KV9U wrote: > Interesting comments. It always seems that there is nothing new that > is totally perfect compared to existing equipment due to the > tradeoffs that often occur.
Tradeoffs are a central part of engineering. >The SDR-1000 does look really interesting > as a general purpose receiver that has some excellent IMD numbers and > may be used (with the right programming) for reception of DRM, etc. > My long term plan is to purchase the rig, although I never buy too > early on the "bleeding edge." > > The latency issue is a drawback that does not seem to be solved at > this time. It is not going to compare with rigs that have superior > QSK (e.g., Ten Tec). But most of us do not really find QSK all that > compelling. Incidentally, even Ten Tec has had difficulty with QSK > quality with their Orion series rigs which are heavily SDR designed. > > Is it fair to say that the carrier suppression is going to be lower > than conventional rigs due to the DC (Direct Conversion) design? I believe it depends on the circuitry, and frequency of operation. > I might mention, that some time back, during an ARRL product review > (can't remember the rig), the comment was made that, if anything, the > DSP rigs tended to have unusual Dynamic Range characteristics that > may perform better in actual use than in just looking at the test > numbers. I am not sure if I accept that fully, but it makes one > wonder. Although the ICOM IC-7000 has some of the worst IMD DR of any > recent rigs, many users really like the rig and find it performs > fairly well. I don't think so. The Quadrature Sampling Detector shows such impressive numbers because "the mixer" is nothing else but a chopper with high speed switches that accepts signal amplitudes up to almost Vdd on the switch chip, say, 4 V peak to peak wit 5 volts. I used 4066's on 40 meters with 12 volts and it works impressively well in a band full of high power broadcast stations. On 30 meters, 4066's begin to be too slow and the results begin to be flaky. I could not get faster switches. But dynamic range is not a property of the software, it is the particular hardware solution of the SDR1000 and Softrock 40. If you change the mixer to baseband, you are stuck with its properties. If you alter the gain distribution, power supply voltages, etc, it all is going to change. What can be warranted in an SDR is the mathematical treatment of signals in the digital domain, after they are digitalized. The quality of the ADC's also counts. And mathematical treatment costs latency, because processing and particularly, filtering, is done with memorized samples added up with certain coefficient ratios. On a radio there will always be parameters defined by the hardware, and signal treatments that are only possible one way or another, that is, the analog way or the digital way. An SDR is a mixture of things, and the quality of the whole results depends on the quality of the components of the system, that is, hardware and software. The results obtained by inadequate performing hardware can hardly be improved on the digital domain. You need clean signals to obtain clean results. Attenuators and good filters are still needed and 16 bit ADC's cannot go beyond some 96 dB's (roughly 2 ^16 times). To obtain a larger dynamic range you need more bits, or some trick like controlled attenuation before the ADC. It depends on your application and what you are willing to accept. > Because the SDR is truly open source software, it is exciting that > this will not be a closed proprietary design that we have seen from > pretty much everyone else. And that includes the potential of digital > mode operation. While there is nothing yet that is so compelling you > just have to have one, that may eventually come about depending upon > your interests. A PC based design depends on the latencies and delays imposed by the operating system. That is what makes the HPDSR so interesting, because it will have an operating system taylored to a radio, and not a general purpose OS like Windows on a PC. On Linux, a real time kernel MIGHT give some improvement to the tasks defined to be done on real time on a particular combination of CPU, memory and motherboard chipset. Nevertheless, the concept of doing the radio software tasks on dedicated hardware and software is a winner, it is "distributed computing", sort of what we had with TNC's and early PC's. Those who wanted to avoid having a TNC and wanted all to be done on the PC (Baycom style, remember?) had to have a more powerful PC. Nowadays, PC's are far more powerful, nevertheless, that principle is still valid, and might apply to SDR with the available computing resources. > The one thing that I really like about this kind of community > supported design is that it does not become rapidly obsolete in terms > of upgrades and improvements. I purchased a Ten Tec Pegasus around > 2000 or so and in only a couple of years, Ten Tec abandoned any > further updates to the rigs software, including the mediocre > interface. While you could buy several third party programs, the cost > made it ridiculous and contrary to the promotions of how this rig > would be able to be updated for a long time. So having learned my > lesson, I am very cautious about future claims by any manufacturer. > It has to be something that it has operating now and is relatively > bug free. Nothing beats a wise, informed choice....You need truthful / trustworthy info to achieve that. > We saw this with other digital products in the past, such as the > ultra expensive AEA DSP 2232 interface. Lots of promises, but it > never really delivered for the kind of money being asked. Partially, > because they could never cross license other digital modes, but they > also did not try and develop their own either. My point of view is that one of the things that led to the demise of packet on HF was using 300 baud as the ONLY signalling speed. It created a de facto standard that was failed and could only work well in very specific situations, and nothing was done on a timely manner to save it, not even by the software TNC writers, because it might not find use against a de facto standard, sort of a Catch 22 situation. On packet, the sublayer on Layer 1 that defines modulation and coding should have been substituted a long time ago for something better. After all, AX.25 defines Layer 2, not Layer 1. The manufacturers did nothing effective (that I know about) to improve it, and the day arrived when AEA declared bankrupcy "because Internet had spoiled packet radio", and many people saw the sinking ship, no solutions, and fled the ship. I believe it is wrong to blame the Internet for the inactivity on that front. I am afraid it went unattended too far beyond the point of no return. > 73, > > Rick, KV9U 73 de José, CO2JA PS: On a previous post, I mentioned power mosfets as mixers. I meant high speed POWER RF MOSFETS, like the ones used on some high end russian radios. KP905 comes to my mind now... __________________________________________ XIII Convención Científica de Ingeniería y Arquitectura 28/noviembre al 1/diciembre de 2006 Cujae, Ciudad de la Habana, Cuba http://www.cujae.edu.cu/eventos/convencion Need a Digital mode QSO? 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