loading coils for UHF
 

Hi All,

At 433 MHz UHF, I need to reduce the lenght of the dipole using loading
coils or a better method.

I need to know if there is a antenna program or a method to determine
values and location.

tnx de KJ4UO.

And how much do you wish to shorten it? I know not many amateurs have room
for a full size 13.6" dipole.

wrote in message
oups.com...
Hi All,

At 433 MHz UHF, I need to reduce the lenght of the dipole using loading
coils or a better method.

I need to know if there is a antenna program or a method to determine
values and location.

tnx de KJ4UO.

with maximum shortening by loading coils, it is possible mattel can
fit such an antenna on a doll house!

John

"Fred W4JLE" wrote in message
...
And how much do you wish to shorten it? I know not many amateurs
have room
for a full size 13.6" dipole.

wrote in message
oups.com...
Hi All,

At 433 MHz UHF, I need to reduce the lenght of the dipole using
loading
coils or a better method.

I need to know if there is a antenna program or a method to
determine
values and location.

tnx de KJ4UO.

I would like to make it half-size.

Can I just take the full-size dipole and roll the extra copper into a
coil in the center?

de KJ4UO

If you wind the helical coils with large spacing between turns--pretty
close...

The capacitance across the windings of the coils will be the most
notable effect, and will induce a need to shorten the electrical
length of the element conductors, keeping that capacitance to a
minimum may allow this need to be insignificant. If not, just trim
wire length a bit.

Best might be to set up with a "wand" which can be lengthened or
shortened a bit on each element which is so shortened by a coil.

John

wrote in message
oups.com...
I would like to make it half-size.

Can I just take the full-size dipole and roll the extra copper into
a
coil in the center?

de KJ4UO

Will this be used for receive only or do you plan to transmit on it as well?

wrote in message
oups.com...
I would like to make it half-size.

Can I just take the full-size dipole and roll the extra copper into a
coil in the center?

de KJ4UO

Loading coils do NOT shorten an antenna! They electrically lengthen an
antenna that is already physically too short.

What do you really want to accomplish?

wrote:
Hi All,

At 433 MHz UHF, I need to reduce the lenght of the dipole using loading
coils or a better method.

I need to know if there is a antenna program or a method to determine
values and location.

tnx de KJ4UO.

I think he is "OBVIOUSLY" speaking of a physical shortening.

In that light, not only will your comments be confusing, but also of
no, or even a negative use...

John

"Ham op" wrote in message
...
Loading coils do NOT shorten an antenna! They electrically lengthen
an antenna that is already physically too short.

What do you really want to accomplish?

wrote:
Hi All,

At 433 MHz UHF, I need to reduce the lenght of the dipole using
loading
coils or a better method.

I need to know if there is a antenna program or a method to
determine
values and location.

tnx de KJ4UO.

I would like to make it half-size.

Can I just take the full-size dipole and roll the extra copper into
a
coil in the center?

de KJ4UO

----------------------------------------------------------------
No you can't.

Program ADDALOAD calculates the value of a loading coil to resonate an
antenna wire of given length at any frequency. The location of the
coil as a fraction of length along the antenna wire can be chosen in
advance.

That's if it's possible of course. In some cases a loading capacitor
is needed.

You will need a coil in each half of the dipole.

Download in a few seconds program ADDALOAD from website below and run
immediately.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

wrote:
I would like to make it half-size.

Can I just take the full-size dipole and roll the extra copper into a
coil in the center?

de KJ4UO

Sorry, that doesn't work. A length of stretched out wire doesn't behave
the same when it's wound into a coil. The reason is that the field from
one turn of the coil couples strongly to the other turns, while the
field from a straight wire couples only weakly to the adjacent regions
of straight wire. That's why a coil has more inductance than a straight
wire of the same wire length.

The problem with using a simple program to answer your question is that
at that frequency any coil is likely to be a sizeable fraction of a
wavelength long, and perhaps in diameter and therefore will radiate
substantially. So a lumped inductance won't be a good representation of
the coil. EZNEC's helix creation feature would let you realistically
model any proposed inductor and get an accurate answer. Unfortunately,
the free demo version won't have enough segments to do this. You can get
more information about it at http://eznec.com. You could model some very
simple helical inductors of a turn or two with the demo program to get
an idea of how the program works.

Roy Lewallen, W7EL