[TowerTalk] Johnson Match Box

[Bill Coleman AA4LR]

On 9/28/00 5:57 PM, K7GCO@aol.com at K7GCO@aol.com wrote:

>Remember the Bumble Bee is not 
>supposed to be able to fly either the Air Flow Math people claim also.  It 
>does indeed fly.

That's not true. That old saw merely points out the fact that early 
models of aerodynamics couldn't account for all flight regimens. 

The reality is that flight for aircraft (from Piper Cub to C5A) is 
different from the flight of very small things like bees. In aircraft, 
one can model the air as a frictionless fluid, and get very reliable 
predictions of performance. In bees, the viscosity of the air becomes 
dominant, and the same models are totally useless as predictors of 
performance.

Reality is that modeling real fluid dynamics is extremely difficult. 
Hypothetical viscosity-free fluids work OK for some aspects, and are easy 
to predict. But real fluids have all kinds of interesting non-linear 
dynamics. Turbulent airflows, like those surrounding a bee's wing, are 
next to impossible to model with current mathematical understanding. 
Maybe in the future, a new type of math will allow us to do so. Not yet.

The situation for electronics is quite different. Models constructed from 
ideal components give usable, real-world values. Sure, those same 
interesting non-linear dynamics exist in electronics, too, but only at 
the smallest, microscopic scales. 

For something like a Johnson Matchbox, anyone talented enough to use a 
Smith chart or run a network analysis can determine what effect the 
split-capacitor has on the matching range. Does this mean that the 
venerable MB can't be used? Heck no. Sure, it will match a bunch of 
antennas. Perhaps it could match more if it weren't for the split-cap, 
but I've certainly seen much more limited, lossy designs work perfectly 
well as a matching network. 

But don't make the mistake of thinking that the MB is perfect. 
Apparently, it's not.





Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@radio.org
Quote: "Boot, you transistorized tormentor! Boot!"
            -- Archibald Asparagus, VeggieTales


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