[WARC] antenna modeling result.

[Clare Jarvis]

On Monday 21 May 2007 22:59, Leslie Hittner wrote:
> Clare,
>
> Sounding more interesting every time you discuss it. I have some
> questions:
>
> What is the half-power beam width on 80, 40, and 20 meters (main
> lobes)?

70 degrees at 14.25 MHz
54 degrees at 7.15 MHz
121 degrees at 3.7 MHz
>
> What are the reactive components of the impedance on each of
> those bands?

85.64 -j5.107 ohms at 14.25 MHz
140 + j1362 ohms at 7.16 MHz
7898 - J19040 oms at 3.74 MHz

SWR minimums occurr at
14.24, 12.36, 10.42, 8.56, 6.68, 4.76 MHz
amazingly at equal spacing.   


>
> Is that 250 feet on a leg?

258.657 Feet each leg with a slope from 30 feet elevation to 10 feet 
elevation.  Horizontal distance of 257.883 feet.

>
> How does the gain/beam width of thge main lobe vary with the
> angle between the legs?
I have been using the predicted max gain angle from the antenna book for 3+ 
wave lengths.   The dimensions are for a 20 meter antenna.  The patterns are 
not clean but suprisingly not all that dirty either.

>
> How does the impedance vary on, say, 80 meters with a change in
> angle?

I am not temped to play too much with that considering the chart in the 
antenna book.  What playing I have done indicates that patterns are really 
strange when straying from the chart.   I tried 20 and 45 degree angles and 
they had strange patterns but a good strong center lobe.   

>
> -Les
>
> ----- Original Message -----
> From: "Clare Jarvis" <clarej at hbci.com>
> To: "Winona Amateur Radio Club general discussion"
> <warc at lists.w0ne.org>
> Sent: Monday, May 21, 2007 10:08 PM
> Subject: [WARC] antenna modeling result.
>
> > I have modeled a v-beam that uses aprox 500 feet of wire but
>
> has 7.93dBd of
>
> > gain at 14.22 MHz.   The front to back ratio is 1:1 and the
>
> take off angel is
>
> > 20 degrees.   If anybody is interested I can show nice plots
>
> of gains and
>
> > take-off angles.
> >
> > BTW this model has significant gain on both 40 and 80 meters
>
> but is quite
>
> > reactive.  If someone would like to work on how to feed it on
>
> these other
>
> > bands then we should be able to lighjt up both the left and
>
> right coast on
>
> > three bands.   This antenna should be easy to erect.
> >
> > 73 Clare
> > _______________________________________________
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>
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