Amateur Radio Packet Over 802.11 Cards

Skuld-Chan writes: "I stumbled across this the other day -- basically discusses modifying common 802.11 boards for amateur radio bands (or Part 97 rules). Under Part 97 there is a 100 watt limit and no gain limit (unlike the 6 db gain limit on Part 15). I thought it was interesting :)." Consult your friendly branch of the FCC :) Note that this is just one of several interesting projects from this site.

Comments

interference

[CmdrTaco (editor)]

What kind of interference will this cause? If everyone with with 802.11 capabilities starts broadcasting, will it cause any problems? I've heard bluetooth and things like microwaves and 2.4 GHz cordless phones don't get along so well with this technology.

Re:interference

[AndroidCat]

Once you get up to those power levels, you could try Moon-bounce relaying. Of course, you need one heck of an antenna! (This isn't Buck Rogers, some Hams do this sort of thing.)

I suspect the bps would be fairly low, but I haven't checked on the state of the art in a couple decades. Oh yeah, add 1.5 seconds to the packet latency! :^)

ping moon ...

Re:interference

[Perdo]

A microwave oven has a "white" high power amplifier inside. It tries to transmit as close to 2.4 Ghz as possible, as this is the resonate frequency of water molecules. The actuality is they produce a more "white" RF, like a white lightbulb produces a broad spectrum of light compared to a laser. Any saw filter placed on such a transmitter, would get very hot indeed, and would waste the energy that could be used to heat the food. The filter would get hot instead of the food.

Since the RF is white, there is no way to design a feedhorn or antenna to properly radiate the power. High VSWR would kill the transmitter in a very short period of time. Food in the microwave acts like a dummy load. It absorbs the RF, so little gets reflected back into the transmitter. VSWR as low as 15% of total power out of a klystron will make it explode in just a few seconds. The electrons "piling up" forces the klystron to act like a capacitor, and the electron gun will arc with the collector, causing the glass vacume chamber surrounded by rare earth magnets to implode with a force compounded by the high voltage being applied to it.

Suffice to say, a klystron out of tune or improperly capacitance match with it's antenna goes like a grenade.

Make sure you disable the power supply safety interlocks and bypass the fuses in addition to cutting a hole in the door of the microwave to achieve this effect.

Re:interference

[fatboy]

What kind of interference will this cause? If everyone with with 802.11 capabilities starts broadcasting, will it cause any problems? I've heard bluetooth and things like microwaves and 2.4 GHz cordless phones don't get along so well with this technology.

As a "Joe User" with an off the shelf, Part 15 device, you must accept any interference that comes your way. You must also not cause any interference. You are an unlicensed user of the spectrum.

As a ham on the other hand, you can modify the part 15 Device to your allocated freqs, amplify the power output and modify the antenna system. You will also have priority over the Part 15 Devices that coexist in your spectrum.

DE KE4PJW

Re:interference

[stevew]

It's not a myth!

For line-of-site, beamed, i.e. direct communications in particular. Anyone who has done 2m Transmitter hunts can tell you it's real. For that matter, try doing 2m side-band and you'll find that the average user is horizontally polarized compared to the FM croud which use vertical. Again, an easily observed difference. You put up two antennas and flip a switch, you'll see a difference in signal level.

Now - a few of things about doing this in the US. The first issue is content rules. No bad words, etc over the ham frequencies. So that let's you off going to that favorite porn site of yours. You can forget a usenet feed. Hams are actually limited as to what the what they can say over the radio, same is going to be true of digital communications.

Another is no encryption. No need to worry about whether you need 40 bit or 128. Can use either in the ham bands.

What about monitoring what comes through your digital repeater station. You DO know you're responsible for it don't you?

It's an interesting experiment idea, and I can think of some neat OTHER applications beyond the internet. Hams are into talking. Maybe this is a relatively cheap Digitial repeater system and you move Voice data over it in a wide area network using dishes?

100 Watt wireless router?

[Karl Cocknozzle]

My wireless router is at about eye level, about a foot away, on a shelf here in my office. If that sucker was putting out 100 watts I probably wouldn't have it so close to my head anymore...

