Trap dipole
 

Nate Bargmann wrote:
On Sun, 07 Jan 2007 21:47:05 -0800, Richard Clark wrote:
I don't follow the logic of this at all. Are you expecting the trap
to cut off all frequencies above 27.5 MHz?

This is what W8JI's site hints at. Is he wrong, or am I misunderstanding
him?

Unlike low pass filters, traps do not have a low impedance
at lower frequencies and a higher impedance at high frequencies.
The impedance plot Vs frequency is akin to a bell shaped
curve with the maximum impedance at resonance.
--
73, Cecil http://www.w5dxp.com

Trap dipole
 

On Mon, 08 Jan 2007 20:37:23 -0600, Nate Bargmann
wrote:

I don't follow the logic of this at all. Are you expecting the trap
to cut off all frequencies above 27.5 MHz?

This is what W8JI's site hints at. Is he wrong, or am I misunderstanding
him?

Hi Nate,

Simply examine the transfer characteristics of any series or parallel,
resonant circuit. It has a peak, not a band-reject characteristic,
that is why it is called resonant. You resonate traps at one distinct
frequency where the roll-off may serve the purpose over a slightly
wider region. A 10M trap does not "remove" the surplus wire for all
frequencies above, say, 28.4 MHz, and probably doesn't work for the FM
portion of the band.

73's
Richard Clark, KB7QHC

Trap dipole
 

On Mon, 08 Jan 2007 23:45:32 -0800, Richard Clark wrote:

Hi Nate,

Simply examine the transfer characteristics of any series or parallel,
resonant circuit. It has a peak, not a band-reject characteristic,
that is why it is called resonant. You resonate traps at one distinct
frequency where the roll-off may serve the purpose over a slightly
wider region. A 10M trap does not "remove" the surplus wire for all
frequencies above, say, 28.4 MHz, and probably doesn't work for the FM
portion of the band.

Honestly, Richard, your explanation was always my assumption and
understanding. W8JI seems to be saying that by resonating them lower the
benefit was lower loss. Now, I believe he was examining the 40m traps
used in W8NX's antenna featured in various issues of QST.

I think I ought to construct the durned thing and not worry about the
minutia. ;-)

- Nate

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."

Trap dipole
 

On Tue, 09 Jan 2007 03:10:28 +0000, Cecil Moore wrote:

Nate Bargmann wrote:
On Sun, 07 Jan 2007 21:47:05 -0800, Richard Clark wrote:
I don't follow the logic of this at all. Are you expecting the trap
to cut off all frequencies above 27.5 MHz?

This is what W8JI's site hints at. Is he wrong, or am I misunderstanding
him?

Unlike low pass filters, traps do not have a low impedance
at lower frequencies and a higher impedance at high frequencies.
The impedance plot Vs frequency is akin to a bell shaped
curve with the maximum impedance at resonance.

Right. That has always been my understanding. I think W8JI was strictly
looking at loss. His page has little commentary as I understand that what
is there were slides at a Dayton forum.

- Nate

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."

Trap dipole
 

Nate Bargmann wrote:
I think W8JI was strictly
looking at loss. His page has little commentary as I understand that what
is there were slides at a Dayton forum.

A trap would naturally have higher losses at
its resonant frequency because that's where the
internal circulating currents are the highest.
Detuning the trap would reduce trap losses.
Removing the trap would reduce trap losses. :-)
--
73, Cecil http://www.w5dxp.com

Trap dipole
 

On Tue, 09 Jan 2007 20:41:04 -0600, Nate Bargmann
wrote:

I think I ought to construct the durned thing and not worry about the
minutia. ;-)

Hi Nate,

That idea has a lot of traction.

73's
Richard Clark, KB7QHC