To help make this discussion clearer, there is no problem about referencing the original article [1]. The author, SM5BSZ, has published it on his website for everyone to see, because this topic of wideband noise from transmitters needs to be much more widely known.
<http://www.sm5bsz.com/dynrange/dubus313.pdf> The wideband noise in question is composite noise (meaning both amplitude noise and phase noise) at wide frequency separations from the main signal. In simple terms, phase noise comes mostly from the synthesizer but amplitude noise can come from both the synthesizer and other sources as well. It's those "other sources" of amplitude noise that can prove to be important. In many modern transceivers the TX signal starts out at a very low level, and the low-level TX amplifier stages need to be designed like a receiver LNA to avoid adding unwanted noise. Careless designers forget this... and some make even worse mistakes. Elecraft owners can relax. The K3 comes top of SM5BSZ's TX noise table with a measured level of -126dBc (in ARRL's normal reference bandwidth of 500Hz). This is outstandingly good, 15-25dB better than the chasing bunch which includes the KX3. The difference between the K3 and the KX3 reflects the completely different hardware architecture of the two radios, but there is no shame in the KX3 coming 6th because its transmitter noise performance is still good enough for almost all practical purposes. Dave's concern is that high-level TX noise sidebands can cause problems to other band users. HF operators never notice this problem because TX noise is buried beneath other band noise; but it can be a very real problem on VHF and microwaves where the background noise levels are extremely low but signals can sometimes be much stronger than on HF. This places extreme demands on dynamic range - not only in the receiver (which we hear a hear a lot about) but also in the transmitter. The KX3 qualifies as 'good enough' because its transmitter noise sidebands are unlikely to affect anyone else's noise floor unless the main signal is stronger than S9+40dB... and the K3 is another 20dB better than that. The people who really should be worried are the owners of "Brand F", two models of which measured about 25dB worse than the KX3, and one model was almost 50dB worse than the K3. (In case that number slid by you, 50dB is also the difference between 10mW and 1kW!) The amplitude noise sidebands of "model F" at +/- 350kHz are so bad that they can clearly be seen with an old, noisy spectrum analyser... and that means VERY bad indeed. SM5BSZ particularly criticizes the ARRL reviewer's statement that "Overall, the composite noise output as shown in Figure 3 is low" when that number was way higher (30-45dB) than ARRL's own measurements of other transceivers. Bottom line: Elecraft users can go back to sleep :-) [1] For full disclosure, I am a volunteer editor for DUBUS magazine (www.dubus.org). Copyright of articles published in DUBUS remains with the original authors, so they are free to publish in other media as well. 73 from Ian GM3SEK >-----Original Message----- >From: [email protected] [mailto:elecraft- >[email protected]] On Behalf Of Dave >Sent: 21 December 2013 00:48 >To: [email protected]; Elecraft Reflector >Subject: [Elecraft] Transmitter performance > >I have recently received a copy of a publication known as DUBUS (for those >outside of Europe, this is a technical publication dedicated to VHF, UHF and >SHF equipment design and operating) and one particular article caught my >eye. The reason being that I'd suffered from some wide bandwidth signals >from a semi-local beacon during a band opening on 23cm where the >transmitted >signal from the beacon could be detected over a large frequency spread. >The >issue, in this case, was apparently down to the power supply used by the >beacon. > >Now, in the article in DUBUS 3/2013 (Vol 42) a description of potential >problems for various Amateur radios from the quality of their transmissions >was discussed and a table of 'good', 'reasonable' and 'poor' results from >tests taken from ARRL and Sherwood Engineering data (which I know >people >from Elecraft are often more than happy to quote, so I would guess it passes >some engineering muster...) were presented showing not only the receiver >performance, but the transmitter performance as well. > >Without wanting to quote the whole table (there may be copyright issues of >course) but the K3 came top (distant cheering heard from Aptos, CA) but the >KX3 came 6th. The criteria for the ranking being a "TX Wide" measurement >in -dBc and the K3 scored 128@100kHZz or 120@360kHz - which only >seemed to >be included as two radios from a rival company were both ranked at the >bottom of the table and could muster no better than a measurement in 300 >and >350kHz bandwidth) but the KX3 scored 107@100kHz. > >The reason that this is important is that, in an area where people are >tightly packed together, someone using a transmitter that generates >significant wide band noise within a particular Amateur band is not the sort >of neighbour that you want to have next to you on the VHF/UHF/SHF bands. >You might be listening on, say 144.050MHz but if they are transmitting on, >say, 144.350MHz then their wideband noise will affect you and, as is stated >in the article, they may not even to be transmitting to generate significant >signal levels. > >So, to my question. As I'm interested in VHF/UHF/SHF more than HF, why is >the KX3 transmitter performance worse than the K3 and, other than selling >the KX3 (which I'd prefer not to do) and buying a K3 (which is attractive, >but financially a bit of a problem) what, if anything, can I do to improve >the 'TX Wide' performance of my KX3? > >Dave (G0DJA) ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
