Using your Xiego X5105 as an Antenna Analyzer
2018-09-10 If you play with radios much you realize that you need some way to "look" at your antenna. It's one thing to fiddle with a manual tuner or touch the tune button on an auto tuner and get on the air. It's another thing to have some idea of what you antenna is really doing. Particularly with a resonant antenna such as a dipole or inverted vee, or even an end fed resonant wire, it is helpful to know what it's actual resonant frequency is and its impedence (resistance if actually resonant) at that frequency. We've all had the experience of looking up the formula, calculating and cutting the wires for our dipole and then not having it resonate due to height, wire type or size, nearby things and just the fact that formulas can't take into consideration the real world we have to deal with. Now what.
The "best" and probably most expensive answer is a good antenna analyzer. While recently preparing for Field Day I borrowed my friends MFJ analyzer as I trimmed, lengthened and otherwise fussed with a fan type 40/20 meter inverted vee and a trap type 40/20 inverted vee. Arguably the most helpful thing about using it was the ability to plot a graph of the antennas after each change. That allowed me to not only see at what frequency it was resonant, but the useful bandwidth. With that information it was "easy" to see whether I needed to lengthen or shorten the elements. Enter the SWR feature of the Xiegu X5105 QRP transceiver.
My primary station antenna is a full sized G5RV. It is of course a non resonant antenna, requiring a tuner for most bands. And I've always used either a manual or auto tuner with it. I love the antenna. It just works dependably every time on all bands making life simple! Without hesitancy I recommend it to everyone. If you are only going to have one antenna, you can't go wrong with a G5RV. But what does it "look like" to your tuner or rig?
Below are two shots of the SWR sweep screen on my X5105. The left one shows the SWR curve on my G5RV on 20 meters. It stays below 2:1 across the entire band. I don't even need a tuner on that band apparently.
The right hand picture is a screen shot of the X5105 SWR across the 40 meter band. It looks to be around 4:1 at the lower end of the band and down to about 2.5:1 at the upper end. A tuner is probably needed on 40 meters.