Re:100 Watt wireless router?

[Perdo]

RF poisoning symptom progression:

Head ache.
Stomach ache.
Permanent Sterility.
Unconsciousness.
Death.

In other word, if the RF makes you pass out, welcome to silicone testicles and Testosterone shots for the rest of your life.

Re:100 Watt wireless router?

[Perdo]

I was witness to a darwin award winner who unlatched a waveguide and looked into the rectangle end. He said "hey, there's hot air blowing out of here". I looked at him to see what he was talking about, then destroyed two klystrons by slapping the main power breaker. Klystrons need cooling air to prevent them from cracking and implodeing after the driving voltage is removed from them.

This warm air is also bled into the waveguide itself to drive out any moisture that would impede your signal.

You see, the guy looked straight into a waveguide pumping out 2000 watts at 4.7 Ghz that required 30,000 watts of 480 volt 3 phase AC to generate.

And that dude, well, that dude was dead before he finished the word "here"

AN/TRC-170 V2 Army/Airforce Mobile Troposcatter. Baddest pair of micky mouse ears you will ever see on a battle field. Two 81 db gain 10 foot dishes, 10 feet in the air, and 10 feet apart. 560 foot danger zone in front of the dishes. After a few days transmitting, the ground in front of the dishes would be littered with the corpses of birds, rodents and the scavengers that came for the easy meals.

Long distances...

[geogeek6_7]

Now instead of being like "Wow! This station is 1,200 miles away!" We can be like "Wow! The interference thats making this packetloss is coming from 1,200 miles away!"

Before everyone jumps on the bandwagon...

[Jay Maynard]

...it's worth a reminder that amateur packet radio is subject to a number of content restrictions that make it extremely poorly suited as a transport medium for general Internet traffic. It's only useful for sending stuff from one ham to another.

That said, I may do some hacking in this area myself...

...de K5ZC

Re:Before everyone jumps on the bandwagon...

[Bishop]

There are two important restrictions that should be concidered. In North America you may not transmit in code. i.e you can't use crypto. The second restriction is a tough judgement call: you can't use the amature bands for commercial use. This may restrict you from shopping on line over an amature band WAN.

There are some other restrictions, but these are probably the two big ones that will affect the /. crowd.

Re:Before everyone jumps on the bandwagon...

[Sc00ter]

Actually.. shopping is a little iffy.. For example, you can't use autopatch (using your handheld radio to patch into a phone like via a repeater) to call a business client, but you can use it to order a pizza on your way home.

A couple of things apply here...

[bovinewasteproduct]

First off you must be ham radio operator. Since these all operate above 50Mhz, this means you can get by with a Tech license which is no code, just study and pass the written test. Sites to check for ham radio licensing info include E-Ham and the ARRL.

Second, any system with more that 1 watt output must be under automatic control so that only enough power as required to compleate the communication is used. You just can't pump out 100 watts to go next door. Not that 100 watts at 2.4Ghz is easy to come by...

The nice thing is that is looks like you don't even have to touch some of the boards to do this. Talk to the manufacture, show them your license and they'll set you up with boards in the ham bands right off the bat! Nice!

BWP

Would https be a violation?

[iamroot]

The FCC laws state that you may not use ciphers to obscure the meaning of your transmissions. What if someone was using https, ssh, or another encrypted protocol over this? Would that be a violation? Its not really clear what that part of the amateur radio laws mean. If that would be a violation, then I'd have to wonder about the practicality of this. Aside from an alternative to TNCs, there might be problems with actually setting up a network, aside from the fact that anyone on it would need licenses.

Licence revoked:

[Perdo]

Transmit 100 watts across a city, at 2.4 Ghz, and see how long before your amateur radio license is revoked. Part of their rules are to never use more power to conduct your transmission than is necessary. Since 100mw with a high gain antenna is enough power to transmit to the limits of practical line of sight, using more than 100mw is using more power than is necessary. Also, to transmit, you must listen to the channel you are about to transmit on to insure no one else is using that frequency at that moment. Since 2.4 Ghz devices have become so ubiquitous, it is impossible to transmit without stepping on someone, somewhere.

