I occasionally look at my referers to see what people are searching for when they find my blog. There were two in the recent list that stuck out to me: "convert dB to gain" and "chicago route around no tolls". I've obviously touched on these before, or else people wouldn't be finding my blog so easily, but I haven't talked about either directly, so here we go.

Decibels are a dimensionless unit used to relate a measured level against a reference standard. The actual unit is the "bel"; one bel represents a tenfold increase in level as compared to the standard. A decibel is a tenth of a bel, and therefore represents an increase of about 25%, since 10^0.1 is approximately 1.25. To convert decibels to an absolute gain figure, one simply raises ten to the power of the gain ratio expressed in bels. If G is the gain in decibels, then g=10^G/10 is the absolute gain multiplier. The reverse is done with logarithms and is left (for now) as an exercise for the reader.

As for finding a route around Chicago that avoids tolls, this is more complicated. In part, it depends on where you're trying to get and from where. The most common situation where this comes up is when someone is going east to west (or west to east) on I-90 and is routed through Chicago. (I-80 doesn't actually go into Chicago.) Interstate 90 is toll from the Wisconsin state line to just outside Chicago, and then again on the south side of Chicago; avoiding it is not easy. In addition, using the freeway part of I-90 to go through Chicago is not terribly fun; the Dan Ryan is widely regarded as one of the least pleasant freeways on which to drive.

Avoiding the the Skyway toll is easy; just enter Illinois on I-80/94 instead of on I-90. If you're already avoiding tolls you've done this anyway since I-90 in Indiana is the western end of the Indiana Toll Road. Avoiding the Jane Addams toll is much harder as there are no suitable alternative routes for most of its length. (You can avoid the east terminus toll by using I-290.) A lower-toll alternative is I-80 and I-39; you only pay one toll on the portion of I-80 that is overlaid on the Tristate and one on the portion of I-39 that is overlaid on the Jane Addams. You could avoid these by using lesser surface routes, but none of these alternates is very enjoyable. If you're heading far enough west, consider taking I-80 all the way to I-35 (in Iowa) to reconnect with I-90 in Minnesota. If you're coming up from central Indiana, consider using I-74 to I-39 (in Bloomington) or I-80 (in the general area of the Quad Cities). If you are heading up into the Wisconsin coast (Kenosha or Milwaukee), you can try using US 41 instead of I-94 from the north side of Chicago.

Hope this helps someone. If not, oh well.

I'm very much aware of all the furor, and do not wish to add to it further. It seems, however, that negative public opinion of "one of the most prolific reputation and defamation engines on the internet" is spreading fast:



(Taken from the May 10, 2008 issue of Secret Asian Man by Tak Toyoshima at comics.com; link will only be good for two weeks, sorry.)

A recent commentator in my blog remarked that there has been a declining interest in amateur radio, citing as a reason for this an increase in the availability of computers and the Internet.

While I think wider availability of the Internet may be a factor, I don't think it's a major one. The Internet is not really a substitute for amateur radio. While both do permit relatively inexpensive long-range communications, the nature of those communications are quite different. Amateur radio permits mostly immediate, relatively low bandwidth, personal contacts between people who would otherwise likely never meet. While there are those in amateur radio who pursue packet radio and other store-and-forward technologies, even in their heyday these were not a major aspect of the hobby for most people involved. (In part, this is due to the regulations that strictly limit third-party traffic on ham radio frequencies, which has amongst their effect making it impossible to use ham radio to connect directly to the Internet.) The main appeal to most people in the avocation has always been talking to other people at a long distance, from wherever they might happen to be.

