The "fat max" antenna - Page 1
Forum section: electronics / rf-microwave

author: A.Z.
author_rank: Super Contributor
timestamp: December 18, 2021, 04:54:36 pm
content: was seeking for ideas for a relatively restricted space antenna covering as much as possible of the HF bands (a friend in sweden has some HOA restrictions <sigh>)anyhow, stumbled upon this designhttps://webzoom.freewebs.com/g8jnj/FatMax%20Antenna.pdfdo you think it may be worth or... is it another "miracle" do-it-all antenna ?thanks

author: fourfathom
author_rank: Super Contributor
timestamp: December 18, 2021, 05:12:24 pm
content: It's hardly a miracle antenna, but it should be a decent adjustable vertical having untuned radials. You will still need a tuner somewhere, and low-loss coax between the antenna and the tuner. That 1:1 balun is probably a good idea as an isolator, even though the antenna is unbalanced. I suppose we could consider it at least partially unbalanced, given the (random?) radial design. Having the adjustable-length feature will certainly help reduce the SWR seen by the coax and tuner.Steel isn't the best metal for a radiator, but it's not too bad. My boat uses a stainless steel backstay as an untuned vertical (with a good seawater ground), and a wide-range tuner at the antenna base, and it performs well enough.

author: mag_therm
author_rank: Frequent Contributor
timestamp: December 18, 2021, 07:33:33 pm
content: A run of QuickField with steel strip 20mm by 0.2 mm at 14 MHz:A straight run of 1 metre length in free space, not considering radiation.The current density concentrates at the corners and thin edges.(Impedance /m)Steel, rho = 0.16e-6 Ohm.m Ur = 66, Steinmetz = 1.8Z = 0.43 +j39 OhmStainless steel, Ur = 1Z = 0.06 +j39 Ohm

author: cdev
author_rank: Super Contributor
timestamp: December 25, 2021, 09:15:53 pm
content: It's fairly straightforward to make a crank up tower out of telescoping tubing, such that it can be "cranked up" to attain a height of 10-12 meters or more. This is so it can spend most of the time close to the ground and can be raised when you want it at its highest. This is likely to allow you to have a long-lived tuned adjustable length vertical antenna.You could even screen scrape weather reports in order so that predictions of high winds or high winds recorded on your anerometer would trigger it to crank itself info its lowered position. This way you could be confident a sudden windstorm wouldn't take it out. To anchor it you could use a pipe perfectly vertical set in a mass of concrete. and three or more guy wires.

author: antenna
author_rank: Frequent Contributor
timestamp: January 03, 2022, 01:49:01 am
content: What about replacing the tape measure with a metal slinky? At least you get the added bonus of linear loading.

author: fourfathom
author_rank: Super Contributor
timestamp: January 03, 2022, 03:24:35 am
content: Quote from: antenna on January 03, 2022, 01:49:01 am

author: antenna
author_rank: Frequent Contributor
timestamp: January 03, 2022, 04:46:35 am
content: Quote from: fourfathom on January 03, 2022, 03:24:35 amAgreed, but 30+ feet dead vertical inside a 4" PVC pipe under HOA regulations? Good luck!

author: geggi1
author_rank: Frequent Contributor
timestamp: January 06, 2022, 10:03:31 pm
content: Check out the STEPIR antenna.They have 3 verticals types. BigIR 6m-40m (optional 80m coil), SmallIr 6m-20m, CrankIR 2m-80m.The antennas are very good if installed correctly with a propper groundplane.

author: latchesheyhey
author_rank: Newbie
timestamp: January 07, 2022, 03:19:07 am
content: Quote from: antenna on January 03, 2022, 01:49:01 amI agree

author: A.Z.
author_rank: Super Contributor
timestamp: January 07, 2022, 10:08:20 am
content: Quote from: antenna on January 03, 2022, 04:46:35 amwell, one may paint the pipe in a "neutral" color and put a "bird house" at the top

author: fourfathom
author_rank: Super Contributor
timestamp: January 07, 2022, 06:23:21 pm
content: Quote from: antenna on January 03, 2022, 01:49:01 amAbout that linear loading, is that really an advantage?A physical quarter wave radiator is going to perform better than a shortened antenna regardless the type of loading (distributed or lumped), and I recall reading that a physically short antenna performs better with a high-Q lumped loading coil, than a distributed lower-Q linear loading coil. At least that what some people claimed after analyzing 160-meter and below short antennas.This is probably based on practical implementation factors, and not theoretical ideal elements. Also isn't the radiation pattern a factor? I believe that as you shorten the radiator the pattern become more isotropic, which is probably why a loaded short vertical (even with zero-loss loading) won't perform as well as a full-length radiator (assuming you want low-angle radiation).Me, I usually just hang a dipole between two trees, or the house and a tree, trim it a bit as needed, and call it good. It's usually not aiming exactly where I think I want, but that's OK, I don't usually care who I talk to.

author: antenna
author_rank: Frequent Contributor
timestamp: January 08, 2022, 12:55:50 am
content: Quote from: fourfathom on January 07, 2022, 06:23:21 pmI would say it is still an advantage, because it still offers the ability to be drawn up with a rope. Of course a straight wire with a single loading element is better, but it was more about being easy to adjust, which that single lumped element match is not. There is no ideal solution in an HOA situation, other than mounting the mast on your vehicle or lawn mower or claiming its for TV reception under 47 CFR § 1.4000.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: January 14, 2022, 08:14:10 pm
content: In a clear area with conductive ground it should be fine.But in suburbia amongst houses with noise and indifferent ground then a quarter wavelength vertical with its bottom near the ground is likely to be a mediocre performer.Whether it is for the lower HF bands (which needs a good high angle component for closer in stations) or the higher HF bands for DX. It might also pick up a lot of noise on HF.A thin mast (which can be 10m high as used here) supporting a thin wire dipole or end-fed is likely to be better.

author: fourfathom
author_rank: Super Contributor
timestamp: January 14, 2022, 08:31:57 pm
content: Quote from: antenna on January 08, 2022, 12:55:50 amSorry, I meant "Is that really an antenna performance advantage?" You are right, it certainly does have some practical and mechanical advantages.