Two-meter radio instead of cell phone

A recent search term that brought someone to my blog was "2m radio instead of cell phone". I touched on this topic somewhat in a previous post. However, I didn't talk about particular topic in much detail. There's a whole bunch of differences between using a two-meter handheld for personal communications, and using a cell phone for personal communications.

First, let's ignore the presence of infrastructure. In the absence of infrastructure, the two-meter HT is a lot more useful, but only because the cellphone is just about useless. The only way I could communicate with my cell phone in the absence of service (other than throwing it like a rock) would be to use its flashlight to send messages in Morse code. The HT, on the other hand, will be useful even in the absence of any infrastructure to communicate with someone else (within a relatively small distance) who also has a two-meter HT, in what is known as "simplex mode". So in the no-infrastructure case, the HT wins easily.

But that all changes once you bring infrastructure in. The "ordinary" infrastructure that one would have access to with a HT would be a two-meter FM repeater. There's a lot of these out there, although there's no coordinated way to find out other than looking up your location in a database. Most notably, the HT won't find one on its own; the operator will have to know from a third party database what frequency and squelch tone are required to access the repeater. Also, the person you want to talk to will also have to be listening to that repeater (and not some other repeater), which means they'll have to be somewhere within that same repeater's geographic coverage area, typically a range of 30 to 50 miles. On the other hand, the cell phone allows you to talk to anyone with a phone (cell phone or not) anywhere in the world, knowing only their phone number. Neither you nor they need to know which cell tower you're using. The network takes care of all of this. There are technologies that exist in ham radio that bring the 2m HT closer to the cell phone, things like autopatches and repeater linking, but autopatches are increasingly less common (mainly due to cell phones) and repeater linking not widespread enough to come close to the capabilities of the commercial cell phone networks.

In addition to the above, there are several other major differences. The cellphone is private (encrypted with newer standards), full-duplex (both sides can talk simultaneously), and exclusive (you do not share your channel with anyone else). None of these is true of the amateur HT. All communications on a HT (whether simplex or through a repeater) are over public, unencrypted channels as encryption is forbidden (with only two exceptions) in the amateur service. Typical amateur handhelds are half-duplex only, which means you can either talk, or listen, but not both at the same time. There is no practical way to do full-duplex within a single band; the filtering required would be technologically challenging to put into a handheld device. Finally, you will be sharing the frequency and the repeater with whoever else might be using it.

In short, the 2m HT is no substitute for a cell phone in ordinary circumstances. There's only two ways in which the HT is superior: it works, at least somewhat, even when you don't have an available cell network, and you don't have to pay for a service contract in order to use it. It's the former that makes the HT extremely valuable when you're off in a remote area or during a communications emergency.

The main value of having all these hams with handhelds out there is so that when there is a disaster, there will be people out there with the equipment and the experience needed to effectively provide emergency communications. Otherwise, it's pretty much just fooling around with radios. Which, to be fair, is a great deal of what hams do.

More on sliding dovetails

I finally got around to taking pictures of the two most recent carpentry projects.

The first is the step. The top is made of three planks of four-quarter panga panga, edge glued. The edges are rounded over above and below with a quarter-inch roundover on three sides; the side to the rear has merely had the edges broken. The sides are also cut from panga panga. The underside of the top has a double-blind groove cut to receive the front, which is correspondingly notched to fit into this groove. In addition, sliding dovetail dados are cut in the underside of the top and in the back of the front to receive the sides. To assemble, first the sides are slid in on their sliding dovetails, and then the front slid up on the dovetails cut in the front of the sides until it nestles in the groove in the underside of the top. That's it; the machining is tight enough that no glue is needed. All surfaces are finished by random sanding to 220, and then two coats (sides and front) or four coats (top) of a 50/50 mix of tung oil and citrus solvent. There is no back; however, the entire assembly rests on top of a core made of solid cedar 4x4s endcuts, glued together in a three by ten array. Nonslip shelf covering is above and below the cedar core for cushioning and to reduce slippage (which is nonexistent).