No, it's not the Internet that is killing ham radio. If anything, the Internet is helping it. What is killing ham radio, at least in the West, is the cellphone. Prior to the cellphone, there were very few options for people who wanted reliable mobile communications. There was, of course, CB, but it's only good for a few miles if you follow the rules (which most of the people using it don't, sadly) and only a few more miles after that even if you don't. And CB is also full of obnoxious loudmouths who seem to exist only to hear themselves talk (they're not interested in having an actual conversation), making it nearly useless as a personal communication service anyway. You could, of course, obtain a business class license and use "color-dot" radios, but those licenses are not particularly cheap and the radios (at least back before 1990) also not all that cheap. Practical for a business; not practical for people who just want to be able to talk to one another when they're out and about.

There was one final option: you could get an amateur radio license and use VHF or UHF handhelds. Relatively affordable and reasonably sized two-meter (144-148 MHz) handhelds were available for the amateur service long before cellphones were widely available to the public. In simplex mode a two-meter HT (handheld transceiver) has a modest but decent range; used in conjunction with a well-located amateur repeater station a group of hams with two-meter HTs could easily maintain contact with one another over the area of a mid-sized city. The introduction of the "no-code Tech" license in the United States in 1991 helped here; this license gave broad privileges on VHF and higher frequencies without requiring the licensee to learn Morse code and made it much easier to attract technically competent people to the hobby who didn't want to take the time to learn Morse (a technology which computers have largely made obsolete). This did lead to a surge in licensing, but many of those who got their licenses in 1991 have since drifted away.

Enter cell phones. While the idea of cellular radio was invented in 1947, and the cell phone itself in 1973, the early models were large, expensive, and had very limited service areas. (Even as late as 1995 a cell phone was substantially more expensive than a 2m HT, and the HT has no "service contract" that has to be paid monthly; even if you used a repeater and the repeater operator asked that you join the club and pay dues, the dues were probably less than what you'd pay for a cell phone contract.) It wasn't until the late 90s that cellphones became widespread, and not until the early 2000s before they became ubiquitous. Now, for a relatively small fee, can get the same thing using a cellphone, and on top of that call anyone else they might care to talk to as well. Given a choice between a VHF HT or a cellphone, the cellphone wins nearly hands-down for this sort of communication in almost all situations now.

That's not to say that there's nothing interesting going on in the amateur radio world; it's not just a bunch of nerds in their garages beeping at one another in Morse code (although, to be fair, there still is some of that going on).

One big thing right now in radio seems to be software-defined radios (SDRs), and this is an area where free software can and should be getting involved. Traditional radios have used discrete, specialized circuits designed specifically for the application at hand, which means a given radio is good for, say 2m FM reception but not much use for anything else. "All mode" radios can receive and transmit multiple modulations, but they do this typically by having physical (or electronic) switches that gate the signal to the appropriate modulators and product detectors, which introduces the possibility of loss and makes the radio much more complicated (and therefore expensive). SDRs are different.

In its ultimate form, an SDR is a analog-to-digital converter (ADC) attached directly to an antenna. As there are few ADCs that can process signals at the frequencies used for many forms of radio (the current limit is around 40 megahertz), and there are other practical limitations, what is done instead is a traditional front-end is used to select a portion of the radio spectrum to receive, which is then preconditioned using (typically) a superheterodyne mixer to produce an intermediate frequency signal suitable to be shoved into the ADC. Everything else is done by the ADC. Transmitting works the same way, in reverse; a digital-to-analog converter (DAC) generates an IF signal that is then either merely amplified and put directly on the antenna (for sufficiently low frequencies) or fed into appropriate mixers or transverters for VHF and up. Since all the digital signal processing is done by the computer, the radio can have all of its functionality, other than its fundamental RF receive and transmit frequency capabilities, reprogrammed merely be changing the software load. Since virtually all computers out there today have ADCs and DACs in them, in the form of a sound card, this is something that most anyone with a computer can do with minimal investment. For somewhat more investment, there are hardware solutions (such as the Universal Software Radio Peripheral) that offer more capability by providing more powerful ADCs and DACs than are found in your average sound card, along with a FPGA solution to allow for faster processing. And, of course, the opportunity for homebrew solutions is huge here, too.

