Amateur Radio Operators License = More Power? 125 Mile WiFi
Last Post: November 8, 2005:
For those of you that don't know, the current world record for a point to point Wi-Fi link is 125 miles. They say that they did this un-amplified, but they use a 300mw card. The antennas they used were old 10 and 12 foot satellite dishes. I commend the effort and engineering they did, but I think that they were exceeding FCC limits.
On their site, they state that since they are amateur radio operators they can operate at a higher power level. Is this correct? It?¡é?€??s tough for me to believe because then any company that wanted to exceed FCC limits would just have an employee pass the test.
Even using the 3:1 rules for a point to point link, there is no way that 300mw into an estimated 50dBi (complete guess) antenna is within the limits. Even with 10dB loss for cable and connectors (no way that high) the output power would be an astronomical 3000 Watts!
I'm not trying to debunk their achievement, but I would like some confirmation/denial for some of my questions. Thanks a lot for your time!
As a ham, I have to admit I was really stumped on this one. Thanks to google for the answer. Your specific answer is in the 5th question of this document: http://www.qrpis.org/~k3ng/ham_wisp.html This guy really put together a great FAQ on the subject, and WISP's in general.
You know, I always called my old X band radar detector a "10 Ghz mobile CW beacon transmitter receiver". It really is.
Lets call CQ!
Thank you for the quick reply. I have many questions... My first thought was for me to get my ham license so I can use a higher power at a WISP. It says that amatuer radio freqs can't be used for profit. But, the 2.4Ghz ISM band wouldn't be amatuer radio band, it would be an unlicensed band right? So, if I owned a WISP, which clause would I fall under if I was a ham? You may not know the answer, but these are just questions going through my head.
The FAQ's state that you cannot have a transmitter over 100W. Is the radio considered the transmitter or is it the intentional radiator, or EIRP at the antenna?
Then, it says that it can have no more than 23dB at the intended receiver. Of course that is more than plenty for communications with 802.11.
Thanks again for the information, but now I'm more curious than every.
Oh... to fall under these rules, does a ham have to be at the transmitter site or do they just have to maintain it, or did they just have to design it? :)
... It says that amatuer radio freqs can't be used for profit ...
I know there are differences between the US and the Australian (where I am) amateur regulations but as the holder of an advanced class amateur licence for several decades I can probably answer this with some authority.
The key point here is that it isn't the frequencies which are licenced. The rule is that under the terms of an amateur radio licence you cannot operate any equipment for any commercial purpose. This is a fundemental principle of the amateur radio service throughout the World.
There are dozens of other regulations pertaining to the amateur service which preclude running high powered 802.11b. For example, when operating under an amateur licence, licencees can generally only communicate with other licenced amateurs ... so as a WISP, all your customers would also need to be licenced amateur operators.
Basically, if you were to attempt to use an amatuer licence to run high power as a commercial WISP you would have the FCC jumping on you from a great height very quickly!. Even using high power for non-commercial purposes could land you in hot water if you were communicating with non-amateurs.
Having said that, an amateur radio licence is a distinct bonus in our field of endeavour. Most licenced radio amateurs with a few years experience under their belt would breeze through the RF topics of CWNA.
Thanks a lot for that information. It really helps a lot to know the purpose of a regulation instead of just the raw text.
With the being said, there should be a shoot out to see how far 802.11 can go without exceeding FCC limits and without holding an ham radio license. Again, I'm not trying to diminish what the guys did at DEFCON, but it would be great to know what regular guys could do and still stay within the regulations.
Yes, I agree. That would be an interesting thing to do. Some amazing distances could possibly be achieved using things like ducting on over water paths.
Since first being achieved by radio amateurs in 1970, numerous amateurs around the World have made successful two-way contact at 2.4GHz by bouncing signals off the moon! ... but of course at very narrow bandwidths and very high power. Imagine the path loss for the round trip of around half a million miles!. It's a lot more difficult these days as a result of the spectrum pollution from microwave ovens and the ubiquitous 2.4GHz "wireless everything" ... from phones to 802.11b.
If anyone wants to do the math, assume a path loss of around 270dB and a receiver sensitivity of -90dBm for the 802.11b receiver. I'm thinking transmitter and receiver antennae along the lines of Arecibo! :)
As far as 802.11b is concerned there should be some ground rules ... configured within the regulations and exchange a given amount of data in both directions for a distance record to be considered valid.
The record you quoted earlier is not really valid in my opinion. As you correctly point out, the EIRP resulting from the large dishes vastly exceeds what is allowed under the regulations.
Ultimately I suspect that 802.11b would fail as a result of timing issues rather than signal propagation. Some more trivia ... it would take around 2.5 seconds for your radio signal (at the speed of light) to make the round trip to the moon and back!
Bouncing 802.11 off of the moon.. now that is cool. It may work at the MAC layer as long as you set your ACK timeout to over 2.5 seconds. :) That would be a very long ping reply.
I think we should come up with some ground rules for sure. We should hold a CWNP contest... Devin.. are you listening? :)
My longest 802.11b 2.4GHz link here is around 25 miles ... but we are limited to 4 Watts EIRP in this country.