Add more Adams-ish snark to why-signals-bend

content/blog/why-signals-bend.md

@@ -20,7 +20,7 @@ Two antennas, flat ground, a hill in the middle. If the hill sticks above the li
 
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-That model is how nearly every commercial point-to-point microwave link is designed. WISPs, utility SCADA, carrier backhaul, all of it. It hides two small lies that the rest of what follows is mostly about. The Earth isn't flat, and the signal isn't a line.
+That model is how nearly every commercial point-to-point microwave link is designed. WISPs, utility SCADA, carrier backhaul, all of it. The model is accurate enough that entire industries have been built on top of it, which is a minor miracle, because it rests on two small lies it would prefer nobody mention. The Earth isn't flat, and the signal isn't a line.
 
 ## Earth gets in the way too
 
@@ -28,7 +28,7 @@ Zoom out far enough and the ground curves. From an antenna of height *h* the geo
 
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-No mast is tall enough to beat that on its own.
+No mast is tall enough to beat that on its own. The Earth has spent four and a half billion years being round and is unlikely to stop on anyone's account.
 
 ## The signal is fatter than a line
 
@@ -38,11 +38,11 @@ The ellipsoid is fattest at the middle of the path. Its radius there is √(λ*d
 
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-This is why microwave links behave so much worse than HF over the same obstructed path. Higher frequency, skinnier ellipsoid, easier to clip with a ridge that doesn't look like much on the path profile. The ridge does not care how it looks on the path profile.
+This is why microwave links behave so much worse than HF over the same obstructed path. Higher frequency, skinnier ellipsoid, easier to clip with a ridge that doesn't look like much on the path profile. The ridge does not care how it looks on the path profile. The ridge is, in fact, indifferent to every document that has ever been written about it.
 
 ## Ridges leak signal
 
-When the line of sight is fully blocked, a sharp ridge doesn't eat everything. The wavefront hitting that edge keeps going, and some energy diffracts into the shadow. The usual way to describe it is the Fresnel-Kirchhoff parameter ν, which mashes together the geometry and the wavelength. ITU-R [P.526](https://www.itu.int/rec/R-REC-P.526/) gives the loss curve, shown on the right.
+When the line of sight is fully blocked, a sharp ridge doesn't eat everything. The wavefront hitting that edge keeps going, and some energy diffracts into the shadow. The usual way to describe it is the Fresnel-Kirchhoff parameter ν, which mashes together the geometry and the wavelength into a single dimensionless number with the virtue of fitting on one axis of a graph. ITU-R [P.526](https://www.itu.int/rec/R-REC-P.526/) gives the loss curve. ITU publications are not known for brevity, but they do, eventually, tell you what you need to know.
 
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@@ -96,7 +96,7 @@ A [*duct*](https://en.wikipedia.org/wiki/Atmospheric_duct) is a layer of atmosph
 
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-Green paths in the scene are the rays (ray = the direction the wavefront is traveling) that stay trapped inside the duct. Orange ones escape. The "critical angle" is the elevation window that stays trapped, and it's tiny, usually a fraction of a degree. That's why ducting is so fickle. Your antenna has to be radiating useful power inside that window, *and* the duct has to exist above your station, *and* the station on the other end has to be inside it or close enough for its energy to enter, *and* the duct has to be thick enough in meters to actually trap whatever wavelength you're running. When all four line up, your 10 GHz rig works a contact 400 km away. When any one of them is off, the path behaves the way the terrain profile says it should, which is to say, not at all. The atmosphere is happy to support this arrangement, briefly, before rearranging itself into something less interesting.
+Green paths in the scene are the rays (ray = the direction the wavefront is traveling) that stay trapped inside the duct. Orange ones escape. The "critical angle" is the elevation window that stays trapped, and it's tiny, usually a fraction of a degree. That's why ducting is so fickle. Your antenna has to be radiating useful power inside that window, *and* the duct has to exist above your station, *and* the station on the other end has to be inside it or close enough for its energy to enter, *and* the duct has to be thick enough in meters to actually trap whatever wavelength you're running. When all four line up, your 10 GHz rig works a contact 400 km away and you feel briefly invincible. When any one of them is off, the path behaves the way the terrain profile says it should, which is to say, not at all. The atmosphere is happy to support this arrangement, briefly, before rearranging itself into something less interesting, usually right around the time you reach for the microphone.
 
 The reframing buried in that list is the one I keep coming back to. "Is there a duct, yes or no" is a surprisingly bad predictor of whether a 10 GHz contact will work. In the contact logs we've collected, the median distance on days with a duct and the median on days without one are almost identical. What actually correlates with distance is the *magnitude* of the gradient, the *thickness* of the trapped layer, and how well that thickness matches the wavelength. The same inversion that supports 1 GHz beautifully might do nothing at 24 GHz because it's a few meters too thin.
 
@@ -148,7 +148,7 @@ A few things I didn't expect going in, now painfully clear from the data.
 
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-Troposcatter is the floor under all of this. The average blocked path is 36 dB down from free space, and realistic duct enhancement caps out around 14 dB. The paths still close anyway. The gap gets made up by forward-scattered energy bouncing off small-scale refractive irregularities in the troposphere, which is present all the time. Ducting is the spike on top of the troposcatter baseline, not the only mechanism in play.
+Troposcatter is the floor under all of this, and fortunately the floor is higher than the arithmetic suggests it has any right to be. The average blocked path is 36 dB down from free space, and realistic duct enhancement caps out around 14 dB. On paper these numbers add up to the paths not working, which would be a compelling argument for abandoning the hobby, except that the paths work anyway. The gap gets made up by forward-scattered energy bouncing off small-scale refractive irregularities in the troposphere, which are present all the time whether you need them or not. Ducting is the spike on top of the troposcatter baseline, not the only mechanism in play.
 
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