There is already an open-source project working in this area: GNU Radio. One of the reason it's important for open-source advocates to get involved in this now is that SDRs are quite likely the direction the radio industry is going. And, of course, the solutions being created by the commercial manufacturers are locked-up-tight proprietary you-can't-touch-this approaches that limit freedom just as much as any other proprietary solution. We need for there to be open alternatives so that people will be inclined to adopt open approaches that let us use the hardware we pay for the way we want to. There are some freakingly neat things being done by the GNU Radio people.

There's also some very fascinating work in weak signal developing codes and methods that can punch a message through noise, which should appeal to those with interests in compression, information theory, and data reconstruction. Morse is surprisingly good for this purpose, but there are better codes out there. The computer has really revolutionized this area of the hobby as well (although not without some controversy).

I haven't mentioned Echolink or IRLP, either; both of these are fusions between ham radio and the Internet.

In any case, I don't think computers and the Internet are killing ham radio. The cellphone, while it certainly has had an impact, is not the real problem, either. I think the real problem is much more complicated and has to do with attitudes toward engineering and science in Western society more than anything else. Ham radio is very much alive in Japan and in much of the developing world, after all.

And we definitely need more hams; with our increasing dependence on telecommunications for everything we do, we need to have ham radio operators equipped, trained, and ready for when disaster strikes and the grid falls down. (Which is also why we really do need to keep Morse: it's just about the best way to punch a message through noise that doesn't require complicated equipment, just a trained operator and something that you can pulse on and off. All these other fancy digital modes are basically useless without a computer.) It's for this reason as much as anything else that I carry my HT with me most of the time.

The FCC last year removed all Morse code requirements (as have most other countries) for amateur radio licensing, and this appears to have caused another upsurge in interest. It'll be interesting to see how long it lasts.

Last week the FCC denied a STA (Special Temporary Authorization) requested by Miller Motorsports in Tooele, Utah that would, had it been granted, allowed Miller to, inter alia, temporarily use a part of the 70 centimeter band allocated (on a secondary basis) to the amateur radio service for coordination of various services related to the scheduled holding of the HANNspree Superbike World Championship at the end of May, 2008. The FCC's denial seems to have been predicated on the idea that the proposed use of the amateur radio frequencies would unduly burden amateur radio operators, even though many other races have been granted STAs under similar circumstances in the past.

In this case, though, I think the denial is based not so much on the particulars of this request (which, from what I've been able to piece together, aren't that unusual for a racing event), but rather on whose behalf the request is made. Bikers, and especially offroad, rough-terrain bikers, apparently routinely use radios certificated only for use in the amateur radio service for personal communications without bothering with obtaining amateur radio operator licenses. See, for example, this thread on a biker's board, in which the lead poster raves about the merits of the Yaesu FTM-10R for use on his motorbike. This radio is a Part 97 certificated radio and requires an amateur radio license to use. Using it without a license is simply illegal. However, when someone came along and mentioned this, another poster basically announced contempt for the existing regulations and the original poster told the poster pointing out the illegality that they weren't interested in hearing about it.

In fact, I suspect the reason Miller wanted to use the ham frequencies is because most of the racers and crews in the planned race already have ham radios and so this precludes them having to go out and buy another radio. Ham radios are the only commercially-available radios in the United States that are "frequency-agile" (all other services are channelized), and most have trivial mods to allow out-of-band transmit, making them especially appealing to people who don't plan to follow the FCC's rules.

I find it unlikely that the attitudes expressed by those two posters are extraordinary in the motorbiking community. While I haven't read the FCC's decision (I haven't found a source for it yet), I wouldn't be surprised if their decision to deny Miller Motorsports' request for a biking event wasn't at least somewhat motivated by an awareness of a widespread streak of contempt for the FCC's jurisdiction and authority over wireless communications. If there's one thing that's bound to get the FCC to really go hard on your ass, it's demonstrating a lack of respect for the FCC's authority.

