where is the ground plane in wifi router antenna?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KM6BSQ, Dec 1, 2019.

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  1. NH7RO

    NH7RO Ham Member QRZ Page

    Inside one's computer---just cleaned many , many rascals out of mine earlier today---from sites I've never heard of or knowingly visited.

    I only trust home-made oatmeal-raisin or the star anise-pecan cookies my xyl makes these days.

    (I still have to be careful with the crumbs which can get lodged in the wireless keyboard, though)
     
  2. AD5MB

    AD5MB Ham Member QRZ Page

    what little I know about wifi antennas, in PDF form
     

    Attached Files:

    2E0CIT likes this.
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    Not much of an option anymore with MIMO as they require 2 to 6 antennas.
     
  4. KM6BSQ

    KM6BSQ Ham Member QRZ Page

    Thank you for sharing, I did a similar thing a while ago and did not notice any measurable improvement. It looks like you are quite satisfied with your upgrade, why does it provide an improvement?

    I'd like to test my understanding of this, please advise

    1. It does not look like the foil around the vertical dipole is in the precise parabolical shape, neither it looks like the dipole is in the focus of such sudo-parabolical reflector. There will be some reflection, of course, but it's not clear if it would make any noticeable difference. OK, so it's not a reflector to the antenna. It might be a reflector for RFI coming from the "rear", but since the foil does not appear to be connected to the dongle groud or the PC chassis it not only reflects RFI it also emits RFI in all directions, including the dipole. In other words, it's a poor RFI shield as well.

    2. I'm going to assume that dipole legs a precisely cut for wifi freq. When you soldered a bit of coax to the dongle you disrupted the designed feed point impedance of the WIFI dongle, most likely increasing SWR of the antenna system. Since TCP/IP is two ways it should hurt your transmissions and lead to a lower speed.

    3. Dipole orientation. Most likely your neighbor router's antenna(s) are vertically oriented. Perhaps when you put your dipole vertically it got +3dB?
    I also think that due to multiple reflection/refraction from walls and objects wifi signals become randomly polarized so any specific antenna orientation would not make much difference either.

    Why does it work better than the dongle alone?

    I can offer only one guess - you moved it a bit away from PC induced RFI and this alone somehow overcompensated for all the shortcoming above. There could be a test to this theory - one could get a USB cable extender and place the dongle couple of ft. away.

    Of course, 2E0CIT, I don't expect you to do anything, just trying to learn.
     
    Last edited: Dec 3, 2019 at 5:39 AM
    2E0CIT likes this.
  5. WA7F

    WA7F Premium Subscriber QRZ Page

    I’d like to get WiFi out to my existing tower (100’), to the shop (300’) and then a future remote tower location (1000’) from the shack without breaking the bank. There are a few patches of pine trees on the 1000’ haul. The connections need to be fast enough to support remote transceivers.
     
  6. KX4O

    KX4O Ham Member QRZ Page

    Good point. So too is anyone claiming antenna gain in db.
     
  7. KS2G

    KS2G Subscriber QRZ Page

    For sure.

    Our local public library has wifi ... and my phone connects to it when I'm in a gas station that's across a 4-lane road from the building ... about 100 yards. ;)
     
  8. KF5FEI

    KF5FEI Ham Member QRZ Page

    Mikrotik makes some good, inexpensive WiFi and router stuff. However, it is not easy to configure like consumer units. Here is a link to their catalog:

    https://download2.mikrotik.com/catalog_2019.pdf

    There are distributors here in the U.S. -- we've used them to set up links between field day sites that were shielded by buildings, etc...
     
  9. 2E0CIT

    2E0CIT Ham Member QRZ Page

    Thanks for the feedback Igor, some excellent thoughts there, I claim no expertise in antennas but, like you, always very keen to experiment and learn!

    1) I chose to make a 90 degree 'Corner Reflector Antenna' from the foil and dongle, the reason being that I'd read this article:

    https://qrznow.com/corner-reflector-antenna/

    -noting that: -(unlike a parabolic reflector) spacing and angles are not too critical in achieving some gain and it's far simpler to make in a hurry from a pie dish than a parabola! A parabolic dish would have to be BIG, -and I can't eat a pie that size!

    2) Yes, I cut the dipole legs to size for wifi frequency however I did not add any coax. The coax was already there inside an articulated plastic radome projecting from the usb dongle and it was configured as a 'Coaxial Dipole Antenna', i.e. the centre conductor of the coax projected further than the shield of the coax. I couldn't see any ferrite in place to choke the coax shield at the appropriate point or anything that looked like a sleeve balun as is necessary with Coaxial Dipoles, so I decided to reconfigure it as a 'normal' balanced dipole to match the paper I'd read (above) on Corner Reflector Antennas. I had also read about difficulties people had trying to get Coaxial Antennas to work properly and judged that the one manufactured with the cheap dongle was maybe not designed or built as well as it could be..

    Whether I created an impedance mismatch by doing this or actually improved the impedance match I don't know, but since making this wonderful craptraption the wifi speed has risen from 20 Mbps to circa 39 Mbps.

    I did think about polarisation, so attaching a usb-usb connector cable with ferrites, rotated the antenna, -it gave marginally, but consistently, better speeds when vertically polarised. This was the same whether it was close to all my rf sources in the shack or several metres away from them. Pointing the antenna in any direction other than the direction of the wifi source gave much lower speeds.

    And don't forget that I also blu-tacked a small sheet of al foil on the wall about 10 cm behind my router a couple of rooms away, this maybe raises the signal strength in the direction of the shack.
    We learn from failed experiments as much as we learn from successful ones, they're always a mix of frustration and fun. I was lucky with this one. :) Good luck with yours and please share them!

    73, Jeff
     
    Last edited: Dec 3, 2019 at 3:41 PM

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