Are these antennas any good?

Clyde Vargus2 · 10-15-2004

http://cgi.ebay.com/ws/eBayISAPI.dll...e=STRK:MEWA:IT

and

http://cgi.ebay.com/ws/eBayISAPI.dll...e=STRK:MEWA:IT

With the kind of cable they have, 7 decibels gets knocked down to (how much?) before it gets to the computer?

beakmyn · 10-16-2004

The cable rg-316 has a loss of 0.4 dB/foot = 2.7dB for 6.5 feet
rg-174 2.8 dB for 6.5 feet
Yes, the antennas will work but they're lossy, cheap and lack a ground plane. They're worth bout $12.00-$15.00 IMHO: You'd be happier with the fab-corp 5dB. I love mine.

Clyde Vargus2 · 10-16-2004

More questions:

1. What is a ground plane - size and shape?
2. How much does the fab corp 5 decibel unit cost (I'll look on eBay)?
3. If I get one, I'll also get an Orinoco Gold Classic card, so it'd have to be able to plug right into it. With no fancy adapters or anything.

4. I've seen the pictures of the shape of the radiated signal from low and high debical antennas. The high decibel units have a much flatter pattern. It seems obvious to me that it would remain the same, but will a 7 db antenna have the same pattern of radiated signal even though the cable loses some of its power? In others words it would NOT have the radiated signal pattern of a 4.3 Db antenna if the 7 Db antenna had a cable that lost 2.7 Db on its way to the card and computer?

beakmyn · 10-16-2004

Quote:

Originally Posted by Clyde Vargus2

More questions:

1. What is a ground plane - size and shape?

Ground plane is the small metal disc that is on the bottom of the antenna. Not the base. Definition from wikipedia
"a ground plane is an electrically conductive surface that serves as the near-field reflection point for an antenna, or as a reference ground in a circuit."

The antenna you listed doesn't have one so it must be mounted to a metallic surface, such as a car roof. The car roof then becomes the ground plane.

Quote:

2. How much does the fab corp 5 decibel unit cost (I'll look on eBay)?

If you mention the 'NetStumbler' rebate, about $50.00

Quote:

3. If I get one, I'll also get an Orinoco Gold Classic card, so it'd have to be able to plug right into it. With no fancy adapters or anything.

If you buy the Fab-Corp you'll also need the "12 inch ORiNOCO/Avaya to N-Male Pigtail". You don't want to have the Orinoco connector on the antenna cable. Because, the connector is very small and can be easily broken if overstressed. There's numerous posts on the design of the connector and it essentially comes down to the fact that the connector wasn't designed to be inserted and removed multiple times. See my setup and how to overcome this 'problem'. Back to reason why you want the pigtail, It's relatively inexpensive and if you do break the connector, you need only buy a new pigtail not a whole new antenna. Trust me you don't want to have to try to put one of those tiny connectors on a cable yourself.

Quote:

4. I've seen the pictures of the shape of the radiated signal from low and high debical antennas. The high decibel units have a much flatter pattern. It seems obvious to me that it would remain the same, but will a 7 db antenna have the same pattern of radiated signal even though the cable loses some of its power? In others words it would NOT have the radiated signal pattern of a 4.3 Db antenna if the 7 Db antenna had a cable that lost 2.7 Db on its way to the card and computer?

I believe so but the experts may chime in, and there is a recent discussion on this, along with some simple drawings. Basically with an omni the higher the dB (gain), the flatter the pattern, as you mentioned, but also the antenna becomes more directional as the radiation pattern is narrower. You don't neccesarily want this when wardriving.

Thorn · 10-16-2004

Quote:

Originally Posted by Clyde Vargus2

1. What is a ground plane - size and shape?

http://glossary.its.bldrdoc.gov/fs-1...-017/_2499.htm

Usually, we want the last definition: "a specially designed artificial surface" which is built-in to the antenna assembly and specifically designed for it. The cheap antennae like the 7dBi units lack this, and REQUIRE the use of a vehicle roof or other metallic surface to function properly (second definition.) Typically, 1m^2 is the recommended minimum for these units.

Quote:

Originally Posted by Clyde Vargus2

2. How much does the fab corp 5 decibel unit cost (I'll look on eBay)?

$59.00

Quote:

Originally Posted by Clyde Vargus2

3. If I get one, I'll also get an Orinoco Gold Classic card, so it'd have to be able to plug right into it. With no fancy adapters or anything.

You'll still need a pigtail.

Quote:

Originally Posted by Clyde Vargus2

4. I've seen the pictures of the shape of the radiated signal from low and high debical antennas. The high decibel units have a much flatter pattern. It seems obvious to me that it would remain the same, but will a 7 db antenna have the same pattern of radiated signal even though the cable loses some of its power? In others words it would NOT have the radiated signal pattern of a 4.3 Db antenna if the 7 Db antenna had a cable that lost 2.7 Db on its way to the card and computer?

The pattern remains the same; i.e. flatter, and less spherical. The loss would just make the overall pattern smaller in diameter.

Thorn · 10-16-2004

Quote:

Originally Posted by beakmyn

... but also the antenna becomes more directional as the radiation pattern is narrower.

Not exactly. Make sure you don't confuse gain in a directional with gain in an omni. While they are the same application of math, the results are far different.

*As a directional antenna increases in gain, the pattern narrows from a broad, shallow cone to that of a very slender beam.

*As the gain increase in a omni-directional, it goes from spherical (in theory) to a flat doughnut, to flattened like a dinner plate. There are some diagrams in the Antenna FAQ which illustrate this concept.

beakmyn · 10-16-2004

Donut Theory not be confused with the episode of The Simpons where Homer tells Hawking about his Donut shape Universe theory. Has some good pictures.

