hola amigos, manolo, muy interesantes tus pruebas de hell en 80m. casualmente he encontrado esto: http://www.qsl.net/zl1bpu/IONO/LittleTX.htm y me ha hecho pensar que se podrian hacer ensayos/estudios de propagación NVIS en 80m, ya que no es facil elevar un dipolo de 80m. son experimentos similares a los que comenta 4EOZ en la revista de la URE, pero radiando hacia el cielo...
== por otra parte, no puedo evitar comentar las interesantes discusiones filosóficas que ocurren en la lista de correo "HPSDR". estos temas son relevantes a los onda-larguistas, ya que hay disponibles ADCs de 250ksps y superiores, con una buena cantidad de bits (18, por ejemplo), pero que no exceden los 20 bits que se consiguen con el AKM5394A (delta 44, E-MU 1820m, etc) la duda existencial, es - mezclar y digitalizar con un adc de 24 bits (20 bits reales) - o digitalizar directamente con un adc de 18 bits (14..16 bits reales) == Robert McGwier wrote: > With the 200 kHz wide A/D's available in 24 bit packages such as the > AKM5394A that is being used in Janus, you will find it darn hard to > ever get the instantaneous dynamic range that is achievable by these > narrower band IF's available from the QSD (and its variants) where you > get something like 115 dB SFDR and NO NEED FOR ANALOG AGC IN FRONT OF IT > in the narrow band voice grade channel applications. No multi hundred > MHz A/D can give this kind of performance because of the near/far > problem so far as I have been able to find. You can get increased > dynamic range (not instantaneous) by getting processing gain through > downsampling/filtering. We are beginning to get interesting enough > parts that we might come close to this with these 16 bit (very > expensive) A/D's running at high bandwidths (such as Mercury, etc.). > > In the end, the criticism of the SDR-1000 is misplaced. Getting > performance that rivals much more expensive radios out of a design done > in a garage over a couple of years whilst talking to amateur radio > breakfast buddies on every Saturday about it and then helping to foment > the revolution we have seen it do and starting a major open source, open > hardware initiative along with proponents of GnuRadio is not something > to be dismissed without comment. To me, the SDR-1000 is one of those > little miracles that continue to make life interesting. > > If Gerald and Flex were to continue this form factor into future > radios, then I would say you have an argument. > > Bob > > I have a E-MU 1820m that has that same ADC. I wrote a Linux ALSA driver for it and I measured a noise level, with the balanced inputs disconnected, that made the resulting waveform accurate to about 20bits, the rest being noise. At this resolution, I think that the RF mixer would be at a higher noise level than this, so I don't see the point of much better than 20bits. I think that is also what the Janus developers found. With baseband ADCs running at 130Mhz now working to 16bits, probably 15 or 14bits real due to dithering, they are at least getting closer to 20bits. Baseband ADCs have other advantages over the SDR-1000 RF mixer, so there a arguments in both directions. 1) QSD has higher number of bits ADC, but have image rejection problems and noise introduced by the QSD clock and are cheaper 2) Baseband ADCs have potentially better filters, fft bins can be made smaller because there are more samples taken. Less detector noise as the ADC sample and hold circuits are less noisy. These are more expensive. James _________
