it does lend itself to simple QRP designs for the less experienced constructor. Andy www.g4jnt.com
[digitalradio] NUE PSK31 Modem
Does anyone have a valid web address for the NUE PSK31 Modem now. All the ones found on a Google search seem to be broken Andy www.g4jnt.com
[digitalradio] (unknown)
The term "Spread Spectrum" can apply to any mode that spreads its energy over more than the necessary bandwidth. If we assume the necessary bandwidth to be equal to the signalling rate than anything other than single carrier modes technically fall into this category. Even WSPR coul dbe considered spread spectrum! Its 6Hz bandwidth is wider than the 1.5 B/s rate. Within the WSJT suite, JT65 is more of a spread spectrum mode, and outside Joe's suite, MT63 with its 2.5kHz for a few tens of Bits / second is even more extreme. Andy www.g4jnt.com
[digitalradio] (unknown)
Strictly, CW is a three symbol code with source coding (variable length alphabet, like varicode) with soft decision coding, and mild FEC (operators interpretation of the code based on S/N) and some convolutional coding with soft decisions (matching characters received against patterns / words. Once you start using soft decision decoding, error correction and mult- bit-per-symbol waveforms, it becomes a bit difficult to really call anything a digital modulation at all. Especially when analogue processing is mostly performed digitally now, anyway Andy www.g4jnt.com