The second is the air conditioner stand, which I wrote about previously. The visible parts are made of standard-quality 12x1 pine planking cutoffs, except for the legs which are 2x2 cedar, and the stretcher at the bottom of the legs, which is panga panga. The table top, which cannot be seen in the photo, is a sheet of four-quarter melamine with a simulated pine finish. As it stands this project is still not entirely finished; the surfaces have only been sanded to 150 and no finish has been applied, the legs have not yet been mechanically attached (although it barely seems to matter), and we plan to put some sort of trim along the top to hide the relatively ugly ship-lap joinery between the sides and the front.

There's also a bunch of flower photos which I've uploaded to Flickr. Feel free to browse and enjoy.

Connecting to the Internet with Amateur Radio

Yes, a lot of people seem to want to do this. ICOM even claims that you can do it using D*STAR, although they're kinda vague on how it works. There are a few problems with doing so. The most commonly cited one is the "third party rule" (§ 97.115), but this actually isn't a major obstacle in most cases; the real obstacle (in the US, at least) are the list of "prohibited communications" in § 97.113.

The third party rule, as implemented by the FCC, only comes into play on international communications; that is, when one of the two amateur stations in the communication is in the United States (or other area regulated by the FCC) and the other station is not so located. So the third party rule would be a problem if you were in the US and trying to use a radio to communicate with a station in, say, Germany, and then from there to connect to the Internet. However, if both of the stations involved are in the United States, this doesn't come into play. The third party rule says nothing about where the third party in the communication may be located; as far as the radio regs are concerned, it doesn't matter that you're going to a website in Armenia, as long as your radio communication isn't going there.

However, the real problem is that any connection to the Internet would have to be continuously supervised to ensure that no prohibited communications took place over the link. And there are so many things that are prohibited: music; anything encrypted; any message in which the operator has a pecuniary interest other than the occasional sale of radio equipment; obscene or indecent language. Imagine how hard it would be to avoid all of these while browsing the Internet.

On top of that, there's the general prohibition in § 97.113(a)(5) on "[c]ommunications, on a regular basis, which could reasonably be furnished alternatively through other radio services." There are plenty of alternative services that can provide mobile connections to the internet, in most circumstances, at least. There's probably a few edge cases where this won't get in the way (out of the way areas, or during a communications disaster).

The problem that this creates is that the only time that the regulations really allow a ham to connect to the Internet would be during a communications disaster. But because we aren't allowed to do it under ordinary circumstances, there's not a whole lot of incentive to have the equipment and infrastructure in place to do it in the event that we do need it. And once-a-year drills on Field Day aren't really a good test of how the system would perform in an actual emergency. We've become increasingly dependent on the Internet for ordinary and extraordinary communications needs; it's almost certain that in a major disaster getting Internet access active in a disaster zone is going to be a priority, and the FCC, by not letting us do this during non-emergency conditions, makes it that much less likely that we'll be able to when it really does matter.

The other day I came across this old article from 2001 about an effort by hams to provide a backup Internet infrastructure using ham radio services. I don't think they're still around; a search for their organizational name (the Emergency Communications Network) turns up only a company in Florida that seems to be providing telephone-based emergency communication services. (Fat lot of good that'll be during a telecom emergency when the telephone network is down.) I have no idea what happened to them or their idea.

So, the long and the short of it is basically that you really can't use ham radio to connect to the Internet... but we would probably be better off if you could.

Two meter handheld range

Here's another post inspired by a search hit. Some fine soul hit my blog today on a search for "expected range on a 2 meter handheld radio". This search would have brought our feckless reader to this post, which does not fairly answer the question. So, in the hopes that the next person to do this search actually learns something, I'll essay to answer this question.

The answer, of course, is "it varies". The amateur radio two-meter band is a VHF band, and as such is almost entirely line of sight. (Sporadic E skip, tropospheric ducting, meteor scatter, auroral skip, and earth-moon-earth are all quite difficult with an HT, so I won't dwell on them here.) So, basically, the range of any 2-meter radio is going to be limited by the horizon. However, because the atmosphere refracts radio waves considerably more than it does light, the effective radio horizon is about 15% further than visual horizon. So that establishes one of the limits on range: the receiver at the other end must be above the effective horizon. This is a function of four things: the altitude above ground of the transmitter, the altitude above ground of the receiver, the distance between the two, and the terrain between the two. The effective radio horizon for a given location, assuming flat terrain, is about 4.11 kilometers times the square root of the height of the antenna (in meters) above ground. So two stations with their antennas each one meter above ground will be in each others' horizons if they are closer than about 8 kilometers (a typical handheld-to-handheld case). If one of the stations is, instead, a repeater with its antenna 60 meters above ground, the range is nearly 36 kilometers. If one of you is atop the John Hancock Center in Chicago (344 meters), the range would be a whopping 80 kilometers. Of course, all of these are assuming flat terrain; if one of you in on top of a mountain, then that will also increase range, and if there's a mountain between you then you will be out of luck.

