Wednesday, July 15, 2020

Quest: Its a Pickelman

“I give up, what is a ‘Pickelman’?” Sammy asked.

“A Pickelman is a directional microphone*” Dmitri informed him. “More precisely, it is an array of three microphones that use phase information to indicate the direction the sound came from.”

Dmitri pulled one out of his jacket and handed it to Sammy. It was half the size of a 3X5 note card and as thick as a flip-phone.

“How do I use it?” Sammy asked.

“That is where you get to use your imagination” Dmitri informed him. “If it were me, I would deploy them in pairs, like eyes. For instance, if there were three potential mortar sites that are close together, I would consider putting two of them you could monitor all three.”

Sammy scratched his chin, deeply in thought. “How accurate are they?”

Dmitri sighed. “They aren’t perfect. Wind moves the apparent center. If there is no wind...I measured within two-meters at a hundred meters.”

That was...intriguing. A counter barrage of mortar shells could easily span a thirty-meter-by-thirty-meter spread.

“Is there anything else I should know?” Sammy asked.

“They are tuned for 1000Hz” Dmitri said, shrugging. “I had Milo drive by in his truck and that seemed to be the best frequency to following moving vehicles. Then, on the way over, I realized that slow-moving trucks don’t make a lot of noise, so maybe that isn’t the best frequency.”

“Don’t worry. We can work with it” Sammy assured him.

“The other thing is that you can bypass the directional software and listen to the mics directly. But you gotta know, the bandwidth will kill your other communication.” Dmitri cautioned him.

Sammy nodded.

“How many did you bring me?” Sammy asked.

“I only have six” Dmitri said, apologetically. “I thought you needed something to play with while we ramp up production.”

In fact, finding the computer power to process the signals from the three microphones had been a challenge. It wasn’t the computational power, it was finding a unit that had just enough computational power AND low power consumption and then finding a hundred of that same unit.


Dot and Tory took off from the airfield behind Dot’s house. They had a full tank of gas and a short mission so fuel economy was not the primary consideration. Dot took them up to 3500 feet in a rapid climb. Dot weighed about 110 pounds and Tory was 92 pounds of whipcord. The plane was far from overloaded.

The Zenith 701 climbed like a kite in a strong wind.

Reaching 3500 feet, Dot consulted the cheat-sheet she had hand-written and then taped to console above the instruments. It was a sheet of minimum noise throttle settings for a given air-speed and load.

Unlike more sophisticated planes, the Zenith had a fixed-pitch prop. It was not possible to adjust the prop to optimize the “bite” of air it took. Consequently, there were optimum prop-speed/air-speed combinations that minimized the amount of noise the plane generated. That sound could be reduced even further if a very slight glide path were incorporated. The downside of that, of course, is that it would bring the plane closer to ground fire.

But today’s mission started in Capiche and there was little risk of spies or ground fire. Dot let the motor generate horse-power and minimized the time it took to get to cruising altitude.

After reaching 3500 feet above ground, Dot turned east and they cruised across Ingham county in approximately twenty minutes. Approaching the West Branch, Dot throttled back to the minimum noise settings and coasted down to the optimum speed.

Given the visibility of the clear, dry air it was not hard to see a radius twenty times their cruising altitude. That is, Dot and Tory could see in great detail an arc that stretched twelve miles out from the cockpit of their plane. After flying east for an additional fifteen minutes, they had pretty much seen all there was to see in Livingston County.

It had been a decade since Dot had felt this alive.

“Wanna check out Washtenaw County and Ann Arbor?” Dot asked. She felt invisible.

“Sure!” Tory enthused. That is why they had to plane to collect information.

Dot turned south and they floated another thirty minutes in that direction. Tory was glued to the window. She had given up trying to take photos. They were too blurry. She committed what she saw to memory.

Crossing over I-94, Dot gently breathed on the rudder and they sloooooowly turned west, as quiet as a church mouse.

Other than a few scattered gardens, they had seen no signs of agricultural activity in either Livingston or Washtenaw Counties.

Had they been briefed to look for it, they would have noticed the vehicles marshalling in parking lots across Howell.

*For the nerd types: The Pickelman array only monitors one frequency so the FFT can be coded to run with great economy. Further, the mics are placed a quarter wavelength apart to simplify later math.

Moe Pocket's face blew up with the third dose of vaccine.

His nose became massively swollen. His eyes were slits. He had difficulty swallowing and even breathing.

Fortunately, Dr Sam still had a stash of Benadryl. The swelling diminished.

"Well, now what?" the council asked.

Dr Sam was in the hot seat.

"I think we continue with the vaccine program but we dilute all vaccinations after the second one" she replied. "Obviously, he had a huge reaction. His immune system went nuts."

"Doesn't that mean we should stop a the second dose?" Rick Salazar asked.

"That is a reasonable question" Dr Sam admitted. "The problem is that I don't know how much of what Moe reacted to was Ebola-like genetic material and how much of it was random DNA from the host bacteria."

"If we were still a first-world country, I would drop this vaccine but we are NOT a first-world country any more" Sam reminded them. "I think we finesse what we have. Maybe we lower the dose to 10% of the first two and we keep a close eye on the patients."

The council voted unanimously to follow Dr. Sam's recommendation. The second half of the fighters in Capiche and the Buffer-Zone started the immunization program. The first half, the ones who had already had two doses were scheduled for a much diluted, third dose after the required two weeks elapsed.


1 comment:

  1. Ah, some interesting things happening... Ironically, 1000-1200Hz is predominant from vehicles even if they are moving slowly. Harmonics of systems reenforce in that band for 'some' reason... ;-)


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