I'm not sure I agree with the exact numbers, Ian. I'm looking at the review from Nov 2015 QST (from the Product Review archive on www.arrl.org ) and it appears that the difference in phase noise between old and new synths is closer to about 3 dB (difficult to tell from the graph) beginning at offsets of *50 or 100 kHz*, not the 6 kHz you cited. At 6 kHz the new still beats the old by almost 20 dB!
So, while the old synthesizer certainly exhibits lower transmitted phase noise out beyond 50 kHz offset, the new one is within a few dB of it, and at 50 MHz both seem to meet the -130 dBc/Hz limit you cited. Al W6LX ________________________________ From: Ian White <gm3...@ifwtech.co.uk> To: elecraft@mailman.qth.net Sent: Wednesday, June 27, 2018 2:45 PM Subject: Re: [Elecraft] [K3] factory upgrade to K3(s) >A big reduction in receiver noise floor and a huge improvement in both >transmit and receive phase noise. That is far too simplistic. Anyone's personal definition of "the better synthesizer" will depend on what range of frequency offsets is more important for their particular type of operating. For HF CW in particular, phase noise at small frequency offsets is of paramount importance and I wouldn't argue with Don's report of "a huge improvement in both transmit and receive phase noise" - but *only* in that specific context. There are also several other advantages that are relevant to high-performance HF CW that could also justify upgrading to the KSYN3A. At close frequency offsets from the carrier, the KSYN3A does indeed offer a large reduction in phase noise compared with the KSYN3 (which itself was already good). But at wider frequency offsets, that situation reverses. According to the ARRL review [1], at all offsets beyond about 6kHz, the older KSYN3 continues to have a lower noise floor than the newer KSYN3A "upgrade". Performance at wider frequency offsets, 10-100kHz and beyond, is of much greater importance in VHF-UHF contesting. This due to a combination of factors. The strongest signals at VHF-UHF are often much stronger than on HF, due to the use of high-gain beam antennas; and also the weakest signals are *always* much, much weaker due to the lower levels of natural background noise. These two features stretch the requirement for dynamic range on VHF-UHF far beyond those for which most HF transceivers are designed. Anyone transmitting wideband phase noise has a much greater risk of raising the noise floor of many other stations across the whole contesting segment of the VHF or UHF band. Running the numbers reveals that anyone aiming to be a Big Gun in VHF contests has a responsibility to keep their wideband transmitted noise floor below about -130dBc/Hz at frequency offsets of 50kHz and more [2]. This can be a major engineering challenge, and the performance of the transceiver is almost always the most important building block. The KSYN3A just about meets the -130dBc/Hz noise floor target at frequency offsets of 10kHz or more... but according to the ARRL review [1] the older KSYN3 achieves it much more comfortably, with 10-15dB to spare. I have both a K3S and a very early-model K3. The K3S (with the KSYN3A, of course) is used for HF contesting where smaller frequency offsets are important. Meanwhile the old K3 is now used as a transverter driver for 144MHz and above - and for that particular purpose there are very good reasons *not* to replace the original KSYN3. 73 from Ian GM3SEK [1] http://www.arrl.org/files/file/ProductReviewsForDeb/2015/pr112015.pd f [2] https://thersgb.org/members/publications/video_archive.php?id=5703 Sorry, this talk is accessible only to RSGB members, but in a few words... G8DOH runs the numbers to demonstrate that the -130dBc/Hz target for transmitted phase noise is necessary to avoid raising the noise floor of other stations many kilometres away, and also many tens to hundreds of kHz away across the band, whenever their high-gain beams happen to be pointed at each other. That calculation assumes the UK transmitter power limit of 400W PEP output. For the US power limit of 1500W output, keeping all other assumptions the same, the target for transmitted noise floor would need to be better than -135dBc/Hz. The older KSYN3 can still meet that more stringent target but the KSYN3A probably cannot. >-----Original Message----- >From: elecraft-boun...@mailman.qth.net [mailto:elecraft- >boun...@mailman.qth.net] On Behalf Of Don Wilhelm >Sent: 27 June 2018 14:23 >To: hawley, charles j jr; Charlie T >Cc: elecraft@mailman.qth.net >Subject: Re: [Elecraft] [K3] factory upgrade to K3(s) > >Chuck, > >A big reduction in receiver noise floor and a huge improvement in both >transmit and receive phase noise. It is like getting a new transceiver. > >If you are strictly a casual operator, those qualities may not be >important to you, but if you are a DX'er or a contester, or otherwise >operate in crowded band condition, those things should be important >to you. > >73, >Don W3FPR > >On 6/27/2018 9:03 AM, hawley, charles j jr wrote: >> I decided to bypass the replacement of the synthesizers. Could you >describe the "huge" difference? >> ______________________________________________________________ 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 alor...@sbcglobal.net ______________________________________________________________ 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
