Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old December 7th 07, 08:17 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jan 2007
Posts: 26
Default Quad loop supported by single tower - NEC2 modeling question

Hi,

I am modeling a vertically oriented, vertically polarized loop for
160 meters. The loop will be supported at the top of a 130 foot tall
tower with a 6 foot standoff arm. The Bottom of the loop will be 10
feet from the ground. I was modeling the exact physical layout of the
loop with NEC2 without considering the tower structure in the model
at all.

The tower is Rohn 45G with non-conductive guy wires. Not wanting to
duplicate the exact tower model in NEC2 (by hand), I substituted in
essentially a wire with a diameter of 1 foot, using steel for the
conductor. I am modeling the antenna over 'real ground'. Putting in
this wire next to the antenna had a pretty big impact on the resonance
frequency that NEC2 reported. The pattern is slightly altered as
well.

My question is, 1) Am I taking too much of a shortcut to use a single
wire to represent the tower? I just wanted a *rough* idea if this
tower length (1/4 wavelength on 160) was going to have some impact on
the pattern in the real world. Resonance frequency shifted down in
frequency 35Khz in my model.

I've modeled and built loops that I've installed between trees and the
results have matched NEC2 very well, but I don't know what to make of
the support steel tower in this case - am I overstating its effect the
way I modeled it?

-Scott, WU2X

  #2   Report Post  
Old December 7th 07, 09:34 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 1,374
Default Quad loop supported by single tower - NEC2 modeling question

You've done the right thing. The tower features are a tiny fraction of a
wavelength, so the single wire substitution is fine.

To improve the accuracy of the model, use the equivalent radius of 0.421
foot for a triangular tower with one foot sides. This will likely make a
noticeable difference only if the tower is somewhere in the vicinity of
self resonance.

Roy Lewallen, W7EL

wrote:
Hi,

I am modeling a vertically oriented, vertically polarized loop for
160 meters. The loop will be supported at the top of a 130 foot tall
tower with a 6 foot standoff arm. The Bottom of the loop will be 10
feet from the ground. I was modeling the exact physical layout of the
loop with NEC2 without considering the tower structure in the model
at all.

The tower is Rohn 45G with non-conductive guy wires. Not wanting to
duplicate the exact tower model in NEC2 (by hand), I substituted in
essentially a wire with a diameter of 1 foot, using steel for the
conductor. I am modeling the antenna over 'real ground'. Putting in
this wire next to the antenna had a pretty big impact on the resonance
frequency that NEC2 reported. The pattern is slightly altered as
well.

My question is, 1) Am I taking too much of a shortcut to use a single
wire to represent the tower? I just wanted a *rough* idea if this
tower length (1/4 wavelength on 160) was going to have some impact on
the pattern in the real world. Resonance frequency shifted down in
frequency 35Khz in my model.

I've modeled and built loops that I've installed between trees and the
results have matched NEC2 very well, but I don't know what to make of
the support steel tower in this case - am I overstating its effect the
way I modeled it?

-Scott, WU2X

  #3   Report Post  
Old December 8th 07, 09:16 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jan 2007
Posts: 26
Default Quad loop supported by single tower - NEC2 modeling question

Thanks Roy!

I guess I was confused about the obvious connection the tower base has
to the ground. Will this have any addition affect?

-Scott, WU2X

On Dec 7, 3:34 pm, Roy Lewallen wrote:
You've done the right thing. The tower features are a tiny fraction of a
wavelength, so the single wire substitution is fine.

To improve the accuracy of the model, use the equivalent radius of 0.421
foot for a triangular tower with one foot sides. This will likely make a
noticeable difference only if the tower is somewhere in the vicinity of
self resonance.

Roy Lewallen, W7EL

wrote:
Hi,


I am modeling a vertically oriented, vertically polarized loop for
160 meters. The loop will be supported at the top of a 130 foot tall
tower with a 6 foot standoff arm. The Bottom of the loop will be 10
feet from the ground. I was modeling the exact physical layout of the
loop with NEC2 without considering the tower structure in the model
at all.


The tower is Rohn 45G with non-conductive guy wires. Not wanting to
duplicate the exact tower model in NEC2 (by hand), I substituted in
essentially a wire with a diameter of 1 foot, using steel for the
conductor. I am modeling the antenna over 'real ground'. Putting in
this wire next to the antenna had a pretty big impact on the resonance
frequency that NEC2 reported. The pattern is slightly altered as
well.


My question is, 1) Am I taking too much of a shortcut to use a single
wire to represent the tower? I just wanted a *rough* idea if this
tower length (1/4 wavelength on 160) was going to have some impact on
the pattern in the real world. Resonance frequency shifted down in
frequency 35Khz in my model.


I've modeled and built loops that I've installed between trees and the
results have matched NEC2 very well, but I don't know what to make of
the support steel tower in this case - am I overstating its effect the
way I modeled it?


-Scott, WU2X


Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Modeling the effect of a tower Cecil Moore Antenna 3 March 9th 07 01:40 AM
Dipole vs. Delta loop vs. Quad loop -pratical experience Jim Leder Antenna 9 February 23rd 05 12:37 AM
Muilti band quad with a single loop? tj Antenna 2 July 21st 04 07:24 PM
NEC2 modeling question Jack Twilley Antenna 8 April 10th 04 01:46 AM
Announcement: New Nec2 modeling available - Nec2Go PatW Antenna 0 March 30th 04 07:55 PM


All times are GMT +1. The time now is 08:23 AM.

Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017