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Author Topic: Dipole Questions!!!!  (Read 1010 times)
KB3Z
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Posts: 41




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« on: March 13, 2013, 04:54:32 AM »

Good Morning, this is Mark, KB3Z.  I have a perhaps stupid question about the direction of radiation on my G5RV. I have the antenna mounted as follows. The one end is attached to my tower and the other end is mounted at the other end of my yard. More or less the ends are pointing north to south. Now, comes the stupid question. Which direction is my signal going? Is it radiating north to south or is it radiating east to west. The reason I am asking this is because I would like to mount a new dipole and would like to have a greater presence on 40 and 80 for Europe.  Any help would be much appreciated. Oh, and I live about 35 miles northwest of Philadelphia. Thanks!!!  Mark KB3Z
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AA4PB
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Posts: 13032




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« Reply #1 on: March 13, 2013, 05:08:44 AM »

On the band where a dipole is 1/2 wavelength long (20M for the G5RV) the maximum signal will be off the sides of the antenna provided that it is located high enough above ground. Other bands will have multiple lobes so you might as well just consider it omni directional. On 80M and 40M it is probably so close to the ground (in terms of wavelength) that the take off angle is high and it is pretty omni-directional.

The bottom line is that I wouldn't worry too much about the direction it is installed for 40M and especially for 80M.
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KR4TH
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Posts: 47




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« Reply #2 on: March 13, 2013, 05:14:18 AM »

if the ends are pointing north and south the antenna lobes will be east and west on 40 meters if it is 65 feet high, on 20 meters it will be multilobe, do you have an antenna book to look at antenna patterns based on antenna height?  It will show all the patterns for length of antenna and height based on wavelength  If the antenna is 20 or 30 ft high directions of radiation on 40 or 80 won't make any difference the pattern will omni directional and the take off angle will be up

wire antennas provide a great lab for theory
73
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K5LXP
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« Reply #3 on: March 13, 2013, 06:02:11 AM »

On the band where a dipole is 1/2 wavelength long (20M for the G5RV) the maximum signal will be off the sides of the antenna

Except, that on 20M a G5RV is three half waves long.  The dominant lobes of a N-S oriented G5RV are NE, SE, SW and NW.


Quote
The bottom line is that I wouldn't worry too much about the direction it is installed for 40M and especially for 80M.

Even at only 30 feet up a G5RV has quite dominant broadside radiation on 40 and noticeably so on 80.  Enough that it would matter to me anyway.


Mark K5LXP
Albuquerque, NM
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KB3Z
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Posts: 41




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« Reply #4 on: March 13, 2013, 09:04:13 AM »

I'm sorry that I didn't specify that the antenna is up about 35 to 40 feet.  I use it primarily for 60, 40 and 80 meters. Thanks for all the help so far!!!  Mark KB3Z
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W5DXP
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« Reply #5 on: March 13, 2013, 09:15:26 AM »

Which direction is my signal going?

Depends upon the band. EZNEC says the SWR on the G5RV coax will be about 23:1 on 60m so don't expect a lot from that band. Here's some N/S oriented G5RV radiation patterns that I generated in 1997 when I was living in Arizona. Click on the band to see those radiation patterns.

http://www.midtel.net/~pmam/g5rv.htm




« Last Edit: March 13, 2013, 09:20:06 AM by W5DXP » Logged
KB3Z
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Posts: 41




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« Reply #6 on: March 13, 2013, 09:28:57 AM »

Thanks Guys!!! Now what I am looking to do is install a new antenna that will be for 10 through 160 meters.  I would like to get it up about 45 or so feet high on all ends. But, what I am going to do is install the center of the dipole on one support.  And then have one leg going out from there and the other leg going out also.  It would more or less look like a "V" type configuration. I know this will work but I guess that will really complicate matters when it comes to the radiation pattern of the antenna.  If it is going to be omni-directional then so be it.  Mark KB3Z
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