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
>
_______________________________________________
Antennaware mailing list
Antennaware@contesting.com
http://lists.contesting.com/mailman/listinfo/antennaware
|