I'd really like to see what the full FCC decision is. I haven't found it anywhere on the FCC's site, but there's lots of nooks and crannies there and I could easily have missed it.

Update: I found Miller Motorsports filing for the STA in ULS, as well as their current license for a 450 MHz business pool service with 2 bases and 100 mobiles, and their other current license for 450 MHz business pool service with 5 bases and 70 mobiles, both in the same location. Unfortunately, ULS does not have the "offline" STA decision letter or the ARRL's informal objection.

It is getting warmer here, and it will soon be time to rig up the air conditioners for the house. Our house has radiant hot water heat, for which I am eternally grateful in the winter (not only does it cost less, but there's no roaring fan stirring up dust), but which means we do not have central air conditioning, and have to rely on spot coolers instead. To serve this need, we have a larger window unit that goes in the kitchen window, a smaller one that goes in the upstairs bedroom window, and a small "office air conditioner" that goes in the family room. This latter unit is a pedestal model with air hoses that go to the outside for heat exchanger air. Last year, we put this on a small table and ran the hoses out the window, stuffing the gaps with towels. (I meant to cut a panel for the hoses, but when I went to do so, my table saw shot me in the belly, a wound which took some time to recover from and which deepsixed that project for the season.) The table we used last year had the shortcoming that it was too low to allow the condensate tank to gravity-drain out the window (we had to drain it manually into a bucket every day or so). And we're currently using that table for something else now, anyway. So making a custom table for the air conditioner to sit on seemed in order.

I rooted around in the garage (which I had spent most of yesterday cleaning; we can now go in and out both doors with relative ease) and found a sheet of 4/4 melamine that was about the right size for the A/C to sit on. Some in-situ experimentation suggested that the best approach was to rest one end of the sheet on the windowsill, and mount legs on the other end. We added to this sides that would help keep the A/C from rolling off the table. These were cut down from some scrap 12 inch wide 4/4 pine stock that we bought from a cutoffs bin at Menard's a while ago, with a dado to receive the melamine cut on the back faces. This all went together reasonably easily, but the assembly lacked stiffness. This is where the sliding dovetails come in.

Using a router table, I cut stopped dovetail dadoes in the sides, near the front and the back. I then cut a dovetail into the ends of another piece of 4/4 pine stock that was laying about in the garage (we really do have a lot of scrap wood laying about), and then ripped that piece in half on the table saw, thereby guaranteeing that the two braces are exactly the same length. These slid beautifully into the sides of the table, creating a very stable and rigid frame. The front piece will be glued on (it friction-fits well enough on the front of the melamine top, but glue will keep it from falling off entirely), and the top slides into the dadoes cut on the sides and front without any fastening technology at all. All that's left are the legs, cut from a piece of 2x2 cedar stock, which will go between the front and the forward brace. I plan to attach them to the forward brace with screws. A stretcher made of a scrap of panga panga will go between the legs at floor level (once again using dovetail joinery), and the rear edge of the top will be screwed to the windowsill.

Did all the machining and a dry-fit assembly today; tomorrow evening we should be able to finish sanding and do the final assembly with glue, and then installation on Tuesday evening. Should be just in time for the cooling season to start. All I have to do after that is get some tubing for the gravity drain, and to make the window panel I was trying to make last year when my table saw shot me.

I even tempted fate by wearing my Wikipedia T-shirt, the same shirt that I was wearing when the saw shot me. There's even a small hole in the shirt where the piece of plywood ripped it on its way to hitting me in the gut. The most serious injury I got out of today's work was a small cut inflicted by one of the chippers in the dado set, while removing it from the saw.

Next weekend's projects include finishing the half-step I mentioned a couple weeks ago, and building an exterior support for the kitchen A/C unit so that it's pitched <i>away</i> from the house instead of toward it like last year. We got a nice puddle in the kitchen from the condensate drain, and I'd rather avoid that this year.