SkyLoop antenna question - Page 1
Forum section: electronics / rf-microwave

author: A.Z.
author_rank: Super Contributor
timestamp: April 02, 2021, 01:40:56 pm
content: Hello folks, I had a bit of time in my hands and I decided to try running some 4NEC2 simulations on a "skyloop" (also called "lazy loop") antenna, the antenna is a square loop with a perimeter of about a full wavelength at the lowest desired frequency, in my case I designed the model (below) for an 80 meters band skyloop placed at 1/4 wave (10 meters) from ground, here's the model just for reference (and in case I made some mistake, one never knows)Code:CM ---------------------------------------------CM skyloop antenna :: https://www.qsl.net/4nec2/CM ---------------------------------------------CE' setup paramsSY freq=3.500 ' resonant frequencySY wave=(306/freq) ' wave lengthSY side=(wave/8) ' half side sizeSY hght=(wave/4) ' height from groundSY segm=81 ' segments in wiresSY feed=(segm/1) ' feedpoint position (fraction of side)SY wire=0.00125 ' wire radius' geometry of wiresGW 1 segm -side -side hght side -side hght wireGW 2 segm -side -side hght -side side hght wireGW 3 segm -side side hght side side hght wireGW 4 segm side side hght side -side hght wire' ground paramsGE -1GN 2 0 0 0 13 0.005' wires loadingLD 5 0 0 0 58000000' feedpoint positionEKEX 0 1 feed 0 1 0 0' test frequencyFR 0 1 0 0 freq 0ENnow (and here's my question), I ran some sweeps to check for SWR/Gain over the HF bands and the resulting graphs are shown in this imageif you look at the image you may notice that, at 200 Ohm feed impedance, the antenna is matched pretty well at its resonant frequency, but the curve raises when going up, the curve at 300 Ohm is a bit better, but then the one at 450 Ohm is almost flat, this could allow an ATU (which will be needed for multiband operation) to match the antenna more easily, so (here's the question), if one doesn't have a balanced ATU and neds to place a BalUn between the openwire line (ladder line) and the ATU, won't it be better using a 9:1 instead of the usual 2:1 or 4:1 ? And in any case why (or why not) ?Thank you !

author: cdev
author_rank: Super Contributor
timestamp: April 03, 2021, 03:26:34 pm
content: Loops are spectacularly great when they resonate at your desired frequency. But have never seemed particularly special to me when they didn't.even when connected to a low noise amplifier. Here you make a god point about impedance optimization for broadband use.Why not try an s-match as a broadband loop tuner? An s-match is a balanced tuner. A loop is a balanced antenna, what do you have to lose?

author: A.Z.
author_rank: Super Contributor
timestamp: April 03, 2021, 03:44:21 pm
content: Hi "cdev" thanks for your replyNow, you're right about using an unbalanced ATU like an S, L or T match, but then maybe my question was unclearlet's say one has an unbalanced ATU, so willing to couple it to the (balanced) ladder line coming from the skyloop, which balun would offer better results ?Judging from the simulation, a 9:1 would apparently be a good choice, but on the other hand, the literature suggests using either a 1:1 or a 4:1, hence my question

author: cdev
author_rank: Super Contributor
timestamp: April 03, 2021, 04:54:53 pm
content: 1:1 seems like a good start. I have a switchable balun (clone of elecraft bl2) which has 1:1 and 1:4, and I try to always start with 1:1 (unless I have the kind of graph you have.)Then I start with a higher impedance. There is always a big benefit to using a balun. I know that isn't very helpful..Quote from: A.Z. on April 03, 2021, 03:44:21 pm