WiFi Locator

Direction finding requires a directional antenna. The problem is making it pocket size. At 2.4GHz, it's actually not that difficult to put a parabolic reflector behind the wi-fi detector, and spin it around looking for a peak.

I've built a few prototypes on various frequencies. For example, visualize a typical rubber ducky antenna mounted vertically. A aluminum parabolic reflector, with about the same height as the antenna, is mounted on a rotating pivot, with the rubber ducky at the center. Works well enough to determine the general direction, but is not good enough to go transmitter hunting, due to side lobes. For that, the antenna will need to be bigger. It's also rather sensitive to reflections and multipath.

I've also built doppler type direction finders, but not at 2.4GHz. Unlike my previous rants on the topic:

I think dopple has a chance of working with wi-fi because 802.11 provides an easy method of reporting signal strength from a specific radio. This is a major R&D project and not something I want to speculate upon.

So meanwhile, the best suggestion I can offer is to sacrifice a wi-fi detector, stuff it into an RF shielded box, and add an external antenna connector. Connect a directional antenna (dish, biquad, yagi, patch, whatever) to the connector, and do the transmitter hunting thing.

If you must have it pocket size, you might consider using a Windoze Mobile cell phone (with wi-fi) or suitable PDA. See:

That's what I use on my Verizon VX6700 phone/PDA/wi-fi/etc.

The Oracle has spoken..Thanks much..At eighty-five winters I have long experience with "microwave." I remember rhumbatrons, klystrons, maggies etc..I can remember when thirty mega-"cycles" was hard to get. Turn the tubes upside-down, pull off the base etc..I even remember goniometers, crystal dectors, air-cell batteries. Have sat hi-speed CW circuits using "Z" signals, i.e., ZLF ?? Have had about eight calls..Presently W6BWY..an OA, KX, etc..I admire the h... out of your background. My idea of a locator would be dual rotating antennas (phased) synced with a display of some sort..The problem with finders is that 2.4 Gigs bounces all over the place and is hard to pin down..Many years ago in countermeasures we had antennas on each side of our wings and in those days rudimentary rotating and supplying signals to amps and indicators, etc. Hawking had one detector which had some directional ability,,but nothing worth while. 73s W6BWY

I can't affort Oracle. I use MySQL instead.

Egads. That does go back. Don't forget the goniometer, gyrotron, BWO (backward wave oscillator), leecher wires, TWT (travelling wave tube), Gunn diodes oscillators, tunnel diode oscillators, 1N21 diodes, gas tube t/r switches, echo boxes, and a wide variety of antennas that defy aethetic considerations. If you know what all these are, you're either very old, very experienced, or both.

I switched from megacycles to megahertz in about 1980. However, I still use uuF instead of pF for cazapitors.

Parasitic oscillations? My favorite were acorn tubes. The would work no matter how badly I messed up the construction.

Ok, you got me on the air-cell battery. Whazzat and where's it used?

Got my novice license in about 1963 at age 14. I survived building an AC-DC 5 tube radio without getting electrocuted. Everything since then has been relatively safe and easy.

Yep. It's also a common technique used by T-hunters in various places. 73 Magazine had a series of articles in the Homing-In section on the luantic in Santa Barbara, what butchered a perfectly good Konel/Furuno marine radar, mounted it on his trash mobile, and replaced the dish with a 2 meter 5 element quad-yagi. The rotation of the antenna was synchronized with a pair of selsyns to give a circular PPI-like display. Nifty idea but more easily implimented using a shaft encoder and computah software. (Yet another project).

Yep. There are other problems. 2.4 GHz is so crowded, that it's going to be difficult seperating xmitters. The best antenna for the purpose would be a 24dBi barbeque grill dish, which has a -3dB beamwidth of about 7 degrees. That means it can resolve two xmitters seperated by more than 7 degrees. Any less, and they combine into a common blur. 360 degrees divided by 7 degrees is about 50 stations. Netstumbler now finds 20 stations here. Double that to add in the clients as Netstumbler only finds access points. So, chances are good that you'll see nothing but stations, at any compass point, and not be able to resolve or identify a single one.

Remember Dr. R.V. Jones and the Wizard War?

One of the German beam following systems he reverse engineered used a pair of moderately narrow antenna patterns, switched back and forth at a regular rate.

I think I can use the same method to obtain a rather narrow beam width for a rotating antenna RDF. (Yet another project).

Been there. I help on the AN/SRD-21 "homer". Two antennas and an RF switch. Synchronous demodulator driving a zero center meter. The Coast Guard vessel goes in circles until the meter centers. I dug the design out of an aviation electronics book from the 1930's.

