NetStumbler.org Forums - View Single Post

dax · 12-15-2002

Q: How do I determine what the thickness of the volume is? Is that a pre-determined measure based on db rating? It seems that a omni would be at least like a dome from left extreme to right extreme, but how tall?

A: You don't measure this in physical units (like feet, meters or kilometers), it is measured in dB. Specifically, the -3db measurement is important, as that is the halfway point in measuring the signal strength.

In order to "see" the pattern, you should look at the manufacturer's diagrams "e" and "h" plane diagrams. This will show the most information.

The signal from an omni doesn't look like a dome, as the signal comes from along the length of the wire. As you move to a point in space where the wire appears head on (a little round dot) the signal drops off to zero, as little or no signal comes off the end of the wire. Hence, you get a donut shape.

A sufficiently sensitive receiver, moving closing around a powerful transmitter's omni, might show a dome pattern, but for most real world RF applications the doughnut pattern is a good working model.

Asked by dax
Answered by Thorn

12-15-2002	#11 (permalink)
dax Registered Member Join Date: Dec 2002 Location: No CA Posts: 3	Re: Omnidirectional Patterns and dB Q: How do I determine what the thickness of the volume is? Is that a pre-determined measure based on db rating? It seems that a omni would be at least like a dome from left extreme to right extreme, but how tall? A: You don't measure this in physical units (like feet, meters or kilometers), it is measured in dB. Specifically, the -3db measurement is important, as that is the halfway point in measuring the signal strength. In order to "see" the pattern, you should look at the manufacturer's diagrams "e" and "h" plane diagrams. This will show the most information. The signal from an omni doesn't look like a dome, as the signal comes from along the length of the wire. As you move to a point in space where the wire appears head on (a little round dot) the signal drops off to zero, as little or no signal comes off the end of the wire. Hence, you get a donut shape. A sufficiently sensitive receiver, moving closing around a powerful transmitter's omni, might show a dome pattern, but for most real world RF applications the doughnut pattern is a good working model. Asked by dax Answered by Thorn __________________ "The Truth Is Out There" Last edited by Thorn : 02-13-2003 at 07:47 AM.