Observations made while driving back from Defcon

I often listen to the radio station 93.1 JACK FM, which plays a lot of kinds of rock. In Las Vegas, however, 93.1 is The Party and plays dance music. Driving from one city to the other, there was a part in the middle where I could pick up both stations, which was pretty strange. I only got one of the stations at a time (with intermittent static), but they would switch off. I believe that when driving uphill I could get the Las Vegas station, but driving downhill I picked up the Los Angeles one. Can any physicists/electrical engineers explain why this might happen? It sounded like a bad DJ with poor taste was trying to make a remix of Independent Woman by Destiny’s Child and Poison’s Once Bitten, Twice Shy. It was bizarre.

I spent a lot of the trip on a two-lane highway through the desert, stuck in all the traffic commuting from Las Vegas back to Los Angeles. The heavy traffic displayed an unusual phenomenon, however, which I found fascinating. All of the trucks were in the right lane, as is their custom. All of the speed demons were in the left lane, as is theirs. However, due to the heavy traffic, no one was going much more than 20 mph at the most. However, the trucks, which, due to their weight, had trouble accelerating and decelerating, were trying to stay at a constant speed: they would keep a lot of space in front of them, and close this gap when the traffic in front of them slowed down (and then increase the gap as the traffic sped up). The left lane, however, vacillated between going 40 mph and being at a standstill. After the traffic in front of a car picked up, however, it would take a moment for a car to pick up and start moving again (the same problem the trucks would have had, but on a smaller scale). Consequently, the right lane, with its slow-but-steady trucks, was actually moving faster than the zippy sports cars in the left lane. I noticed this, switched to the right lane, and was amazed at how quickly I passed cars in the other lane: 4 of them would pass me, then their lane would come to a stop, and I would pass 10 of them, and this cycle repeated through the whole desert.

This behavior reminded me of Robert H. Frank’s book, The Economic Naturalist. In it, he applies economic principles to non-economic parts of life to make sense of the world around us. He describes many situations in which a certain behavior gives an individual a benefit but detracts from the group as a whole. For instance, male elephant seals compete for dominance in their territory, and then mate with the females in the area. Typically the larger male wins any dispute over territory, so the males have evolved to be larger and larger over time. They have now gotten so big that they must mate on their side, since a male would crush a female if he tried to mount her. The cars in the left lane were another example of the tragedy of the commons, and I was proud that I recognized and avoided the situation.

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  1. krustad says:

    Not an engineer, but presumably the hill is enough of an obstacle to radio waves that it causes the unblocked rival signal to dominate. On the east side of a hill (uphill) the LA station’s signal has to go through the huge mound of dirt while the LV station’s signal does not. Vice-versa on the west side of the hill (downhill).

    • dhalps says:

      There is a PLL (phase-locked loop) that locks on to the strongest signal, and due to different frequency offsets between your car and the station, you’ll really only lock onto 1 of the two at once. And yeah, when you’re going uphill your car only has line of sight to Vegas, and downhill LOS to LA.

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