Sorry Freudian slip near the end corrected.. direct conversion changed to direct sampling ;-).
-----Original Message----- From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Chris Tate - N6WM Sent: Tuesday, April 26, 2016 9:08 PM To: Joe Subich, W4TV <li...@subich.com>; elecraft@mailman.qth.net Subject: Re: [Elecraft] Sherwood's receiver performance table updated Joet, interesting comments but perhaps misses a few conditions of the higher end Direct conversion systems. And thanks to Eric for allowing a relatively architecturally agnostic discussion on the reflector. My responses below. I will stick to my guns that both platforms have different advantages and disadvantages.. and its probably most accurate to leave it at that. While I do not know for sure, I suspect K9CT is using bandpass filters and stubs to prevent inter-station interference in his multi-multi operation just as he did when he used conventional transceivers. With properly designed bandpass filters, stubs and the preselectors in his 6700s he's not likely to have a severe overload issue unless he happens to be close to some high power AM stations (on 160 meters) and even then indications are that a good highpass filter and 10 to 15 dB of attenuation will resolve the problems with a 16 bit ADC. N6WM- Most certainly. I have operated a flex 6500 in one major multi-op contest at N6RO and a 6700 in another one. In both cases external filtering was used. It was unbothered by near field interstation interference any more or less than a K3, and I did operate 40m for WPX SSB (and nearly broke the station record for that band). I have not heard any reports of large multi-multi stations switching to direct sampling transceivers in areas of Europe where the 40 meter SW broadcast was a problem for many decades. N6WM- This is a good point I would be interested in hearing data or testing on this. The point is that direct conversion receivers need either good filters *ahead of the ADC*, attenuation or both to prevent problems. When one uses a Flex 6300 *which has no preselector*, Flex 6500 on multiple bands (which bypasses the preselector), an ELAD DUO which has no preselector, etc. one must make a choice between sensitivity and dynamic range. The ARRL lab tests show that, Sherwood's tests show that, Adam Farson's noise power ratio testing shows that, and other reviewers hint at the problem but they simply don't understand direct sampling well enough to recognize its limits when they see them. N6WM- ah a good point. These options are available in one form or another (external filtering) and of course we use this with our K3's or any radio in a multi. Also, many of the high end ones have 2 scu (6700) allowing dual band operation simultaneously without disengaging the band preselectors. One needs to understand the nature of direct sampling receivers and the way they react to overload to recognize the behavior but the test data is unequivocal. 16 bit ADCs are probably 4 to 6 bits "short" of being able to handle worst case signal levels while simultaneously providing maximum sensitivity (MDS of -135 to -140 dBm in 500 Hz) and fully broad band performance (multiple slice receivers on multiple amateur bands). N6WM- This does create some limits, but In the case of the 6700 you can have multiple slices on 2 simultaneous bands and avoid disengaging the preselectors.... how many does one need to operate at a time? 2 needed for SO2R. N6WM- these are different architectures with different challenges. The Direct conversion architecture is the new kid on the block and many of the features to enhance them are not there yet or are in an infant state. That does not say that the technology is unusable or if one or the other is better.. they are just different. Make no mistake.. I love my Elecraft K line. It has won me many contests and has served me well for (omg!) 8 years. I remember all the different mods we needed to add to the K3 in the beginning.. and the numerous software updates that fixed bugs and added features.... I also find the higher end Direct sampling systems fascinating as they solve a number of challenges I have run into over the years and they are on the fast track to coming of age. Also make no mistake.. despite the differences in architecture, challenges and advantages, both the systems in this email are competition grade transceivers. Check 3830. Ineresting stuff! ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to ct...@ewnetinc.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to ct...@ewnetinc.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
