This attempt is virtually similar to a multiband dipole, where 2 or more
band elements are separated by mere inches. Of course, you have to expect
pattern & resonance changes from that and adjust lengths accordingly, but
you'll never overcome the pattern "distortions" on the higher band(s). That
is often ok, tho, depending on what your objectives are.
It may be better to look at alternative designs that I believe perform
better than zepp derivatives: (1) Windoms, esp Carolina Windom, (2) bottom
apex fed delta loops, esp Super Delta Loop. I've found both of these
extremely challenging to model in anything less the the expensive pro
modeling programs based on NEC4, esp the ladder line stub in the Super Delta
Loop.
Stephen W9SK
-----Original Message-----
From: antennaware-bounces@contesting.com
[mailto:antennaware-bounces@contesting.com] On Behalf Of Paul Decker
Sent: Friday, September 11, 2009 7:00 AM
To: Guy Olinger K2AV
Cc: antennaware@contesting.com
Subject: Re: [Antennaware] Multiband antennas
Hi Guy,
That is what I was thinking last night, that because the 20 is the second
harmonic even with the traps, the close proximity of the 40 will cause
problems. Separation of the antenna's seem to make a big difference in
the model, even only by 5 feet or so seems to make things work out much
better, even without traps or switching.
73,
Paul (KG7HF)
----- Original Message -----
From: "Guy Olinger K2AV" < olinger @ bellsouth .net>
To: "Paul Decker" <kg7hf@comcast.net>
Cc: antennaware @contesting.com
Sent: Friday, September 11, 2009 9:26:10 AM GMT -05:00 US/Canada Eastern
Subject: Re: [ Antennaware ] Multiband antennas
The length on 40 makes it excitable on 20 meters, simply due to the
proximity, with or without the feedline attached. Putting EDZ's for 20 and
40 in proximity probably won't work in the ordinary sense. One will have to
model it as a combo even if you used relays to isolate feedline . Either
half of the 40 is fully excitable on 20.
You may be able to feed the 40 only with the 20 length moderating the
pattern of the longer 40 wire on 20 meters. This would be something you
would have to model into submission and then try out. Some have used 450
window line for the zepp parts in designs like this.
This "open cell" approach for harmonically related frequencies is used on
some of Force12's triband yagi's .
73, Guy
On Thu, Sep 10, 2009 at 8:20 PM, Paul Decker <kg7hf@comcast.net> wrote:
>
>
> I'm trying to design an antenna, actually combine two already designed
antennas to use a common feeder. The 40 meter antenna would be fed from a
short 6" length of feedline from the 20 meter antenna.
>
>
>
> I have a 20 and 40 meter extended double zepp , both fed with 600 Ohm open
wire line. When I combine the antenna's together, of course, it changes
the characteristics. The combined antenna models fine for 40 meters, but
changes wildly for 20. I was thinking that adding a low pass filter or
"trap" to the feedline which feeds the 40 meter antenna, the idea being to
cut it out of the picture.
>
>
>
> So the modeling question is this, how do i model a trap, I thought it
would simply be a parallel load with some RLC value, but this doesn't appear
to work correctly for me.
>
>
>
> My second question is, does anyone have any ideas on how to make this
work?
>
>
> The antenna's are modeled like this:
>
> Wires:
>
> 1 W3E1 -3, 0, 780 -528, 0,
780
> #14 200 1 0
> 2 W4E1 3, 0, 780 528, 0,
780
> #14 200 1 0
> 3 W6E1 -3, 0, 780 W5E1 -3, 0,
125
> #14 50 1 0
> 4 W7E1 3, 0, 780 W5E2 3, 0,
125
> #14 50 1 0
> 5 W3E2 -3, 0, 125 W4E2 3, 0,
125
> #14 1 1 0
> 6 W1E1 -3, 0, 780 W8E1 -3, 0,
786
> #14 10 1 0
> 7 W2E1 3, 0, 780 W9E1 3, 0,
786
> #14 10 1 0
> 8 W6E2 -3, 0, 786 -1056, 0,
786
> #14 200 1 0
> 9 W7E2 3, 0, 786 1056, 0,
786
> #14 200 1 0
>
>
>
>
> Loads:
>
> 1 8 33.00 32.75 66 Short Short
> 12 0 Ser
> 2 9 33.00 32.75 66 Short Short
> 12 0 Ser
> 3 1 33.00 32.75 66 Short Short
> 6 0 Ser
> 4 2 33.00 32.75 66 Short Short
> 6 0 Ser
> 5 6 0.00 5.00 1 150 3.5
> 152 0 Trap
> 6 7 0.00 5.00 1 150 3.5
> 152 0 Trap
>
>
>
>
> Source:
>
> 1 5 50.00 50.00 1 1 0
> I
>
>
>
>
>
>
>
>
> By the way, individually, these antennas perform great in real world
tests!
>
>
>
>
>
> 73,
> Paul (KG7HF)
> _______________________________________________
> Antennaware mailing list
> Antennaware @contesting.com
> http ://lists.contesting.com/mailman/ listinfo / antennaware
>
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