antenna-theory.com

[Matthew]

When I was a kid I recall someone telling me about a place in the valley where they put up a big antenna that was up over the hills, and passively radiated that signal down in the valley. This may have been urban legend but the idea stuck with me.

I have set up a little electronics shop on my property. Sadly, it is situated directly behind a metal morton style building. You can not see the electronics shop from the house.

I would like to get decent WiFi out there. My first attempts were with higher powered routers and more directional antennas. This did not work, though the road we live on goes up hill and I got great WiFi on my smartphone a quarter mile away once the elevation got higher than that building.

I tried a commercial WiFi repeater. That slowed everything in the house down and did not work much better. I believe that may have helped had it been mounted on the roof of the metal building, but it was an indoor rated device and lack of a dry place to put it and no power on the roof made that one a no go.

I keep coming back to the passive repeater idea. This has a lot of advantages.

1) It is inexpensive as in free
2) No power
3) Weatherproof
4) Will not slow the main network down.
5) Should also work for other 2.4Ghz things. My phone system for example.

My idea is to build two WiFi Yagi's out of 3/4" PVC pipe and stainless TIG welding filler rod. I would join he antennas with a very short (perhaps 24") length of 300 ohm TV twin lead. The two antennas could share the same mast.

Some questions..

1) Does this sound likely to work. I know there will be loses. I am trying to minimize them.

2) Do the materials I want to use sound reasonable? They are things that I have on hand.

3) I realize that the stainless tig rod is larger in diameter than ideal, but I am not sure how important that is. I tried the wifi with a Chinese yagi and that used tubing that was considerably larger in diameter than the stainless. I think the stainless is 1 or 1.6mm in diameter.

4) The line connecting the Yagi's will be short. I believe the dipole that drives the Yagi's should be around 300 ohms. The only better choice I can think of for the interconnect might be ladder line and given the very short length, I doubt it would make all that much difference unless tinlead is truly awful at 2.4 Ghz. I have not seen it rated at anything over TV UHF so I really have no idea.

I am looking forward to thoughts and ideas....

[admin]

If you have good impedance matching, it should work (i.e. antennas impedance close to 300Ohms so you don't lose a bunch of energy from reflection)...or at least I'm not sure why it wouldn't increase the gain in the direction you are trying to send the power to.

Have you thought about just making a reflector to bounce the signals in the direction you want them to go?

[Matthew]

I have not really thought about a reflector. What would that entail?

I figured the yagi to yagi was a good idea because I know there will be losses and this way I can use an antenna that is very efficient to receive the signal by pointing it directly at the house, and I can focus the re-broadcast signal similarly, directly at the back half of the wooden structure behind the metal building.

I get the feeling that a reflector is not the solution for this situation, though if you have any pointers to info on them I would not mind learning more. Always good to have more info for your bag of tricks.

[admin]

Essentially you just reflect the energy in a simple line of site method. Find a location where the signal would be strong, place a metallic plate to reflect the energy where you want it to go. The larger the plate the better

[Matthew]

I kind of figured that was how a reflector would work, in this case I would need more like a pair of them, kind of like a periscope. With the antennas I think I can mount them in the center of the metal buildings A shaped roof and point one kind of sloping down the A in the house direction and the other doing the same in the other direction.

I have all the stuff to make the antennas and I find it hard to believe that I don't have at least a couple feet of twin lead kicking around someplace.

[chaicustard]

300 ohm line probably wont work well due to losses at 2.4 GHz. It doesnt like being near any other metal, and may even radiate a little
Personally, If short on antenna-making suppies , Id consider the flat-plate reflector idea.
A sturdy wood 3 or 4 ft sq frame , with well-flattened Chicken wire strung across should do the trick.
If your geometry is too 'straight' ( point of reflection makes angle of more than say, 130 degrees) you'll need 2 like a periscope.

The 2-antenna idea will work fine of course, but instead of twin-lead, Id suggest using RG-6 (75 ohm). If you do some propagation calcs, you sohuld be able to figure out how big the antenna needs to be. I would measure signal at the repeater site first. My gut tells me at least 16 -20 dBi. ( EG ; If you can get 1 microWatt at repeater, youd need a 30dBi antenna just to bring it anywhere close to a normal router) .
Once antennas get above that, their size can make them just as mechanically copmlex as a simple flat-plate.

[Airlink]

Hi Matthew,
The use of a passive WiFi repeater will work. There are a lot of online descriptions that modify a Pringle's can (or other metal can) to create a directional WiFi antenna. For instance: https://www.makeuseof.com/tag/how-to-make-a-wifi-antenna-out-of-a-pringles-can-nb/
Putting two, back-to-back would constitute a repeater. You may want to have the antenna on top of the Morton building. The antenna that is pointed at the WiFi router in your house could be more directive. I've seen some built by using a reflector from a satellite TV system, and putting a WiFi antenna in place of the horn. The other antenna may work better if it is a bit less directive (more like the Pringle's can) an can cover the area around your shop.