It's all a matter of beam width. The narrower the better. There's nothing that can be build that's sufficiently narrow, and will also fit in your pocket.

Instead of the traditional dish, it might be possible to use a Franklin or AMOS antenna:

Lots of gain (12-18dBi), 6 degrees vertical beamwidth, 90-120 degrees horizontal beamwidth. Rotate the antenna 90 degress and spin it around. The 6 degree beamwidth should be as good as a dish and much smaller.

Thanks much...

The wifi phone works, but using body shielding is required. Mine can read out the signal strength.

Or do you have something else in mind?

Air Cells were popular in the thirties when people who could afford a radio lived out where there was no electricity. Acorn tubes?? You are a newbie...I would not use selsyns, but instead a sine/cosine array say of four verticals..I did a large amount of countermeasures around the world..Active and passive.. and really came up with one of the first ways to determine the range of an unknown signal..My favorite circuit would be a piece of galena with a needle to find a good spot, an oatmeal box with wire wrapped around it..a condenser made from Bugler tinfoil, and a borrowed telephone receiver all inside a cigar box..Later one with a transistor powered by rectified RF from the local station in town. FYI in the twenties "peanut" tubes along with O1A's existed along with type 27 detectors..etc.. I..._._

I have no mind this morning. Brain dead would be a good description.

Body blocking sorta works. I did some random testing in a parking lot, to see if I could locate a coffee shop hot spot this way. Reflections off vehicles made it all but impossible. I got my best results by walking around the perimiter of the parking lot, and simply recording the signal strength. There was a spectacular rise as I walked in front of the coffee shop, but not much else.

I also tried using a reflector behind the phone. It wasn't very high tech. Aluminium pie tin with a styrofoam spacer. That was a bit better than body blocking, but again, the reflections were fatal. The added side lobes certainly didn't help.

Unless I missed something in the technique, methinks a directional antenna is the only way to do direction finding.

What type of anode? zinc? aluminum? etc? I thought zinc-air batteries were only good for low power applications like hearing aids.

I'm only 60.7 years old and still working to support the medical and government sector. I learned much of my electronics on the junk left over from WWII.

Adcock array? Watson-Watt antenna? That requires either two matched receivers or really good phase matched antennas, coax, and RF switch. Add a 3rd receiver for a "sense" antenna, to get rid of the 180 degree ambiguity. I've worked with some of the OAR (now part of Cubic Comm) HF RDF stuff. Works so-so on HF and VHF. Not recommended, useful, or cost effective for microwave.

Nice. I did some experimenting with internet connected receivers and GPS time sync. I compare the time of arrival at various receivers around the world. Try to guess if it's ground wave, sky wave, and how many bounces. Triangulate using the path lengths. It works fairly well and is able to locate HF stations to within about a 5 mile radius. I've also played with wave front direction finders and interferometery techniques.

I've also done some crude direction finding on VHF/UHF through a repeater. I would time the audio delay through the repeater and compare the delays between a receiver on the repeater input, and a receiver on the repeater output. The constant difference lines form a hyperbola. Standard Loran style hyperbolic navigation can be used to get a line of position. If I know which freeway the mobile is driving, I can

I never could get my (lead) crystal set to work in skool. My first working AM radio used an extremely expensive 2N370(?) transistor. I blew up a succession of CK-722 transistors trying to make a radio that worked. Not bad for a 12 year old.

Too ancient for me. I still have a small collection of early tube type walkie talkies and some early cell phones. I'll post some photos on my web pile when I have time. Someone is giving a presentation to our radio club on Friday on the original BC-222 WWII HF walkie-talkie. I used to scrap those for parts because they were nearly useless for tx power and rx sensitivity.

I for one would like to know where the antennas are located in my cell phone (wifi and cellular). The same goes for my "SPOT". I assume the cell phone is designed for the handset to be held vertically.

Any particular model cell phone?

Remove battery from cell phone. Look at serial number tag. It will have the FCC ID. Go unto the FCC ID web site and look at the inside photos. There are also web sites that specialize in disassembly and repair instructions.

What's a "spot"?

Yeah, I forgot about the FCC website.

Regarding SPOT:

'm not much for being an early adopter, but I got this when it was new on the market. Thus far it has worked in every hell hole I explored.

I did the hike to Berry Creek Falls years ago. It was the only place I ever visited where the GPS just plain failed to work. I suspect the spot would have trouble there too. Then again, I now have a GPS60, while back then I was using the eMap.

The majority of my background is airborne. That pretty well limits what can be used. The system which proved effective for me involved the use of computers in light of changing headings, altitudes, velocities etc..And this was in the fifties and sixties when we were not far along..BCNU