At 01:30 PM 4/12/2007, Lee A Crocker wrote: >You know it's funny but I think it's a bargain at $2500 just based >on the specs in the add. I already know what the SDR-1K will do >and what PowerSDR will do so all I have to do is speculate on what >systems MUST be there in order to meet the features provided in the >add copy and I see an overall fantastic value. I may not know the >exact particulars but I can tell enough to be very excited about >this radio at this price point. I presume the exact particulars >will be released as soon as Flex is satisfied with their validity. > >Icom for example claims +40dB on their intercept point for the >IC-7800. That number is really a fabrication and is arrived at by >gaming the ARRL testing methodology.
QEX has run a series over the past 3 issues discussing just such things. The problem of testing modern multichannel radios with signal processing is an issue is faced by more than just amateurs. Properly specifying and testing amplifiers for modulations such as COFDM (especially when the amplifier isn't being run in linear mode and is deliberately run with some clipping for improved efficiency) is quite a challenge. Simple multi tone measurements, while easy to implement with 1940s technology, and adequately characterizing systems of that era, aren't necessarily appropriate for modern systems. This has been a problem as far back as carrier telephony. For that matter, "harmonic distortion" or "third order IM" are based on a fairly simple model of deviation from linearity (i.e. a cubic term instead of purely linear). That's a good conceptual model for a continuous system but not for one that is "discrete" (like one that uses sampling, either in time or amplitude) There's a variety of newer (and some not so new) techniques, such as putting in a noise signal with a "notch" in it and seeing how much power shows up in the notch. There's also clever schemes with moderately complex signals (trivially generatable digitally) that allow you to measure things like AM/PM, various distortions, etc. Such is life at the bleeding edge of technology.. but hey, that's what we're here for, "to advance the radio art" Jim, W6RMK _______________________________________________ FlexRadio mailing list [EMAIL PROTECTED] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
