I have been looking at the properties of a cage or fat dipole. This is
efficient and has a wide bandwidth. But what happens if a trap is added to
then with an extension to cover an additional lower band. Will the high Q
trap significantly reduce the efectiveness of the cage dipole in efficiency
and bandwidth? I was thinking in terms of a cage dipole-trap-cage
extension. Any thoughts?

73 de Dick G4BBH

On Mon, 15 Jan 2007 21:26:48 -0000, "ferrymanr"
wrote:

I have been looking at the properties of a cage or fat dipole. This is
efficient and has a wide bandwidth. But what happens if a trap is added

Hi Dick,

It would seem to be a contradiction in sizes (the coil and cap have to
be much smaller), but then when I think of cage antennas, I see:
http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm

The point of the cage is to not need adornments.

73's
Richard Clark, KB7QHC

"
I have been looking at the properties of a cage or fat dipole. This is
efficient and has a wide bandwidth. But what happens if a trap is added

Hi Dick,

It would seem to be a contradiction in sizes (the coil and cap have to
be much smaller), but then when I think of cage antennas, I see:
http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm

The point of the cage is to not need adornments.

73's
Richard Clark, KB7QHC

Since the elements of a cage dipole usually come to a point at both ends
(the feed and the far end for attachment of a support) I can see no problem
in physically adding a trap.

Above the trap cut-off frequency the extensions will have little effect on
the performance. At lower frequencies where you will effectively have a
dipole element with a fat portion and then a thinner bit at the end , it
should work ok but you may need some modelling to see exactly what happens
to the bandwidth.

73
Jeff

"Jeff" wrote in message
. com...

Since the elements of a cage dipole usually come to a point at both ends
(the feed and the far end for attachment of a support) I can see no
problem in physically adding a trap.

Above the trap cut-off frequency the extensions will have little effect on
the performance. At lower frequencies where you will effectively have a
dipole element with a fat portion and then a thinner bit at the end , it
should work ok but you may need some modelling to see exactly what happens
to the bandwidth.

73
Jeff
I have modelled it in MMANA (my cage is similar to 'fat dipole2.maa') and it
looks feasible. The cage resonant frequency drops a tad but the extension
after the trap, modelled with a 3mm wire, does resonant nicely. This allows
me to add an extra band somewhat below the normal low limit of the cage
dipole. My modelling still shows a reasonable bandwidth for the main cage
dipole but I suspect the trap will have some complex effects above and below
resonance. I will have to try it to see how much it affects it will have.
It will be easy to clip a trap to each end of the main dipole for the tests.

73 de Dick G4BBH