It ends up that John KN5L gave a thorough treatment to the topic in this thread (might need to be a member of the KX3 Yahoo Group to read): https://groups.yahoo.com/neo/groups/KX3/conversations/topics/5869
73, Barry N1EU On Thu, Nov 3, 2016 at 4:08 PM, Ron D'Eau Claire <[email protected]> wrote: > You ask a commonly asked question. And, as usual, no responses so far. > > I can't give you an estimate either because first, the losses are highly > dependent upon the impedance transformation. You'd need to characterize > that > doublet and feed line (the length of the feed line is important) to see > what > impedance it presents to the ATU. > > Then you need to measure the ohmic losses in the ATU inductors, wiring and > connectors. Dielectric losses may occur but with modern gear they are very > tiny at HF. > > Finally you calculate the currents flowing in the ATU at each impedance > transformation required to achieve a match to your feed line so you can > calculate the losses based on the resistance of the wires, inductors, and > connectors. > > Personally, I accept the idea that an L-network (which all the Elecraft > ATUs > use) is highly efficient and leave it at that. > > If I were really inclined to actually measure the loss, I'd first measure > the RF power output into a stable 50 ohm load without the ATU in the > circuit. Measure with an external wattmeter at the load as well as the KX3 > output power indicated. > > Then I'd breadboard another L-network with a variable cap and variable > inductor, connect it to the 50 ohm load and to the KX3 output, transmit and > adjust the external L-net (not the KX3 ATU) for a 1:1 match. In that way > you > have created a known dummy load that presents the same complex impedance to > the KX3 as your antenna system. > > Now you can transmit at the same power at the KX3 as before and see what > the > power is at the 50 ohm load. Actually, you will be seeing what the power is > after passing through both matching networks. > > My guess is that you'd find the total loss so low you won't be able to read > the difference on the two power meters. > > A more direct approach would be to isolate the ATU in a very well insulated > enclosure, transmit, and measure the temperature rise until it stabilizes. > You can then calculate how much energy is being dissipated by the ATU and > becoming heat. That requires the ATU be carefully isolated from the rest of > the KX3 and be in a very well insulated enclosure to avoid loss of heat to > the environment, something not practical to do with a KX3. It is, however, > a > valid way to determine losses in external devices like an RF transformer > (e.g. "balun"). > > I suspect this explains why few (if any) Hams bother to make the > measurements. > > 73, Ron AC7AC > > > > > > -----Original Message----- > From: Elecraft [mailto:[email protected]] On Behalf Of > Barry > N1EU > Sent: Thursday, November 3, 2016 7:20 AM > To: elecraft; [email protected] > Subject: [Elecraft] KX3 tuner loss? > > I'd appreciate knowledgeable estimates of the loss in dB through the KX3 > ATU > when working into a 44ft (NorCal) doublet fed with twinlead, with or > without > a BL2 balun inline, on 20/17/15M. > > Thanks & 73, > Barry N1EU > ______________________________________________________________ > 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 > Message > delivered to [email protected] > > ______________________________________________________________ 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 Message delivered to [email protected]
