Wifi antenna question

[levskipetrov]

I have a customer who needs a wireless connection to their LED sign across a small parking lot. Distance is about 150 feet with line of sight. The sign has two controller cards with onboard ethernet jacks, so I am planning to use a 4 port wifi router installed inside the sign case. I plan to use a 14 dbi directional outdoor antenna mounted on the side of the sign pointed at the window of the second floor where there will be a 7 dbi antenna connected to a standard wifi router.

Here's the question,

Is it necessary to have a booster antenna at both ends of a wifi connection, in this case at the sign and in the office window, or will one work and still do significantlly better than no boosters at all? Is one booster antenna able to receive weak signals better than a standard one?

Thanks!

 

[DrGreen26]

Wow, a 14 dbi directional antenna for 150' that's a bit overkill. Here is my advice. A maxrad or similar mftr 6.5db gain panel antennal will go about 750 feet roughly. 1 14 dbi gain antenna will go at least a mile or more depdning on transmit power..which may be too far considering you only need to get to a sign 150' away.

Rule number 2: When you increase RF Gain on your atenna, your receive sensitivy also increases. Radiation patterns are also important. a higher gain antenna = a tighter coverage pattern but be wise..do some testing and you may even find that omni's on both ends will also work (at full power an omni goes about 600 feet as well)..

Real life example: Your cell phone has a standard gain antenna on it, but the towers usually have a 16db gain sector antenna installed. This allows the RF signal from the cell tower to go 3.5 miles either side of the tower. Your cell phone does not have any gain other that what is standard and the tower can hear you just fine as you drive futher away from it.

I know all of the 802.11 books state that you must balance your RF between client and AP, but they are all wrong..you would only do this if you had a mobile client and that client needed to move further away than the receive sensitivity of the antenna.

Mark C. Greenwood, CNE, CCNA, BICSI II


With more than 16 years experience to share.

 

[levskipetrov]

Thanks for your input! I chose the 14 db antenna because I did not want to buy something that didn't have enough gain. Another question maybe you could lend some insight to is this:

The sign enclosure is a 14 gauge steel frame with about 4" of high density foam around it. I am going to try using the standard router antenna transmitting from inside it and see if that works, but are there some general guidelines to transmitting through different materials such as steel and concrete?

 

[DrGreen26]

Each material type will have its on db signal loss. Best thing to do is measure it...exmaple concrete block walls have about 6db of attenuation while drywall has 3...what you could do is measure the RF signal strength with the enclosure open and then with it closed..this should give you a pretty good idea as to signal loss etc.



Mark C. Greenwood, CNE, CCNA, BICSI II


With more than 16 years experience to share.