The Mojave Phone Booth

I stumbled on this link when engaged in some otherwise pointless search on-line for something entirely different.

Like my desert-dog buddies, Bart R., Pete C., Greg M., and others, we all had our adventures wandering around the Mojave Desert as kids and then young and not-so-young adults. Some more than others.

The string (yes, there’s more than one) of phone booths in the Mojave was one of those fascinating, improbable, and curious marks of humanity and technology in an otherwise fairly natural and wild scene. The first time I stumbled across one was in a weekend adventure with Bart.

We’d been up in the Mountain Pass area, I think trying to suss out the Kokoweef mine/cavern mysteries, and decided to venture south into the Landfair Valley. We’d seen on the topo map an old railroad grade heading up a canyon from Ivanpah, and a bunch of old mines in the area, so it looked worthy of a visit.

Working our way up the path through the New York Mountains, passed intermittent signs of humans, some very abandoned, others fairly fresh. There were the occasional cattle, and sometimes a corral or stock tank. Even more rarely, there was what looked to be a cluster of buildings like a ranchhouse, but not much in the way of people.

Arriving at the north end of the Landfair Valley on the Goffs-Landfair-Ivanpah Road (aka Landfair Rd), it was just miles and miles of miles and miles of empty, serene desert. It was winter, so there were signs of some recent and rapidly vanishing snow over on Drum Peak, the high point at the west end of the New Yorks, and even some on the Mid Hills, to the southwest of Drum.

Anyway, we ambled along down the road until we discovered our improbable phone booth, either at the intersection of Old Government Rd or the intersection with Cedar Canyon Rd.  I’m sure that perhaps somewhere I have my own photo of it, but there are many photos of one of the booths and the surrounding desert available on the inter-webs!

Stopped and picked up the handset, and lo and behold, a dial tone. Pretty cool. We saw a sign adjacent cautioning about digging and damaging a cable underground, so it appeared that the phone may get its connection from the underground cable.

Once we got back to LA and to work the next week, I was determined to figure out how to call that phone booth and why it was there. Set me on a mission to find someone somewhere who knew. First stop was dialing “0”.

Nice operator answers, I tell her that I’d like to call this phone booth in the middle of the desert, in the Landfair Valley. I think she hands me over to a super-operator, or or maybe there’s a couple of handoffs, but ultimately I get to speak to a lady who seems to know how to contact the phone there. Sadly, I have no documentation now on this exploration from 40 years ago, but it was pretty awesome, as far as I can remember. First, that a snotty-nosed 20 year old kid could call the OPERATOR, and there was someone there who could navigate me through the arcane world of party lines and microwave links that somehow got to that one spot in the desert, and spend an hour doing it; second, that she then handed me over to someone at AT&T Long Lines (an engineer, I am pretty sure) who was excited to find a young person who was actually interested in their arcane but extremely vital universe of long-distance telephony and data communications; and finally that doing this didn’t trigger all sorts of alerts and alarms that I was interested in things like this. In today’s atmosphere, it seems like an invitation from the MIB or worse.

The story I got was that the booth was there because of tariff/regulatory rules. There was a long-distance underground cable buried there, along the old Government Road, and the rules required a public access for phone service no less than every 20 miles. This happened to be an empty spot in the desert where there were a few people living, there was a major road through here, so they put the booth there.

At this time, there wasn’t a direct-dial number for the booth, it was something like having to talk to a special operator and then asking for “Landfair 1”, or something like that. Awesome!

A solar-powered AC outlet. I kid you not.

Ok, so you think you’ve seen it all, and that there’s all this massive amounts of free (well, nearly) energy just streaming down on you from that big nuclear-powered star up there. This gadget is pretty novel, and pretty lame.

It’s around a 10 cm flat cylinder with an AC outlet on one side, and a teeny-tiny solar panel on the other. The panel has enough surface area that the vendor claims it can fully charge the 1000 mA-h battery inside the gadget to a full charge in 5 to 8 hours. The vendor then claims that the battery can last 10 hours (I’m assuming in discharge mode).

Fact check – let’s try to calculate the amount of power available from the gadget’s solar panel assuming a perfectly clear day and the gadget oriented so that the solar panel remains normal to the sun all day. The panel looks to be perhaps only 0.1 m across, and using 2πr^2, with r = 5 cm, the panel surface area is around 0.015 m^2. The highest solar insolation at the earth’s surface is less than 1100 w/m^2, and the solar panel is unlikely to have more than at 15-20% efficiency – let’s give it the benefit of the doubt and say 20%. That means that the solar panel, perfectly oriented and tracking the sun can generate about 0.015 m^2 * 0.20 * 1100 W or about 3.3 w of power. If the battery is really a 1000 mA-hr battery, and the gadget takes 8 hours max to charge to full, then the voltage on it needs to be about 25 vdc to make 25 w-hr of storage. And given all the inefficiencies, the battery voltage is likely more around 3.7 vdc (single Li cell) or 7.5 vdc (2 Li cells), in order that the “charges in 10 hours” claim can hold true.