This story reminds me of the one about the website that teaches people to make an x-ray machine. Nice to know, but definitely not for the irresponsible masses.

Re:Licence revoked:

[Perdo]

The automatic gain control on the low noise amplifier in the receive section of the card would shut down the receive path for any card inside the structure where the 100 watt omni is located. Think of when you yell into a mike and it cuts out to protect itself. So, you could provide strong signal to everyone, unless they were too close to you.

And as the article mentioned, this applies to Packet Radio, which by it's nature has a single source and a single destination. Omni directional antennas are used primarily for point to multipoint communication not point to point as is typically used for packet radio.

Also, remember the inverse square law when designing your network. Putting more power into your transmitter does less to improve communications performance at a distance than a properly designed antenna. High gain omni directional antennas are more efficient at propagating your signal than increasing your power to 100w.

For instance, a 15 dBi High Performance Omni sold here for $209.95 increases the effective radiated power by a factor of 100,000. A factor of 10 for every 3 db of gain. So, your standard 100mw transmitter would transmit less power than the 100w transmitter initially, but would fall off less with distance, surpassing the performance of a 100w transmitter on a standard antenna after the first few feet.

The other route is to use a 2.4 Ghz Klystron like this that costs in the neighborhood of $30,000 which of course can be coupled with an high gain antenna, which will not survive long at its maximum rated load.

This is not a competition of Penis sizes or "My athlon is faster than your Intel boxen" this is a game of finesse where the sharpest mind and the most efficient system dominates through signal quality, not signal quantity.

You get Mary on her 2.4 phone and the Muni Hospital complaining about you ruining ther gossip chat and emergency beeper service and you won't just loose you expensive 'leet 2.4 Ghz gear, you will do prison time for willfully jamming vital communications services, tantamount to a terrorist act, post 911.

Want to be 'leet? Implement a flat panel phased array with electronic beam steering to pinpoint your distant end receiver at gain levels limited only by the precision of the real time clock you use to gate the injection of the 0-180 and 180-360 phases of your waveform.

That would cover as many stations as you wanted, within the limits of line of sight. You could go back to college to learn the RF theory necessary to build such a device for the price of a big dumb klystron and go on to dominate the mobile gigabit bandwidth telecommunications arena. Perhaps your choice is clear.

'cept you have to compete with me, and I'm 11 years ahead of you :)

W-ERZ

[Renraku]

Thank you for listening to W-ERZ. We're taking requests.."Hi..what would you like today?" "I'd like a copy of Windows XP." "You use that garbage? Alright, coming right up. Thanks for calling! You're listening to W-ERZ, all warez, all the time."

Re:If I had speakers that handled it..

[Chanc_Gorkon]

Music and amatuer radio doesn't mix (not sure if the data would be though like if it would be a MP3....). The only station allowed to broadcast music on the amatuer bands is the space shuttle.

moon bounce

[trex44]

Back in the early 80s, HAM enthusiasts used to do moon bouncing using VHF (144Mhz band) 100w radios feeding highly directional helical antennas pointed directly at the moon. The idea is to use the moon as a passive satellite to bounce the signal back to earth. Back then, 300bps packet radio communication was attainable using this technique. I wonder what kind of interference levels can be expected if some HAM operator did this on 2.4Ghz today? Would the bounced signal be strong enough to cause real interference across a large portion of the globe?

-.. . DU1DQ

Re:I'd recommend against it!

[OverCode@work]

One of the privileges of an amateur radio license is modifying radio equipment with the intent of operating it on amateur frequency ranges. This is why amateur radio requires a license -- if you don't know what you're doing, you can cause serious problems. The FCC places a lot of trust in ham operators by essentially giving them a blank check for experimentation.

So yes, hams are allowed to hack wireless cards to work on their frequencies. They're expected to know what frequencies they may use, how much power they're putting out, how to resolve any resulting interference, and so forth.

BTW, it is not very difficult to get a ham license. Contact your local radio club, or have a look at http://www.arrl.org. Just takes a bit of reading, $10, and a 35-question multiple choice exam.

-John, KG4RUO