In article , (GO
BEARCATS) writes:


( I can pick up WWV in Wheeling West Virginia
(And hear " The Coal Mine report" at 10:00 P.M. )

Hey Dan, what's the name of that station and freq that does that coal mine
report?

tx


WWVA, 1170 Wheeling W. Virginia..

http://www.wwva.com/main.html

In article et,
"Sanjaya" wrote:

I have a 50 ft. random wire (22 AWG) I use for my portable SW's. It
is indoors and just runs around the ceiling of my listening room.
Connects to the receivers with a 1/8th inch mono plug.

Now I'm looking at the Icom IC-R75 and see it needs a 500 ohm
longwire.

Is there a way to convert my random wire to function properly with
the Icom. That is, can I make it a 500 ohm wire? Alternately, can I
take it down and replace it with another wire. Since I don't know
sh*t about antennas, what makes a wire 500 ohms, and what parts,
besides the proper gauge wire, are needed?

Presently I have to keep this simple, since I can't put anything up
outside. If I move I could put up a "real" antenna outdoors, but if I
get the Icom now I'd need to use basically the same setup I use for
the portables.

Should I forget the Icom until I have a new house? Geez... then I'd
have a $100,000 shortwave radio.

If you want to e-mail a reply instead of post you can send it to
sanjaya_49 at yahoo dot com

For a random wire the RF return is the ground underneath the wire. The
farther the wire is from the ground the higher the impedance. The
smaller the diameter of the wire the higher the impedance. The lower
the conductivity of the earth under the wire (generally) the higher the
impedance of that wire.

For average earth conductivity and a 22 gauge wire the height above
ground for 500 ohms impedance would be less than 5 foot and most likely
you would want it around 2 to 3 feet off the ground.

--
Telamon
Ventura, California

Telamon wrote:



For average earth conductivity and a 22 gauge wire the height above
ground for 500 ohms impedance would be less than 5 foot and most likely
you would want it around 2 to 3 feet off the ground.


At what frequency did you calculate this?
-Bill

In article , Bill
wrote:

Telamon wrote:



For average earth conductivity and a 22 gauge wire the height above
ground for 500 ohms impedance would be less than 5 foot and most likely
you would want it around 2 to 3 feet off the ground.


At what frequency did you calculate this?
-Bill

The impedance of the wire is not dependent on frequency.

Z= 138 * log (4* height / wire diameter)

Don't confuse a physical property of the wire with reactance.

--
Telamon
Ventura, California

Telamon wrote:
In article , Bill
wrote:


Telamon wrote:



For average earth conductivity and a 22 gauge wire the height above
ground for 500 ohms impedance would be less than 5 foot and most likely
you would want it around 2 to 3 feet off the ground.


At what frequency did you calculate this?
-Bill


The impedance of the wire is not dependent on frequency.

Z= 138 * log (4* height / wire diameter)

Don't confuse a physical property of the wire with reactance.

Well, you're correct, but. There's more to the antenna than the natural
impedance of the wire alone. You have to look at the 'feedpoint'
impedance which is totally different and thats where you'll find the
reactance which cannot be ignored in actual practice.
Z=R+jX
Thats where frequency gets into the picture and gives you a number to
work with when matching the antenna to your radio.
This is Smith Chart 101...(which I never did too well with)


-Bill

"Bill" wrote in message
...
Telamon wrote:
In article , Bill
wrote:


Telamon wrote:



For average earth conductivity and a 22 gauge wire the height above
ground for 500 ohms impedance would be less than 5 foot and most likely
you would want it around 2 to 3 feet off the ground.


At what frequency did you calculate this?
-Bill


The impedance of the wire is not dependent on frequency.

Z= 138 * log (4* height / wire diameter)

Isn't that a transmission line equation? I found a similar one in Terman's
Radio Engineer's Handbook, which I posted on the alt.binaries.pictures.radio
newsgroup.

Or might the non-resonant formula apply only to terminated antennas such a
beverage antennas? A quick scan through the Terman book doesn't give a
formula for beverage antennas.



Don't confuse a physical property of the wire with reactance.

Thicker wires, at the same center to center distance, have more capacitance
to the other conductor.


Well, you're correct, but. There's more to the antenna than the natural
impedance of the wire alone. You have to look at the 'feedpoint'
impedance which is totally different and thats where you'll find the
reactance which cannot be ignored in actual practice.
Z=R+jX

The radiation resistance (or reception resistance, I suppose) of a wire
shorter than a half wavelength is very low but goes up as the length of the
wire goes up. The reactance goes down as the wire approaches half a wave
length. In effect, they add up to a high number for end fed wires.
Something like the same effect exists above half a wavelength. These
resistances and reactances can be calculated and measured, but there's
little practical reason to do either for reception. The reactance adds to
the resistance, and the impedance can safely be assumed to be "high" for end
fed wires.

Just to be complete, I'll mention that an antenna tuner or balun can more
efficiently match an antenna to a radio. It's not always worth the effort,
however.


Thats where frequency gets into the picture and gives you a number to
work with when matching the antenna to your radio.
This is Smith Chart 101...(which I never did too well with)


-Bill

I don't think I"ve looked at a Smith Chart in 25 years. The average SWL can
do just fine without getting into all the confounding technical details of
the hobby. I think Steve covered the most important part when he wrote that
it's the nature of end fed antennas to have a high impedance.

Frank Dresser

Bill wrote:
Telamon wrote:

In article , Bill wrote:


Telamon wrote:



For average earth conductivity and a 22 gauge wire the height above
ground for 500 ohms impedance would be less than 5 foot and most
likely you would want it around 2 to 3 feet off the ground.


At what frequency did you calculate this?
-Bill



The impedance of the wire is not dependent on frequency.

Z= 138 * log (4* height / wire diameter)

Don't confuse a physical property of the wire with reactance.

Well, you're correct, but. There's more to the antenna than the natural
impedance of the wire alone. You have to look at the 'feedpoint'
impedance which is totally different and thats where you'll find the
reactance which cannot be ignored in actual practice.
Z=R+jX
Thats where frequency gets into the picture and gives you a number to
work with when matching the antenna to your radio.
This is Smith Chart 101...(which I never did too well with)


The fixed *characteristic* impedance of the wire is key to understanding
the feedpoint impedance. If you choose Z0 of your Smith chart to be
equal to the characteristic impedance of the wire antenna, you'll find
that the feedpoint impedance makes a spiral about the center of the
chart as the frequency is varied. This means that the characteristic
impedance (the center point of the spiral) is the best *frequency
independent* match to the wire.

Since for practical configurations the formula Telamon quoted above
yields characteristic impedances in the range of 300-700 ohms, many
receivers have ~500 ohm inputs and many of us use 9:1 matching
transformers when using coax feed.

See http://anarc.org/naswa/badx/antennas/SWL_longwire.html

-jpd