Leif, I had never given too much thought to that idea before, but two I/Q ISB signals should be used to be translated to the working frequency, using the same two carriers in quadrature on the PC. That allows to use existent hardware, and I believe it is advisable to use I-Q signals to be able to take adventage of image rejection mixers as many designs I have seen (Softrock, YU1LM, etc) do to keep spurious outputs low.
You will hardly see ISB on "hardware radios", except on very special and costly ones, because it doubles quite a bit of the low level and filtering circuits, and thus, increases cost considerably. It also means that linearity must be improved, because adjacent channel IMD now falls on another desired signal, I once worked on a half kilowatt ISB transmitter using a 5-500 tube on the final. No wonder, as that tube has an IMD of -52 dB as AB1 amplifier. If SSB is generated by the phase shift method on a PC there is no rigid bandwidth limit as with IF filters (xtal, mechanic) . On most SDR's the main selectivity measures seem to be taken on the PC, and only the latest softrocks have RF bandpass filters, which I believe to be a good choice. Dreaming a bit, I believe that ISB could be something to consider for the Linrad transmitter. As I see it, usually the ISB modulator should be disabled and the transceiver should work as a common SSB tranceiver. If someone who knows what he/she is doing desires to use ISB, then that could be enabled. Actually, the whole transceiver should be capable of being toggled from SSB to ISB and viceversa, perhaps by some configuration command. Also, how much extra code is required must be weighed, as it is to be expected to increase the CPU loading as well, so it may not be something for the feebler CPU's. There are quite a few details to be worked out, without losing sight of common sense. About inputs, on Windows, some sort of "virtual audio cable" might prove convenient, say, for SSB/SSTV. On Linux perhaps some juggling with Jack might allow it. 73, Jose, CO2JA Leif Asbrink escribió: > Hello Jose, > > >> I have seen no software capable of generating it so far. Actually, it >> would require two sideband generators. I am not sure if a single sound >> card could actuallydo it. >> > It is a trivial thing to generate ISB in the PC and send it to the > soundcard. Nobody is interested because there is not any hardware > available to frequency shift it to RF and to amplify to a suitable > power level. > > One could make a signal with about 5 kHz bandwidth available on a single > audio channel. It would match an SSB transmitter with a passband from > e.g. 300 to 5300 Hz. One could also make it available as an I/Q pair with > i.e. 300 to 2500 Hz passband (stereo). That would fit a simple quadrature > modulator. > > >> ISB has not been usual among hams, but could be interesting. Once I read >> a proposal for using SSTV on one sideband and audio on the other, >> but have heard noone doing that. >> > The problem is the amplifier chain. Conventional equipment does not > have the bandwidth in SSB mode. > > I think we will see experimenting with ISB and other new modulation schemes > when we have more digital equipment around. The HPSDR, Mercury+Penelope > would allow voice+SSTV as ISB or in some suitable digital format > and everything would be in software. > > I could easily transmit ISB with my Linrad transmitter, but I do not > have any second signal besides the microphone (No SSTV.) It will not > be interesting until there is a reasonable chance of meeting someone > on the bands who is capable of receiving both sidebands. I am sure we will > see it some day because it is an obvious thing to implement in a SDR > transceiver:-) > > 73 > > Leif / SM5BSZ > > Participe en Universidad 2010, del 8 al 12 de febrero de 2010 La Habana, Cuba http://www.universidad2010.cu --------------------------------------------------------------------- SEGUNDO SEMINARIO INTERNACIONAL LEGADO Y DIVERSIDAD. ARQUITECTURA Y URBANISMO. El rescate de los valores urbanos y arquitectónicos en tiempos de globalización Colegio de San Gerónimo, La Habana Vieja, noviembre 24-27, 2009 ---------------------------------------------------------------------
