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]
