Thanks for the explanation, John.
Im not an electronically educated fellow, merely just seeking the practical. A resolution to my post was provided in the suggestion that the apparent 1.1:1 SWR might be the result of common mode current. Sure enough when I installed a 1:1 current balun at the feed point of the antennas (2 perpendicular Inverted Vees with a switchable common feed point), the value went from 1.1:1 to 1.0:1 and the bottom of the SWR curves which also broadened out. Still that doesnt explain why the K3 was showing 1.1:1 while passing 1.0:1 information to K3EZ, or so it seems. I dont think that the K3EZ is measuring SWR rather merely posting information it is getting from the K3 no different measuring device or location. Perhaps it is a sort of rounding error. By the way, for those who havent come across it, K3EZ has the great feature of being able to step the K3 across a frequency range, momentarily key it, step again, etc. and plot in text an SWR chart a handy feature for working with an antenna installation. Following is a situation that perhaps you have the theoretical background to explain I have a full-size monoband vertical for 40 meters. Simple architectural aluminum tapering from 1 ¼ (?) in 6 telescoping sections. The radial field is designed to provide a 50 ohm match at the feed point 12 13+ radials. It is fed directly no matching device with RG-213 from the remote antenna switch about 50 away at my tower. The coax from the rig to the remote antenna switch is estimated to be ~ 50 in length. A lot of the time running K3EZ to sweep the band (typically 20 watts), it will indicate a 1.0:1 SWR from 7.0 MHz to 7.3 MHz in 20 kHz steps. Occasional deviation from one K3EZ run to another might be due to variations in moisture content of the ground or less than perfect connection to the vertical an uncommon situation. The K3 shows the same readings. Is this 1.0:1 SWR across the entire 40 meter band curious or remarkable? Dick KA5KKT ---------------------------------------------------------------------------- ---------- Hi Dick, Some numbers: using the K3 Schematic, "K3S RF Board" Sheet 2, Section B1. The power meter uses a series Schottky diode detector. The low reasonable resolution is about 0.3 VDC, or 0.3 * .707 = 0.21 Vrms out of the directional coupler. The Power for 0.21 Vrms is: 0.21^2 / 50 = .88 mW Assuming a 20 dB coupler 1:10 turns ratio, 0.88mW * 100 = 0.88W reflected power. Assuming forward power of 100 watts and 0.88 watt reflected power the return loss is: 10 * log(100 / 0.88) = 20.6 dB Using the calculator: https://www.allaboutcircuits.com/tools/vswr-return-loss-calculator/ 20.6 dB Return Loss computes to VSWR = 1.222 Therefore, the best lowest estimated K3 VSWR, assuming a 20 dB coupler, is about 1.2. Check my numbers. John KN5L On 7/27/18 9:58 AM, Dick Dickinson wrote: > I've noticed that I'm not showing a reading of less than 1.1:1 SWR on my > antennas per K3 SWR Numerical Readout. K3EZ will record 1.0:1 SWR in band > sweeps. > > Can the K3(S) Numerical Display show 1.0:1 SWR? If so, is there a likely > reason why K3EZ will show 1.0:1 while my K3 will only go as far down as > 1.1:1? ______________________________________________________________ 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
