Adjusting Resonant Frequency
 

Considering a wire dipole (or inverted V) does bending the end of a leg back
and wrapping it around itself electrically shorten the antenna or must it be
cut in order to change the resonant frequency?

if it is insulated wire it must be cut, if its not then it doesn't. though
you will see some effect of folding it back even with insulated wire it
won't be the same as cutting the wire shorter.

"wb5cys" wrote in message
m...
Considering a wire dipole (or inverted V) does bending the end of a leg
back and wrapping it around itself electrically shorten the antenna or
must it be cut in order to change the resonant frequency?

That being the case, can I just keep folding back a 120 foot insulated wire
dipole until it is say 5 or 6 foot long and it will still be resonant on
the original frequency?

"Dave" wrote in message
...
if it is insulated wire it must be cut, if its not then it doesn't.
though
you will see some effect of folding it back even with insulated wire it
won't be the same as cutting the wire shorter.

"wb5cys" wrote in message
m...
Considering a wire dipole (or inverted V) does bending the end of a leg
back and wrapping it around itself electrically shorten the antenna or
must it be cut in order to change the resonant frequency?

On Thu, 16 Jun 2005 09:56:24 -0400, "Fred W4JLE"
wrote:

That being the case, can I just keep folding back a 120 foot insulated wire
dipole until it is say 5 or 6 foot long and it will still be resonant on
the original frequency?

"Dave" wrote in message
...
if it is insulated wire it must be cut, if its not then it doesn't.
though
you will see some effect of folding it back even with insulated wire it
won't be the same as cutting the wire shorter.

No one said it would be resonant on the SAME frequency, just that
there will be some effect. I have heard about an antenna design for a
shortened dipole using 3-conductor home electrical wire. At one end,
the green is connected to the cobra-head and the black and white wires
are soldered together. At the other end, the black is soldered to the
green. Viola -- a linear loaded dipole!

I haven't tried it, but if it works, you may very well get your
desired frequency with folded wire. I would strongly suspect it will
be a compromise antenna as opposed to one with a gain, though.


--
73 for now
Buck
N4PGW

skin back the insulation, if any, to be sure

"wb5cys" wrote in message
m...
Considering a wire dipole (or inverted V) does bending the end of a leg
back
and wrapping it around itself electrically shorten the antenna or must it
be
cut in order to change the resonant frequency?

What's a Cobra head?
"Buck" wrote in message
...
On Thu, 16 Jun 2005 09:56:24 -0400, "Fred W4JLE"
wrote:

That being the case, can I just keep folding back a 120 foot insulated
wire
dipole until it is say 5 or 6 foot long and it will still be resonant on
the original frequency?

"Dave" wrote in message
...
if it is insulated wire it must be cut, if its not then it doesn't.
though
you will see some effect of folding it back even with insulated wire it
won't be the same as cutting the wire shorter.

No one said it would be resonant on the SAME frequency, just that
there will be some effect. I have heard about an antenna design for a
shortened dipole using 3-conductor home electrical wire. At one end,
the green is connected to the cobra-head and the black and white wires
are soldered together. At the other end, the black is soldered to the
green. Viola -- a linear loaded dipole!

I haven't tried it, but if it works, you may very well get your
desired frequency with folded wire. I would strongly suspect it will
be a compromise antenna as opposed to one with a gain, though.


--
73 for now
Buck
N4PGW

Henry Kolesnik wrote:
What's a Cobra head?
"Buck" wrote in message
...
On Thu, 16 Jun 2005 09:56:24 -0400, "Fred W4JLE"
wrote:

That being the case, can I just keep folding back a 120 foot insulated
wire
dipole until it is say 5 or 6 foot long and it will still be resonant on
the original frequency?

"Dave" wrote in message
...
if it is insulated wire it must be cut, if its not then it doesn't.
though
you will see some effect of folding it back even with insulated wire it
won't be the same as cutting the wire shorter.

No one said it would be resonant on the SAME frequency, just that
there will be some effect. I have heard about an antenna design for a
shortened dipole using 3-conductor home electrical wire. At one end,
the green is connected to the cobra-head and the black and white wires
are soldered together. At the other end, the black is soldered to the
green. Viola -- a linear loaded dipole!

I haven't tried it, but if it works, you may very well get your
desired frequency with folded wire. I would strongly suspect it will
be a compromise antenna as opposed to one with a gain, though.


--
73 for now
Buck
N4PGW

As I recall it is a commercial name for a center insulator for the
common dipole. It was narrow at the bottom to accept the feed line,
and flared out at the top for connection to the dipole elements. With
the transmission line connected it sorta looked like the head of a
cobra snake. I haven't seen a cobra in person, nor have I saw a cobra
head insulator. I think I would like to keep it that way.
Gary N4AST

On Thu, 16 Jun 2005 21:12:50 GMT, "Henry Kolesnik"
wrote:

What's a Cobra head?


Back in the good-ole-days, a cobra head was a triangle shaped device
that had an SO-239 on one corner and connections for the wires of a
dipole on the other two corners. One went to the center conductor and
the other went to the shield side. Then Baluns became popular and now
instead of cobra heads, most people have baluns. However, at that
time in ham radio, "Cobra head" was a generic term that meant the
piece to connect the wires of a dipole to a piece of coax.


--
73 for now
Buck
N4PGW

On Thu, 16 Jun 2005 17:56:52 -0400, Buck wrote:

On Thu, 16 Jun 2005 21:12:50 GMT, "Henry Kolesnik"
wrote:

What's a Cobra head?


Back in the good-ole-days, a cobra head was a triangle shaped device
that had an SO-239 on one corner and connections for the wires of a
dipole on the other two corners. One went to the center conductor and
the other went to the shield side. Then Baluns became popular and now
instead of cobra heads, most people have baluns. However, at that
time in ham radio, "Cobra head" was a generic term that meant the
piece to connect the wires of a dipole to a piece of coax.

B&W still sells a cobra head center insulator...

http://www.bwantennas.com/pro/support.pro.htm

I'm trying to figure out how they get $179 for it.

bob
k5qwg

B&W still sells a cobra head center insulator...

http://www.bwantennas.com/pro/support.pro.htm

I'm trying to figure out how they get $179 for it.

bob
k5qwg



Does it come with an antenna?

--
73 for now
Buck
N4PGW