Hi Stewart, The KAT3, like all wide-range ATUs, has significant stray reactance, especially on the higher bands. When you tuned it into 50 ohms, you created an L-network on each band that tunes out this reactance--at that one impedance.
In your test, the KAT3 is between the K3's SWR bridge and the LP100, so the two bridges are looking at different points in the network. So changing the load Z to 25 ohms affects the two readings differently. The disproportionate error on 20-15 m reflects the nature of the KAT3's strays. On these bands, the stray-cancellation values that it automatically finds results in an L-network. On still higher bands, it may look more like a Pi network, which could explain why your SWR error delta is lower on 6 meters. On the lower bands, the strays are less significant, so the readings match. If you removed the KAT3, the readings would be in closer agreement. 73, Wayne N6KR ---- http://www.elecraft.com On Nov 4, 2009, at 8:44 AM, Stewart <stew...@baker.nildram.co.uk> wrote: > Hi, > Now traffic on the new K3 Macro functions has somewhat died down, > I would like to raise again the issue of the K3's SWR measurement > accuracy. > > I did some tests using dummy loads and a LP-100 meter as follows. > > The dummy load is a precision 100W one which I measured with a VNA > and has a VSWR of <1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR > I used another dummy load (not quite as good) in parallel. > > The K3 output was from ANT1 using the internal ATU. The ATU was > automatically tuned to 1:1 on all bands. > The results I got for 2:1 VSWR are as follows:- > > LP-100 K3 > 160 1.99 1.8 > 80 1.99 1.8 > 60 1.99 1.8 > 40 1.95 1.8 > 30 1.97 1.6 > 20 1.97 1.4 > 17 1.97 1.3 > 15 1.96 1.2 > 12 1.96 1.5 > 10 1.96 1.4 > > As can be seen my K3 SWR indication consistently under reads. > However, it really gets bad on 20,17 & 15. > > From previous replies I understand that this under reading would > be compensated for in the firmware, sometime in the future . > > Is this still on the list of problems to be addressed ? > > 73 > Stewart G3RXQ > ______________________________________________________________ > 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 ______________________________________________________________ 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
