Is my Ext. Antenna not working? (Agere RoamAbout)

Velox · 09-27-2004

I recently bought an 802.11b Enterasys Roamabout and a 7DBi magnetic mount antenna. Whenever I have the antenna connected I see no difference in SNR as opposed to when I have it disconnected. Am I missing a step I have to take to switch power from the internal antenna to the external? Is something wrong with my antenna? Possibly a break in the line? Or, am I wrong alltogether, and should this antenna not affect my overall SNR, just my range?

Any help would be greatly appreciated.

Thorn · 09-27-2004

SNR should show some increase, as well as an increase in range. The difference should be apparent if you place the laptop and card in vehicle within range of a known AP. Plugging in the antenna should immediately show an increased SNR.

It's just a guess since you didn't say which antenna you have, but it sounds like you've bought one of the cheap ($20-$30) 7dBi antennae with the very small cable (~0.10" dia.) and no ground plane. If that is the case, it's no surprise. The cable has such a high loss, that any gain is negated in the cable. Additionally, those antennae will not function well without a 3' dia. ground plane.

A good mobile antenna in the 3dBi to 5dBi range should cost $50-$100, have a built-in ground plane, and have low-loss cable (~0.25" dia.)

09-27-2004	#1 (permalink)
Velox Registered Member Join Date: Sep 2004 Posts: 1	Is my Ext. Antenna not working? (Agere RoamAbout) I recently bought an 802.11b Enterasys Roamabout and a 7DBi magnetic mount antenna. Whenever I have the antenna connected I see no difference in SNR as opposed to when I have it disconnected. Am I missing a step I have to take to switch power from the internal antenna to the external? Is something wrong with my antenna? Possibly a break in the line? Or, am I wrong alltogether, and should this antenna not affect my overall SNR, just my range? Any help would be greatly appreciated.

09-27-2004	#2 (permalink)
Thorn Did you do the math? Join Date: Apr 2002 Location: Villa Straylight Posts: 10,084	SNR should show some increase, as well as an increase in range. The difference should be apparent if you place the laptop and card in vehicle within range of a known AP. Plugging in the antenna should immediately show an increased SNR. It's just a guess since you didn't say which antenna you have, but it sounds like you've bought one of the cheap ($20-$30) 7dBi antennae with the very small cable (~0.10" dia.) and no ground plane. If that is the case, it's no surprise. The cable has such a high loss, that any gain is negated in the cable. Additionally, those antennae will not function well without a 3' dia. ground plane. A good mobile antenna in the 3dBi to 5dBi range should cost $50-$100, have a built-in ground plane, and have low-loss cable (~0.25" dia.) __________________ Thorn "I'm The Doctor. I'm a Time Lord. I am from the planet Gallifrey in the constellation Kasterborous. I'm 903 years old and I am the man who is going to save your lives and all 6 billion people on the planet below... You got a problem with that?"

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