[HCARC] Inverted L Antenna

galeheise at windstream.net galeheise at windstream.net
Sun Feb 16 13:02:23 EST 2014 

Great explanation Dale!

-----Original Message----- 
From: Dale Gaudier
Sent: Sunday, February 16, 2014 9:55 AM
To: 'Gary J - N5BAA' ; hcarc at mailman.qth.net
Subject: Re: [HCARC] Inverted L Antenna

Gary:

Gale and Kerry have both given you good information. Given the rocky terrain
around here (= poor ground conductivity) it's hard to get a short vertical
to radiate efficiently. Lots of radials can help. Elevated radials might
also be an alternative. Check out the series of articles by N6LF on
grounding and radials for vertical antennas (Google "antennasbyn6lf").

Soil conductivity can vary from location to location. I suspect it's pretty
bad where my tower sits on the top of exposed solid limestone on the 90 ft.
hill behind my shack. It's probably a bit better down at the shack where
there is at least a few feet of alluvial soil. One of the things I will
eventually get around to doing is measuring the soil conductivity near where
I have my antennas so I can have a more accurate number for modeling the
ground using EZNEC. N6LF describes a simple method to do this in one of his
articles.

The thing that counts for DX is having a low angle of radiation near the
horizon. Generally a takeoff angle of 10-30 degrees is good - the exact
angle depends on propagation and the distance you want to cover. The takeoff
angle is a combination of the direct wave and ground reflected wave.
Predicting how these will behave and interact can be difficult when you have
nearby hills and will vary somewhat depending on frequency. At longer
wavelengths (e.g. 160m) the typical Hill Country hill will have relatively
minor influence on a radio wave. Because the rock is not very conductive,
there will be little or no reflection or refraction and only minor
absorption of the wave. The hills are short compared to the long wavelength
and so are relatively "transparent" at these lower frequencies.

The ARRL Antenna book comes with a CD with a program called HF Terrain
Assessment that allows you to take US Geological Survey map information for
your location and calculate the behavior (e.g. takeoff angle) of various
types of horizontally polarized antennas (e.g. dipoles and Yagis) at chosen
heights and frequencies. You'll need to have an idea of what the soil
conductivity in the area is, too, as this influences the reflected wave and,
hence, the takeoff angle. Something to play around with if you're really
interested in seeing the effect of siting of dipoles and Yagis you are
thinking of installing. I didn't see an option in the program for doing
similar calculations for vertical antennas, though.

73,

Dale



-----Original Message-----
From: hcarc-bounces at mailman.qth.net [mailto:hcarc-bounces at mailman.qth.net]
On Behalf Of Gary J - N5BAA
Sent: Saturday, February 15, 2014 9:17 PM
To: Dale Gaudier; hcarc at mailman.qth.net
Subject: Re: [HCARC] Inverted L Antenna

If playing around on the hillside gains me NADA, I won't waste the coax or
ditching effort getting me there!!!  Doesn't the take off angle change on a
hillside???  Of course I have tall hills several miles away directly west
across from the hillside.  Lowered take off may just run into the hills
across the valley.

73,


Gary J
N5BAA
HCARC Secretary 2013/14

-----Original Message----- 
From: Dale Gaudier
Sent: Saturday, February 15, 2014 8:57 PM
To: 'Gary J - N5BAA' ; hcarc at mailman.qth.net
Subject: RE: [HCARC] Inverted L Antenna

Gary:

According to the ARRL Antenna Book, you'll get some slight directionality in
the direction of the sloping wire. The vertical part of the antenna will
give you vertically polarized radiation, which is good for low angles of
radiation and DX. The sloping part will have a mix of vertically and
horizontally polarized radiation.

73,

Dale - K4DG

-----Original Message-----
From: hcarc-bounces at mailman.qth.net [mailto:hcarc-bounces at mailman.qth.net]
On Behalf Of Gary J - N5BAA
Sent: Saturday, February 15, 2014 8:07 PM
To: hcarc at mailman.qth.net
Subject: [HCARC] Inverted L Antenna

What happens, if anything, to an inverted L (80 or 160 meters) if the
vertical section is right on the edge of a hill approx 50 feet up and the
wire runs downhill to a support approx 50 feet high at the bottom of the
hill??  Does the slope make it at all directional??

Gary J
N5BAA
HCARC Secretary 2013/14
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