• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
Part15

Part15

License Free, legal, low-power radio broadcasting

  • About Us
  • Forums
  • Resources
  • Members
  • Contact Us
  • Log In
Forums
Main Category
temp
A dimwit trying to ...
 
Notifications
Clear all

A dimwit trying to grasp Ermi Roos dipole..

 
temp
Last Post by Anonymous 9 years ago
4 Posts
2 Users
0 Reactions
551 Views
RSS
RichPowers
 RichPowers
(@richpowers)
Posts: 3358
Famed Member Registered
Topic starter
 

I'm trying to grasp exactly what Ermi Roos was sayinging in the following post from back in 2008. It's bugging the crap out of me..
It's dancing right there in front of my eyes but I just have not been able to grab it.. Can anyone interprit this in toddler terms?
(This is copied from http://www.part15.us/blogs/ermi-roos/earliest-radio?page=1 beginning at the end of Post 42 and then continues in Post 44)

==============================================

I will next show that the signal does not have to be as low as the Section 15.209 range if a ground lead is not used. A 3 m dipole remote from ground has an input impedance of about .05 - j6000 ohms. It would not be unreasonable for me to assume the same 25 ohms loss resistance that I assumed for the monopole over ground, because, although the loading coil inductance has to be doubled, there is no ground loss. The radiated power is 50 uW. The field strength at one radianlength is 1.69 mV/m, taking into account the lower gain of a dipole compared to a monopole. If a vertical dipole is not remote from ground, the radiation resistance increases, increasing to .1 ohms very close to ground. An elevated vertical dipole launches both a skywave and a groundwave. If the lower arm of the dipole has a ground lead, the radiation resistance goes up to .2 ohms (excluding the loss resistance which now includes ground resistance), and the antenna reactance goes down to around the midpoint of 3000 and 6000 ohms. Only groundwave is launched. A grounded 3 m dipole gives better performance than a 3 m monopole above ground.

What I have illustrated here is that a Part 15.219 transmitter produces radiation down at the Part 15.209 levels, as the FCC originally intended, only if it is specifically designed for poor efficiency, such as transmitters intended only for operation inside of a home. Part 15 AM transmitters tend to work very well in the home because of the high near field ar very short distances. A ground lead, even if it is not intended to be radiating, helps efficiency tremendously. However, even if a ground lead is not used, 15.219 transmitters can produce much higher field strengths than the 15.209 limits.

A vertical dipole not remote from the earth, but elevated above ground far enough so that its input impedance is nearly the free-space value, launches a skywave that eventually follows the surface of the earth. This wave is similar to, but not exactly the same as, a groundwave, so it is called a quasi-groundwave. At a distant point, the wavefront of the quasi-groundwave is the combination of two different waves. One wave is reflected, and the other is direct. A small vertical monopole above ground, and a short grounded dipole, both generate only groundwaves. At a distant point, only a single wave is present.

This distinction between the quasi-groundwave and the groundwave makes a difference in the strength of the signal received at a distant point because of either constructive or destructive interference between the two vaves of the quasi-groundwave. No interference occurs due to a pure groundwave, because only a single wave is present.

Edit: Maybe there is a confusion about the meaning of the words "skywave" and "groundwave." A skywave originates from an elevated direction, and it can be reflected from the ground plane. A ground wave cannot be reflected from a perfect, flat, ground plane because the wavefront propagates along the surface of the ground plane. The groundwave can be reflected from an elevated reflector, like the ionosphere. The reflected groundwave becomes a skywave.

===================================================

 

The above edit is his not mine


 
Posted : 04/01/2017 9:54 am
 Anonymous
(@Anonymous)
Posts: 0
 

It reads to me that the RF is being fed to a vertical system above ground, and there's a top section of antenna, a split where the RF is applied, and the bottom part of the antenna goes to the ground and connects to it. With the RF fed to the split, the antenna acts like a dipole, even with one side grounded or unequal lengths on each side.

I wish the site had more people like that these days, thinking about theories and possibilities rather than rules and restrictions and all the "new woes". I'm a nerd for that kind of tech stuff, and the comparison to traveler's service stations that have a hundred times the ERP of what we're supposed to have, from the original article.


 
Posted : 05/01/2017 1:14 pm
 Anonymous
(@Anonymous)
Posts: 0
 

I found the key!

I removed all the text that confused me, and what remained revealed the answers…

============================================================

I will next show that the signal does not have to be as low as the Section 15.209 range if a ground lead is not used. A grounded 3 m dipole gives better performance than a 3 m monopole above ground.

What I have illustrated here is that a Part 15.219 transmitter produces radiation down at the Part 15.209 levels, as the FCC originally intended, only if it is specifically designed for poor efficiency, such as transmitters intended only for operation inside of a home.

A ground lead, even if it is not intended to be radiating, helps efficiency tremendously. However, even if a ground lead is not used, 15.219 transmitters can produce much higher field strengths than the 15.209 limits.

=============================================================

Ok.. So, A grounded transmitter works better than one without ground, and 15.219 produce higher field strength than 15.209

Well I already knew that.

At least the quest was fun.


 
Posted : 05/01/2017 11:38 pm
 Anonymous
(@Anonymous)
Posts: 0
 

I miss what Ermi brought to the table.


 
Posted : 06/01/2017 10:28 am
Forum Jump:
  Previous Topic
Next Topic  
Share:
Forum Information
Recent Posts
Unread Posts
Tags
  • 13 Forums
  • 7,740 Topics
  • 63.5 K Posts
  • 35 Online
  • 2,249 Members
Our newest member: electronic
Latest Post: 7 Beatles Misheard Lyrics
Forum Icons: Forum contains no unread posts Forum contains unread posts
Topic Icons: Not Replied Replied Active Hot Sticky Unapproved Solved Private Closed

Primary Sidebar

Online Members

 No online members at the moment

Recent Posts

  • Mark

    RE: 7 Beatles Misheard Lyrics

    Many songs have I heard something other than the actual...

    By Mark , 1 day ago

  • Mark

    RE: 7 Beatles Misheard Lyrics

    Have you heard this?

    By Mark , 1 day ago

  • RichPowers

    Unique AM Transmitter

    Here one I've not seen before. they're $69.50 on eBay, ...

    By RichPowers , 2 days ago

  • RichPowers

    7 Beatles Misheard Lyrics

    As far as I'm concerned this article is ridiculous, I d...

    By RichPowers , 2 days ago

  • Mark

    RE: Newly Discovered Robert Johnson in Stunning Clarity

    @richpowers Sounds good.

    By Mark , 2 days ago

Recent Topics

  • RichPowers

    Unique AM Transmitter

    By RichPowers 2 days ago

  • RichPowers

    7 Beatles Misheard Lyrics

    By RichPowers 2 days ago

  • RichPowers

    Public Domain Feature Films about Radio

    By RichPowers 3 days ago

  • RichPowers

    Speed Limit 17.3mph

    By RichPowers 5 days ago

  • ArtisanRadio

    Artisan Radio Pivots Again

    By ArtisanRadio 5 days ago

Topic Tags

  • Carl Blare3
  • KDX RADIO3
  • WINDOZE3
  • Transmitter2
  • Radio Phvern2
  • station upgrade2
  • archive.org2
  • playlist2
  • Zara Radio2
  • Carrier Current1
View all tags (74)

Copyright © 2026 · Part15.org · Log in

‹›×

    ‹›×