Why 2.4GHz? Chasing wireless history

I don't know the answer to why the 2.4GHz ISM band is at 2.4GHz, but I do know the answer as to why the 2.4GHz band was chosen over others. (I also know why the 61.5 GHZ ISM bad was chosen to be 61.5GHz.)<p>The choice of the 2.4GHz band needs to be seen in the context of 1995, when the first WLAN prototypes were built.<p>The lower limit was set by the desire to have the smallest antennas possible, to allow WLAN equipped devices to be portable. The higher the frequency, the smaller the wavelength, the smaller the antenna.<p>The upper limit was set by what was technically possible in 1995. The desire was to use cheap CMOS technology to build WLANs. In 1995, it was just possible to build a 2.4GHz radio in CMOS and research was in progress to build a 5GHz radio.<p>Consequently the first WLANs came out at 2.4GHz. Since then, WLANs have remained at that frequency for compatibility reasons (Metcalfe's law). 802.11a was defined to be 5GHz, because 802.11a came out after 802.11b and by then a 5GHz radio was possible in CMOS. Due to the dominance of 2.4GHz, 802.11g was later defined to be 802.11a at 2.4GHz, to take advantage of readily available 2.4GHz RF components, and allow 802.11a rates without having to have a dual-band radio.<p>61.5GHz was chosen for ISM because it is heavily attenuated by oxygen the atmosphere. This makes it unsuitable for long-range communications, but great for short range, since the high attenuation provides a degree of isolation between networks.

Given that the FCC is funded by the taxpayers I find it frustrating that the FCC document archive is sitting behind a paywall-esque system. Is there a good reason for this?<p>With all the money it costs to physically store and maintain the documents, I would imagine that they could instead scan and index them, and then put them up online and make them available to taxpayers for free, since we (the taxpayers) have effectively already paid for it, and continue to pay for it continually.<p>How did the BCPI become the sole contractor to have access to these documents? How can I find out how this came to be?<p><a href="http://bcpiweb.com/fcc.php" rel="nofollow">http://bcpiweb.com/fcc.php</a>:<p>&#62; Our office is inside of the FCC building and we have full complete access to FCC files,<p>&#62; FCC divisions, FCC bureaus and FCC archives! We are the official contractor given top<p>&#62; priority by the Federal Government in handling FCC documents to benefit the public.<p>&#60;sarcasm&#62;Yes, what a boon for the public.&#60;/sarcasm&#62;<p>FWIW, I hate being so negative about this. But as is often the case with governmental affairs, this seems like total bullshit.

Well, to be precise, it's 2.4GHz and 902-928MHz, so, for completeness, you'll want to chase down both of them. (I spend a <i>lot</i> of time on 902-928 MHz at 1 Watt. )

It should be somehow connected to the width of roman roads, I'm pretty sure of it. But the connection is not an obvious one: "speed of light / 2.4 gHz / (56 1/2 inch) = 0.087041".

Is it really true that microwaves would work on that whole range of frequencies? I thought there was a water resonance at 2.4 GHz that they were designed to excite.

I would say that a lot of the rationale would come from:<p>1) Availability of the 2.4GHz band in other established countries 2) Propagation characteristics of 2.4GHz (this would also explain why the 900MHz ISM band exists given the better coverage) being relatively well known at the time 3) Separation, at least originally, from heavily populated bands at the time<p>Note that the $500 funding goal would only allow for 10 hours of discovery (exc. email &#38; per-page costs), which may not be a lot if the investigator needs to find meeting minutes, memos and communications with other regulatory bodies from over half a century ago.

Good luck with your search!<p>Out of interest, have you tried approaching the University to see if they have funds available to help you out? That would be my first port of call - $500USD isn't much to them.

This wired article _seems_ to explain it:<p><a href="http://www.wired.com/gadgetlab/2010/09/wireless-explainer/2/" rel="nofollow">http://www.wired.com/gadgetlab/2010/09/wireless-explainer/2/</a>

I always assumed those were set aside as unlicensed spectrum and that was why so many things existed along those bands. Probably also some propagation characteristics?

My guess would be that it has something to do with design considerations for early cavity magnetrons, which generate the radio waves for microwave ovens.

Some speculations:<p>I suspect FCC simply allowed Raytheon to use whatever frequency its "Radarange" oven used. After all, Raytheon was the main radar producer for the US military. Presumably the military had a strong influence on FCC. Remember, it all happened in 1947, just 2 years after World War II.<p><a href="http://www.raytheon.com/ourcompany/history/leadership/" rel="nofollow">http://www.raytheon.com/ourcompany/history/leadership/</a>

I always thought it was some balance of range vs bandwidth, some nonsense about lower frequencies having larger range but having lower peak data carrying capacity, and higher bandwidths having less range but more data.<p>Which still wouldn't explain why we didn't use low bands for cellular (all the time at least, hello 900mhz) and high bands for wifi.

We had 2.4 GHz systems working in 1992. They were crude frequency hoppers, but they worked and were designed to take advantage of the FCC rules for the unlicensed ISM bands. The first WLANs that were similar to what we have today with APs and mobile clients were in the late 80s

It's crazy that everyone is using 2.4Ghz for Wi-Fi. My flat is swamped with 2.4Ghz WiFi all conflicting with each other for the 3 non-overlapping channels and the much larger 5Ghz range is completely unused.

found this article interesting: <a href="http://ca.gizmodo.com/5629814/giz-explains-why-everything-wireless-is-24ghz" rel="nofollow">http://ca.gizmodo.com/5629814/giz-explains-why-everything-wi...</a>

Ah American democracy - freedom and knowledge for all, who can afford it.

To give everyone cancer...<p>Ask yourself next time your pocket vibrates.