Goofing around with a 30 dollar vector network analyzer i got around ThanksKilling on ebay when I got really high on edibles.

Im an absolute rook when it comes to RF, RF theory, antenna building, etc. i follow calculators that others have created for rookies like me. That said, there is a water tower about a half mile from my house that has a repeater for the local counties that are tied in to a EMS system. im working my way towards having a setup to follow the trunked radio system, decode it and allow me to listen to it. im “teaching” myself enough CAD to be passable when nobody who knows more is in the room, and am making a frame for the antenna so I can print it in ABS and mount my antenna outside eventually.

i followed a calculator i found online, and built

a Moxon tuned for 853mhz which is the repeater’s frequency. I built it out of some rg6 that i stripped the center conductor from and a piece of rg58 with an SMA connector. i made a dimension jig, measured the reflector and elements, soldered everything together and then taped it to the jig I had my measurements on. Calibrated the VNA, and hooked it up to my antenna.

This is the results - my first photo is a sweep from 50khz - 1ghz. my VNA is only 30 bucks after all, so it has a very small resolution. I can do a broad sweep with about 100 data point, find its harmonics, then narrow down sweeps to get finer details. my second photo is were my SWR was the lowest. I didnt quite nail it, its resonant a little north of 853, which is my intended frequency, but even still im at 1.2 swr which is good as to my understanding. i had the logmag function set to a different input on the VNA so the measurement here is wrong in the second screenshot. it is correct in the first one.

SWR, I think t,his is a ratio of power transmitted to power broadcasted at the antenna. 1:1 is ideal. here its about 1.2:1 which is pretty good. needs to be under 2.5:1 as ideal. logmag shows what frequencies my antenna is good for lower -dB is better, here its tuned to about 750mhz-875mhz. everything below and above that is pretty well rejected. I think. like i said, im a rookie. im watching all sorts of stuff and reading everthing i can, because i want to test for my Amateur Technicians license next year. i imagine antenna theory and the like ties in to this somehow.

anywway, i did a thing, and wanted to show someone. anyone who knows more than me and feels like correcting what i got wrong please do so, but please be kind. Im just starting to feel like im getting the hang of the smallest thing, and dont want to be discouraged too badly.