None of the esoterica below should worry anyone who just wants to hook up a
wire to his radio and listen to shortwave stations.


"John Doty" wrote in message
...

For a wire antenna, the field configuration near the wire is very
similar to the field inside a coaxial cable. Unsurprisingly, it has
similar behavior: the bulk of the energy tends to propagate along the
wire and not radiate. This leads to Schelkunoff's approximation: you
calculate the current distribution along the antenna as if it was a
transmission line, and then calculate the radiation due to that current
distribution. You can get the antenna impedance by calculating the
impedance of a lossy transmission line (with loss equal to the
radiation) with the assumed current distribution. You get the reception
properties by reciprocity.

OK, but if the transmission line analogy holds, shouldn't the unterminated
antenna look like a lossy stub? If a stub is open, it will look like an
open or short at certain frequencies, and some sort of reactance at others.
Of course, if the transmission line/antenna is terminated with it's
charactistic resistance, it will look flat.

Since the formula isn't frequency sensitive, I was wondering if it was for
terminated wires.


Good thing. Even when the rocket fails and destroys your payload, you
get to go home and hug your wife and kids. It's happened to me twice so
far (HETE-1 on a Pegasus in 1996, and ASTRO-E1 on a M-V in 2000).


Have you seen the movie "Cape Canaveral Monsters"?

Frank Dresser

Frank Dresser wrote:
None of the esoterica below should worry anyone who just wants to hook up a
wire to his radio and listen to shortwave stations.


"John Doty" wrote in message
...

For a wire antenna, the field configuration near the wire is very
similar to the field inside a coaxial cable. Unsurprisingly, it has
similar behavior: the bulk of the energy tends to propagate along the
wire and not radiate. This leads to Schelkunoff's approximation: you
calculate the current distribution along the antenna as if it was a
transmission line, and then calculate the radiation due to that current
distribution. You can get the antenna impedance by calculating the
impedance of a lossy transmission line (with loss equal to the
radiation) with the assumed current distribution. You get the reception
properties by reciprocity.


OK, but if the transmission line analogy holds, shouldn't the unterminated
antenna look like a lossy stub?

Exactly!

If a stub is open, it will look like an
open or short at certain frequencies, and some sort of reactance at others.

If it's lossy, the terminal impedance of an open stub will have a
resistive component at all frequencies. A good first approximation for
an inverted L is a 500 ohm line terminated with a 5000 ohm load. Works
pretty well for wires with lengths in the range from 1/4 wavelength to
several wavelengths.

Of course, if the transmission line/antenna is terminated with it's
charactistic resistance, it will look flat.

When you match to the characteristic impedance, you get a nearly flat
frequency response, but it's down by a few dB from what you'd get by
matching to the terminal impedance.


Since the formula isn't frequency sensitive, I was wondering if it was for
terminated wires.

The characteristic impedance isn't frequency sensitive. The terminal
impedance is. Just like a stub.



Good thing. Even when the rocket fails and destroys your payload, you
get to go home and hug your wife and kids. It's happened to me twice so
far (HETE-1 on a Pegasus in 1996, and ASTRO-E1 on a M-V in 2000).



Have you seen the movie "Cape Canaveral Monsters"?

Nope.

-jpd

"John Doty" wrote in message
...
[snip]


Since the formula isn't frequency sensitive, I was wondering if it was
for
terminated wires.

The characteristic impedance isn't frequency sensitive. The terminal
impedance is. Just like a stub.


I gotcha. I thought the formula was supposed to show a flat terminal
impedance from an end fed wire. I was confused.

By the way, Reg Edwards has some small design programs on his website. One
of them is on topic for this thread. It's called ENDFEED:

http://www.btinternet.com/~g4fgq.regp/page3.html#S301"



Good thing. Even when the rocket fails and destroys your payload, you
get to go home and hug your wife and kids. It's happened to me twice so
far (HETE-1 on a Pegasus in 1996, and ASTRO-E1 on a M-V in 2000).



Have you seen the movie "Cape Canaveral Monsters"?

Nope.


CCM features bickering aliens and both radio and radium! Who could want
anything more? Aside from the narrow minded goofs who list CCM as the worst
movie ever made, that is. I've seen CCM at least half a dozen times and I'd
be watching it right now, if it was on TV. Unless "Hot Rods to Hell" was
on. Anyway, there's a wordy synopsis of CCM he

http://www.jabootu.com/acolytes/bnotes/ccmonsters.htm

Frank Dresser

In article , "Frank
Dresser" writes:


Have you seen the movie "Cape Canaveral Monsters"?

Frank Dresser



No..

"- Look! What's This?? "

"Theres something out there.
we should go Investigate.."

Dr. Baugh : ": " Helen, You Stay Here, Brick lets see whats causing that noise"
Maggy ( Obviously a Mammal) No Baugh, I'm going with you..,
I don't want you going out there with Brick in the dark.."

http://www.jabootu.com/acolytes/bnotes/ccmonsters.htm

& BTW
Here's a good " Noir" list

http://www.aint-it-cool-news.com/display.cgi?id=17903

"Diverd4777" wrote in message
...
& BTW
Here's a good " Noir" list

http://www.aint-it-cool-news.com/display.cgi?id=17903




SWLs may have an interest in Atomic Movies. Atomic Movies combine two of
our favorite elements, International Diplomacy and Armageddon.

Here's a list of Atomic Movies:

http://www.conelrad.com/conelrad100/

The movie list is presented by conelrad.com, which was named after the radio
system which was supposed to keep us up to date on WW3 while simultaneously
confusing the radio navigation of Soviet A-bombers.

Frank Dresser