Parabolic dish with usb wireless

Fiddling is done with a fiddle or violin. What manner of butchery were you trying to avoid? As for getting ripped off, wanna try to build your own from parts? You won't like the connector prices.

The basic problem with shoving a USB dongle at the focus of a dish or corner reflector is illumination efficiency. Maybe an optical analogy is easier to understand. The USB dongle does a fair job of radiating equally in all directions, very much like a light bulb. I you put a reflector behind the light bulb, you'll have some of the light emitted by the light bulb reflected from the reflector, but the greatest majority of the bulbs light will end up going in directions where you don't want it to go. This is called "overspray". The same thing happens to 2.4Ghz wireless. Much of the signal is lost and not reflected. Oh yeah, just to make life interesting, the best efficiency a mesh or solid reflector can do is about 50% (losing -3dB gain). Obviously, a reflector will improve the gain of the insipid tiny PIFA antennas used in most USB dongles. Anything is an improvement. However, don't expect spectacular gain and you will see LOTS of side lobes.

See:

Personally, methinks the way to go with USB is removing the PIFA antenna and replacing it with an SMA connector. The connector would then go to a proper panel, patch, biquad, or dish antenna. At least all the RF goes to where it's suppose to end up.

emitted

So you mean that it is okay for focusing the signals that its receiving BUT the improvement in transmission is not that much. And what's the point of receiving a wireless signal if you can't send back a reply from a distance (unless you just want to use it to capture packets). Therefore you need a parabolic dish at both ends to pick up each others weak and misdirected signals. Am i right in interpretation of what you said?

My initial thoughts was that it would be not much better at sending a signal but i thought that i was wrong. Based on my knowledge of constructing solar concentrators/furnaces.

How is it good for wardriving? (Not that this is what i want it for but another guy mentioned this) You would only be seeing an increase in reception ability and not transmission strenght therefore what's the point if you can see all these networks but can't talk to them any better.

Slowly i'm piecing together the general workings of the field at practical level.

BTW, i can get one rp-sma + one n type connector for around $6-7.00 which is what you need for a lot of cards (eg. netgear) therefore building a pigtail isn't that expensive BUT you probably need a crimper for the rp-sma.. or do you?

Thanks, Stephen

I made a parabolic reflector for war driving using the below pdf template, and use it with a Microsoft USB wireless adapter that has a flip up antenna. Works pretty good and has noticable gain using the netstumbler signal strength display. Noticable improvement connecting to distant spots. Made it with a piece of thin cardboard to hold the parabolic shape, a piece of manilla folder with aluminum foil attached for the reflector, hot glue, and a hole in the cardboard to slip over the antenna at the appropriate point. It all depends on what your needs are (business vs. hobby) and how much $$$ you want to spend.

Not exactly. Let's go back to my light analogy. If you're receiving light from a distant source, all the light that bounces off the reflector is reflected back to the detector at the focus. This is good. However, if you're transmitting light, from a non-optimum illuminating source such as an ordinary light bulb, much of the "transmitted" light will end up going everywhere except to the reflector. If half the light goes off in some direction other than the reflector, you lose 3dB. My guess(tm), assuming a spherical radiation pattern, and a typical 0.5 f/D ratio barbeque grill dish, only about 1/8th of the signal (light) makes it to the dish for a loss of 9dB. Yes, this means that the "gain" of such an antenna is different in transmit and receive. You don't see different tx/rx specifications for commerical dish antennas because they have properly designed feeds, where most of the TX signal hits the dish (and uses the full surface area of the dish). In such cases, the difference between tx and rx gain is negligible.

Read the part on reflector illumination and spillover:

Dunno. Any kind of reflector, that redirects signal in the desired direction, is a good thing (as long as it doesn't cancel or interfere with the direct signal).

True. Note that the DWL-122 antenna is backed by a ground plane (the main circuit board) and therefore has less radiation in that direction:

Yep. Don't be suprised if the received signal, when compared to the internal antenna or rubber ducky antenna, increases different amounts at each end of the link, with a reflected antenna using an inefficient feed.

I hear expresso and caffinated has more "punch" than decaf, which is rather inspid.

The reflector works in both transmit and receive.

There will be noise received from the "back" side of the USB dongle as well as from the reflector side. Some other radiator would make more effective use of the reflector. That's not to say that the reflector doesn't help. The New Zealand site has some annectdotal data that says that a reflector improves the connection. I don't find the USB dongle to be very omni. I think it is heavily loaded toward the label side of the DLink-DWL-122. That would make the reflector more helpful than if it were a good omni.

To your other question, Netstumbler only shows receive signal and noise. Some client programs provided with WiFi clients show "this signal" and "partner signal". That would be a better evaluator of the dish.

I haven't used a reflector, but I have used a coffee can for a USB dongle.