Yesterday, K9YC wrote: > >Likewise, we must qualify the dynamic range of the measurement system -- >when does it begin to contribute distortion due to its own >non-linearity. This is what K2XT ran into in his tests. > That error did not affect my tests. I re-ran the same tests today and reconfirmed that, across a 60dB range of input levels to the SDR-IQ, the measured IMD3 levels change by less than 1dBc.
Making further tests at 100W PEP, I measured IMD3 levels close to -30dBc at 1.9MHz and -27-28dBc at 14.2MHz... but then deteriorating with frequency towards -20dBc at 28.5MHz. However, I do confirm Jim's measurements that the IMD3 values at the 50W level are at least 15-20dB better. When driving a PA at 30-50W, the K3 or K3S will almost never be the limiting factor in determining IMD. Responding to Don's point: all of these IMD measurements were made at an indicated supply voltage of 14.5V. Following discussions in this forum some years ago, the supply voltage had been deliberately increased to help improve the TX IMD performance. I must repeat the warning that these measurements were made with a 7-year-old KPA100 module in a new K3S so they may not be representative of recent examples of either the K3 or an all-new K3S... but in other respects the trends are clear. 73 from Ian GM3SEK >-----Original Message----- >From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of >Jim Brown >Sent: 01 September 2015 19:28 >To: elecraft@mailman.qth.net >Subject: Re: [Elecraft] K3S IMD Questions > >On Tue,9/1/2015 10:44 AM, Ian White wrote: >> Today, anyone can make 2-tone IMD measurements using a modern SDR >and a >> little care in setting up the input levels. The K3 itself provides the >> 2-tone test signal (CONFIG:2TONE On). > >Yes and no. Let's not forget that the response of any measurement is the >combined response of both the measurement system and the device under >test (DUT). > >An important test of any spectrum measurement system is its frequency >resolution, which can be tested by its response to a steady unmodulated, >unkeyed carrier. Like slide #8 in > >http://k9yc.com/P3_Spectrum_Measurements.pdf > >Likewise, we must qualify the dynamic range of the measurement system -- >when does it begin to contribute distortion due to its own >non-linearity. This is what K2XT ran into in his tests. > > >On Tue,9/1/2015 10:54 AM, Don Wilhelm wrote: >> Anyone who does such testing should also include in the report(s) the >> power supply voltage as seen by the K3S alternate VFO B display. >> Lower power supply voltages will have worse IMD than voltages that are >> higher. >> Running the K3 or K3S with a power supply voltage above 14.3 volts >> will improve the IMD substantially. > >Yes, the K3 and K3S are a bit cleaner with higher power supply voltage. >K6XX showed this in a presentation to NCCC a few years ago. It's on my >website. > >All of my testing has been done with power supply in the range of 12.3 - >12.6V. > >73, Jim K9YC >______________________________________________________________ >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 gm3...@ifwtech.co.uk ______________________________________________________________ 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
