[Elecraft] Re: More antenna problems

[George, W5YR]

I regret that in my Socratic approach. I failed to make the point I was
trying to make. Specifically that while vertical antennas may have a low
takeoff angle their gain is usually less than that of an isotropic antenna.

For example, look at "vert1.ez" in EZNEC and you find that its gain is -0.04
dB max at an elevation angle of about 25 degrees. Similarly, if you look at
"bydipole.ez" on 40 meters you find that although the elevation angle for a
dipole height of 30 ft is near 90 degrees, the gain is over 7 dBi. Raise the
dipole to 67 ft as Earl points out and the gain increases slightly but the
takeoff angle declines to about 30 degrees and the azimuth pattern begins to
form.

So, Earl's points are well made: high dipoles if low-angle radiation is
desired with gain over isotropic or vertical antennas performing essentially
as isotropics but with a low takeoff angle. To me, the trade-off is that if
you take the wire invested in the vertical and the radial field and can
manage to get it up in the air high enough, you obtain significant gain over
isotropic, a low takeoff angle and some degree of azimuthal pattern - which
may or may not be advantageous depending upon the orientation of the antenna
supports.

73, George W5YR
Fairview, TX
w5yr at att.net
http://www.w5yr.com




----- Original Message ----- 
From: "Earl W Cunningham" <k6se at juno.com>
To: <w5yr at att.net>; <pbuckley at woh.rr.com>; <elecraft at mailman.qth.net>
Sent: Wednesday, July 28, 2004 12:01 PM
Subject: Re: [Elecraft] Re: More antenna problems


> George,  W5YR writes:
>
> "Parker, what did you think of the EZNEC gain predictions for verticals?
> Compared to wire dipoles at a modest height?"
> ==========
> The free space gain of a vertical is about the same as that of a dipole
> (2.14 dBi).  However, over real ground the horizontal antenna benefits by
> far field ground reflection.  This is borne out in EZNEC.
>
> Remember that a vertical's gain is concentrated at the low angles that
> are good for DXing, while the horizontal antenna must be relatively high
> (at least 0.5 wavelengths) to have a reasonably low angle of radiation..
>
> As far as noise goes, the dipole has a better receive S/N ratio than a
> vertical simply because it has directivity, while the vertical is
> omnidirectional.  Also, because of its low angle radiation, the vertical
> "hears" man made noises better (which are generated close to the ground
> and therefore arrive at a low angle).
>
> 73, de Earl, K6SE