This isn't the end of the discussion, though. Not only do you have to have to be within each other's radio horizons, you also have to have enough power to survive path loss. Path loss represents the reduction in strength of the radio wave as it travels through space. Much of this is simply due to the inverse square law: as the wavefront grows in size, it occupies more space without having any more power, and thus has a lower power density. The receiving antenna's size doesn't change, so if it's moved further away it will receive less of the transmitted field. This is "freespace path loss", and if this is all you were facing loss would simply double twice with each doubling in distance (a loss of 6 dB for each doubling in distance, or octave). However, in real situations, other factors also contribute to loss, and in average conditions the effective loss in VHF is closer to 7 dB per octave, with a base at 1 km of about -71 dB. Most HTs will be able to just barely receive a signal at about -120 dBm, and should give suitable performance at about -100 dBm. This means that at 1 km, to have acceptable performance, you'll need to transmit a signal of -29 dBm. That's not even two microwatts. (In practice, you wouldn't get that far on two microwatts, because your HT's antenna probably sucks. More on that below.) Even at the 80 kilometers long-range case above, the path loss is only -115 dB; a signal of 15 dBm, or about 30 milliwatts, would be sufficient. Even with antenna losses, that's possibly within the typical 5 watt (37 dBm) capabilities of your average HT.

However, this discussion ignores one critical factor: the poor antennas that most HTs have. In practice the antenna of a handheld radio has negative gain in most operating environments, and you can expect to lose anywhere from 2 to 5 dB due to this issue alone. Obstacles (other than terrain) can also wreak havoc with the signal; if you're in a car, for example, expect to lose as much as 20 dB due to absorption from the car; other things that can reduce range include trees and buildings. Also, when transmitting within one wavelength of the ground (which for an HT is almost always) a significant portion of the signal is lost into the ground; this can account for up to 10 dB of loss.

However, it remains the case that in almost all cases, radio horizon, and not power, is the primary limitation on VHF range. So, in ordinary conditions, your 2m HT range is going to be about 8 km HT-to-HT simplex and about 25 to 40 km HT-to-repeater (depending mainly on the height of the repeater's antenna).

P.S. All numbers in this article may be wrong. I've tried to get them right but it's late and I may have made mistakes. If you do spot anything wrong, please feel free to hit me.

Too many repeaters

Is there some law that requires ham radio sites to have atrocious web design? Some of the sites I've been at recently (and I won't name names, not right now) have just horrible web design. Blinky graphics, animated horizontal rules, busy background patterns... it's Geocities all over again!

One thing that I've been frustrated by recently is the lack of useful repeater listings for Chicagoland. Most of the listings I can find just list the city or town for the repeater. This is multiply frustrating for me where I am. First, there are just dozens of little suburbs around here, many of which the names of which I forget, and scanning a list of repeaters in Illinois sorted alphabetically for the ones near me is challenging and tedious. Second, a repeater in Chicago may or may not be close enough for me to use; Chicago is a big city and a repeater might not cover the entire city if it's not high enough or is on the wrong side of the Sears Tower or something. Third, many repeaters are listed with a city/town of the residence of the operator or the trustee, not the actual location of the transmitter (which may be miles away and several towns over). K5EHX's repeater list tries to rectify this somewhat, but this database suffers from the fact that most of the repeaters have only a default lat/long of the city center of the listed city (which, as noted, may be incorrect). (Not K5EHX's fault; he can't create data out of thin air anymore than anyone else can.)

I am therefore going through the list of repeaters for my location, trying to update the information as best I can, using the web and emailing operators to the extent possible, and going on air to try to get info when I can't find the info via the web. This is proving to be tedious, but at least it will hopefully help someone.

If you know a repeater that isn't listed in K5EHX, or is incorrect, please add it/fix it as appropriate! Chicagoland isn't the only place where this data needs work.