My antenna theory is a bit rusty, but two things still hold true.
1. You get what you pay for.
2. The 5db omni from Fab-Corp is worth the money

Clyde Vargus2 · 10-17-2004

Okay, here's a new question. Range with certain antenna setups.

Assuming a standard set of conditions, like one wall of a house and open air space into the back yard / front yard / outdoors in general after that, how far from an AP can you be and still detect it with:

1. Just an Orinoco gold classic card (the only card I'd want to get, based on what I've read about them).

2. An Orinoco card and the cheap 7 Db antenna I found.

3. An Orinoco card and the better 5 Db antenna mentioned in this topic.

What's the Db rating of the Orinoco antenna alone? I tried to find it, but nothing I saw stated it specifically as far as I could tell. I think it's 2 or 2.2 Db?

If I got the cheap 7 Db unit, could I cut out a circle of sheet metal and put it at the base of the antenna, or is it wired into the unit somehow?

I'm just cheap, that's why I ask this.

Thorn · 10-18-2004

Quote:

Originally Posted by Clyde Vargus2

Okay, here's a new question. Range with certain antenna setups.

Assuming a standard set of conditions, like one wall of a house and open air space into the back yard / front yard / outdoors in general after that, how far from an AP can you be and still detect it with:

1. Just an Orinoco gold classic card (the only card I'd want to get, based on what I've read about them).

2. An Orinoco card and the cheap 7 Db antenna I found.

3. An Orinoco card and the better 5 Db antenna mentioned in this topic.
...

The abbreviation is "dB" not "Db". The unit under discussion is a "deciBel" which is 1/10th of a Bel. Google for "deciBel" and "Bel" if you want or need more information.

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

Range is notoriously difficult to define with any precision due to many variables. Open space is easily computed, but other things can greatly affect how far the signal may go. For example: "One wall" varies greatly from place to place due construction and materials, which in turn is influenced by things like building codes and climate.

Wall construction varies so much that using identical WiFi equipment, outside your house you might get 200 ft.; and outside your neighbor's house, you might only get 50ft.

Quote:

Originally Posted by Clyde Vargus2

...What's the Db rating of the Orinoco antenna alone? I tried to find it, but nothing I saw stated it specifically as far as I could tell. I think it's 2 or 2.2 Db?...

The card has a rated output of 15dBm (32mW.) I've never seen a breakdown of the internal antenna of the card.

Quote:

Originally Posted by Clyde Vargus2

...If I got the cheap 7 Db unit, could I cut out a circle of sheet metal and put it at the base of the antenna, or is it wired into the unit somehow?

I'm just cheap, that's why I ask this.

Yes, although the cheap high-loss cable will still kill a lot of signal. That's where much of the loss occurs.

10-15-2004	#1 (permalink)
Clyde Vargus2 Registered Member Join Date: Sep 2004 Posts: 28	Are these antennas any good? http://cgi.ebay.com/ws/eBayISAPI.dll...e=STRK:MEWA:IT and http://cgi.ebay.com/ws/eBayISAPI.dll...e=STRK:MEWA:IT With the kind of cable they have, 7 decibels gets knocked down to (how much?) before it gets to the computer?

10-16-2004	#3 (permalink)
Clyde Vargus2 Registered Member Join Date: Sep 2004 Posts: 28	More questions: 1. What is a ground plane - size and shape? 2. How much does the fab corp 5 decibel unit cost (I'll look on eBay)? 3. If I get one, I'll also get an Orinoco Gold Classic card, so it'd have to be able to plug right into it. With no fancy adapters or anything. 4. I've seen the pictures of the shape of the radiated signal from low and high debical antennas. The high decibel units have a much flatter pattern. It seems obvious to me that it would remain the same, but will a 7 db antenna have the same pattern of radiated signal even though the cable loses some of its power? In others words it would NOT have the radiated signal pattern of a 4.3 Db antenna if the 7 Db antenna had a cable that lost 2.7 Db on its way to the card and computer? Last edited by Clyde Vargus2 : 10-16-2004 at 08:13 AM.

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10-16-2004	#2 (permalink)
beakmyn root\.workspace\.garbage. Join Date: Aug 2003 Posts: 4,796	The cable rg-316 has a loss of 0.4 dB/foot = 2.7dB for 6.5 feet rg-174 2.8 dB for 6.5 feet Yes, the antennas will work but they're lossy, cheap and lack a ground plane. They're worth bout $12.00-$15.00 IMHO: You'd be happier with the fab-corp 5dB. I love mine.

10-16-2004	#7 (permalink)
beakmyn root\.workspace\.garbage. Join Date: Aug 2003 Posts: 4,796	Donut Theory not be confused with the episode of The Simpons where Homer tells Hawking about his Donut shape Universe theory. Has some good pictures. My antenna theory is a bit rusty, but two things still hold true. 1. You get what you pay for. 2. The 5db omni from Fab-Corp is worth the money

10-17-2004	#8 (permalink)
Clyde Vargus2 Registered Member Join Date: Sep 2004 Posts: 28	Okay, here's a new question. Range with certain antenna setups. Assuming a standard set of conditions, like one wall of a house and open air space into the back yard / front yard / outdoors in general after that, how far from an AP can you be and still detect it with: 1. Just an Orinoco gold classic card (the only card I'd want to get, based on what I've read about them). 2. An Orinoco card and the cheap 7 Db antenna I found. 3. An Orinoco card and the better 5 Db antenna mentioned in this topic. What's the Db rating of the Orinoco antenna alone? I tried to find it, but nothing I saw stated it specifically as far as I could tell. I think it's 2 or 2.2 Db? If I got the cheap 7 Db unit, could I cut out a circle of sheet metal and put it at the base of the antenna, or is it wired into the unit somehow? I'm just cheap, that's why I ask this.