> When I gave that seminar on SWR to the local club, my
biggest concern was trying to provide a visual image of what
is happening with a transmission line, reflections on the
line, and the resultant loss of signals due to the line
losses. The biggest trouble with this audience is their
virtually complete lack of understanding. Most of the guys
are hamshack on the belt clip types, running mobile VHF gear
and the like. With all of its technical imperfections, the
garden hose analogy allowed me to explain to these young
recruits, in language they understood, why lines generally
work better when matched with load and source impedances.
That's probably the toughest single thing to give a simple
example of. I've been thinking about this for a couple days
now, and now I only have a headache.
I thought of a rope, where the mass of the rope sets
impedance. I like that about as much as a hose, although it
can show standing waves. (It works OK as an antenna, but not
as a transmission line.)
I thought of a mechanical gear set, where the RPM represents
voltage and torque current, but it fails to act like a
transmission line....only like a matching system.
The clearest thing I ever saw was when I was ~13 years old
W8MUK Glen Ingersol from Selectronics in Toledo, Ohio came
to our club in Genoa with a tube type UHF high power
oscillator. With a bunch of light bulbs and rods Glen made
stubs, open wire lines, antennas (including beams), matching
systems, and so on. He would move light bulb indicators
around (neon and incandescent) the system and you could see
the ratio of voltage to current at any point.
It captivated everyone, including the alarm system of a bank
15 years later when I used the same gear (raw AC on the
plate of a dual tetrode oscillator running red hot anodes on
the 4-65A's!!) for our club.
If anyone has any thoughts of a good demo, contact me off
list. Other than a real setup, everything seems woefully
misleading.
73 Tom
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|