Wifi 2.4Ghz yagi antenna made from a mirror - Page 1
Forum section: electronics / rf-microwave

author: Robonz
author_rank: Newbie
timestamp: June 24, 2019, 05:32:21 am
content: Dave! do you want me to send you one of these in your mailbag? I made a wifi antenna out of a mirror using my laser cutter. It seems to work well. The yagi elements etc are the mirror which is conductive, I have nothing to test it with though. My signal went from 2 bars to 5 bars when I connected it so that was "my problem" solved. Check out the picsLaser cut in just a few minutes with some simple assembly. I did not even bother with a balun. I just hooked the loop directly to the shield and coax center.

author: hendorog
author_rank: Super Contributor
timestamp: June 24, 2019, 05:39:22 am
content: Nice!Not sure where you are, but if you can send me one/bring it over, I can test it on my VNA.

author: OwO
author_rank: Super Contributor
timestamp: June 24, 2019, 08:08:49 am
content: An even better test would be to put 10W into it and see whether it's lossy.

author: tautech
author_rank: Super Contributor
timestamp: June 24, 2019, 08:53:19 am
content: Your 'yagi' elements look equally spaced and not reducing in length further out from the active element.What Yagi calculator did you use to design this ?

author: Yansi
author_rank: Super Contributor
timestamp: June 24, 2019, 08:57:32 am
content: Not only does the spacing look weird, so does the element lengths. You can't use a simple yagi for a wideband Wifi signals. LPDA antenna would be more appropriate.Have you at least calculated the effective permitivity of the glass/air combo?VNA or it didn't happen!

author: tautech
author_rank: Super Contributor
timestamp: June 24, 2019, 09:03:18 am
content: Quote from: Yansi on June 24, 2019, 08:57:32 amThis ^^^Quote from: hendorog on June 24, 2019, 05:39:22 amYes your's as mine that you have to play with tops out @ 1.5 GHz.

author: borjam
author_rank: Unknown
timestamp: June 24, 2019, 09:13:13 am
content: Quote from: tautech on June 24, 2019, 08:53:19 amThe directors in a Yagi antenna are shorter than the main element but not decreasing in size, all of them are equal. The antennas widh decreasing element length are log periodics, quite a different beast.That said, that feeding point will be a disaster at 2.4 GHz. It would require a proper connector and matching network.

author: OwO
author_rank: Super Contributor
timestamp: June 24, 2019, 09:21:53 am
content: VNA won't tell you the full story if the elements are lossy; you could see a perfect match but nothing is radiating. I'm not sure how conductive the mirror coating is, but a power handling test (after you've verified the impedance with a VNA) is a good way to tell.

author: OwO
author_rank: Super Contributor
timestamp: June 24, 2019, 09:23:35 am
content: I have a VNA as well as 2.4GHz power amplifiers up to 20W. I can offer to test it out for you

author: Yansi
author_rank: Super Contributor
timestamp: June 24, 2019, 09:26:30 am
content: So how do you tell the difference between radiated and dissipated power?

author: tautech
author_rank: Super Contributor
timestamp: June 24, 2019, 09:27:31 am
content: Quote from: borjam on June 24, 2019, 09:13:13 amNot according to this calculator:https://www.changpuak.ch/electronics/yagi_uda_antenna_DL6WU.phpWack a few numbers in and look at director length.Sure not as pronounced reduction as log periodic yet Yagi still reduce director length, well at least in the ones I was gunna build for 315 and 433 MHz.J-Pole ended up much easier.

author: Robonz
author_rank: Newbie
timestamp: June 24, 2019, 11:30:41 am
content: Hi hendorog, I am in Auckland. Sure, I am keen to send one to you. You can contact me herehttps://www.edns.co.nz/index.php/about/The dimensions I used are from hereThey are probably totally wrong and the dielectric was not accounted for either. It would be nice to build one with proper dimensions after this one is tested. I just like to try stuff that I have not seen anyone do. All I can say is I get 5 bars on the wifi now, but that does not mean the antenna is doing the job. I have really crappy aliexpress coax, so that might be the actual antenna haha.Can someone offer calculated dimensions for acrylic as the dielectric?Cheers

author: borjam
author_rank: Unknown
timestamp: June 24, 2019, 11:37:03 am
content: Quote from: Yansi on June 24, 2019, 09:26:30 amWith Thermodynamics. Dissipated power means heat

author: David Hess
author_rank: Super Contributor
timestamp: June 24, 2019, 11:56:41 am
content: Quote from: tautech on June 24, 2019, 09:27:31 amThat depends on what the Yagi (or Quad) is optimized for. If it is gain which is common, then the element length and spacing of the directors will decrease. Sacrificing gain for maximum front to back and minimum side-lobes uses directors with a fixed length and spacing.Gain optimized Yagis are more sensitive to the tolerance of their dimensions making them more difficult to build.

author: Yansi
author_rank: Super Contributor
timestamp: June 24, 2019, 02:41:41 pm
content: Quote from: borjam on June 24, 2019, 11:37:03 amI do not think that can be made as a very quantitative measurement. Sure, the glass may get warm. But you won't get the dissipation factor that way.

author: borjam
author_rank: Unknown
timestamp: June 24, 2019, 02:53:43 pm
content: Quote from: Yansi on June 24, 2019, 02:41:41 pmNot that it's easy to measure accurately. But energy is either radiated or dissipated as heat. The extreme case is the dummy load, zero radiation and all of the energy heating the load.

author: David Hess
author_rank: Super Contributor
timestamp: June 24, 2019, 02:58:23 pm
content: Oddly enough, there is a very easy way to make *relative* measurements of the substrate losses in this case; stick a sample of the glass (1) or other prospective substrate into a microwave oven and measure the temperature rise.This works well for evaluating prospective materials for low loss to make capacitors and coil forms.(1) Not the printed antenna! That would be bad.

author: OwO
author_rank: Super Contributor
timestamp: June 24, 2019, 03:29:35 pm
content: Not that you need to make accurate measurements of dissipation anyways. You can easily tell with the finger test (after the RF is turned off) whether your antenna efficiency is <50% or >90%, and such a difference is only one or two dB and usually inconsequential in a communications system.