That’s a pretty generous estimate, and not even considering the deleterious effects of the 80% of the sunlight that didn’t get converted to electricity by the solar panel, and instead just added a heat load of 15 watts to the little gadget, heating up the battery and charging circuit to uncomfortably high temperatures and reducing the battery and circuit life.

Over an 8 hour day, this is only 25 or so watt-hours. And in the real world, where (as the vendor suggests) the gadget is charged by sticking it to an outside-facing window the likely energy collected is going to be way less than that. I’d say maybe 10-20% of the best-case energy. But let’s ignore that big loss in efficiency for now.

So 25 w-hr, converted to 220 vac 50 Hz using a 95% efficiency converter,  means that this gadget can supply enough power over the advertised 10-hour full charge period to power “not much”. The calculation is

0.95 * 25 w-hr / 10 hr = 2.4 w continuous at 220 vac

A PC, iPad, iPhone or other smart phone-type device can’t even be fully charged using this gadget.  Another way to look at it is that an iPhone has a 4 vdc, ~ 2000 mA-hr battery, and this gadget’s battery is about half that in capacity. So it can’t even charge an iPhone fully, and in fact throws a lot of energy out the window due to the multiple conversions.

However, I will say that it would be pretty cool to see a power outlet stuck to a glass window with no other attachments, and the ability, even for a few minutes, to be able to plug in a load (like a computer or a light bulb) and amaze your friends that it can be powered. Like all magic tricks, you can only make it work under very controlled conditions and with a minimum of scrutiny.

It’s gadgets like this that give engineering a bad name.


Freezing water when it’s not freezing outside

Ok, it took forever to get the blog running again, but today I’m playing with temperature and the dark sky. I don’t have a lick of math to back anything up (yet), but here’s what I’m seeing.

I have a cheap weather station (from Costco) .Img_3736_small

This wx station comes with an “outdoor” temperature sensor.


I also have a near dead-flat white foamed roof on the house (seen in the background of the sensor above). I remember a long time ago one of my great mentors Bart telling me about the ability to use the cold of deep space to freeze water outside even when the air temperature is above freezing.

I’m here in the desert, and it’s fairly dry atmosphere. The ambient air temperature (as measured by the Davis wx station about 8 m away and 2 m higher)


is 47F (281K) right now, and the sensor sitting on the roof is showing 27.3F (270K). So 11K colder. Early this morning, when the outside air temp was 272K, the roof top sensor was showing about 264K. Hard freeze temperature. If I put a pan of water on the roof next to the sensor, it will be a disc of ice in the morning. Pretty neat!

So, how’s this work? I suspect that the hemisphere of sky that the sensor is exposed to above is pretty cold, significantly more than the 3K of the CMB but not anywhere near ambient air temperature. There’s a few palm trees that stick up into that hemisphere, but that’s a small portion of the overall scene, and palm trees probably don’t have a lot of heat contribution, though they do reflect the ground, which is currently over 273K. Since the atmosphere is fairly empty, there’s not a lot of heat energy between the roof and space – it’s a clear night. That lack of heat means that there’s probably not a lot of energy to illuminate my temperature sensor laying flat on the roof. So, for that hemisphere (at least), the heat energy available is pretty low.

Now on to the other hemisphere, the one below the sensor laying flat on the roof. Well, it’s all white foam and provides a pretty good insulation from the heat of the house and the ground and shrubberies, etc., nearby. The foam under the white coating is a closed cell yellow foam and probably has pretty poor heat conduction. Given that the foam also is low density, it probably doesn’t have much heat capacity so there’s not much contribution of heat energy from that lower hemisphere, and I imagine it cools rather quickly once the sun goes down.

So, here I’m measuring the temperature at the air layer about 1 cm above the roof, and well below the parapet wall around the roof at about 20 cm. It’s dead still tonight, so there’s little air mixing at the roof level. The Davis wx station uses their usual baffled temperature sensor and is pretty close to the other temperatures measured locally, though I suspect it’s biased a bit by being so close to the roof, and not on a nice piece of open land as per NOAA/NWS siting guidelines.  I’ve got a homeowners’ association to deal with, doncha know…

Anyway, I will try to get some calculations going and see what I should be able to see. If I get very ambitious, I might even build a temperature sensor “tower” that can measure the temperature at a number of distances off the roof (from touching the roof to maybe 100 cm) and see what the gradient looks like.

This also explains why the truck windshield gets frost on it some night but not others. The windshield will chill due to seeing mostly the cold sky, and it will chill faster than the ambient air when there’s little air movement. If the temperature on the surface of the windshield gets below the dew point, then I should see water ice plate out on the windshield. This happened a few nights ago, and the ice was pretty resistant to defrosting.