Antenna extension project - multiple zones

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cosmolee
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PostPosted: Sat Sep 12, 2009 4:04    Post subject: Antenna extension project - multiple zones Reply with quote
I have a situation where I need to spread WiFi coverage around a large house. Currently, I have a Linksys WRT54G in the basement. On the 2nd floor the coverage is very bad, probably due to some intervening tin ceiling.

What I was thinking of doing is taking one of the two antennas and extending it with some coax cable up to the 2nd floor, leaving the other antenna attached to the AP to provide coverage for the basement. Thus, there would be two zones of coverage.

I have a couple of concerns:

Will the AP operate using both antennas covering separate areas this way? Some things I've read lead me to wonder if the AP might not operate the two antennas simultaneously and independently. Does it use one antenna for Tx and the other for Rx, in which case my scenario wouldn't work?

From what I gather I'll need to use some low loss cable like type 400 to do the required 70 foot run. Also, I've read that for coax runs of over 50 feet, I will need an amplifier. But could upping the power on the AP obviate the need for an amplifier?

Any advice, correction or wisdom greatly appreciated.

TIA,
Cosmo
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DrJunge
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PostPosted: Sun Sep 13, 2009 19:22    Post subject: Reply with quote
The 2 antennas of the WRT54g are for spatial availability. But it does not work that well all the time, meaning that there are conditions in which the wrong antenna is selected.
Why don't you use a second WRT unit, connected with a Cat 5 cable, for your 2nd floor? The Cat 5 cable is much cheaper than a low loss antenna cable anyhow. If you are really adventurous use 2 back to back WRT units for the second floor: One for the WLAN bridge to the ground floor an one to cover the 2nd floor. I have been using such a configuration for years.
cosmolee
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PostPosted: Mon Sep 14, 2009 6:42    Post subject: Reply with quote
What does that mean - "spatial availability"?

I already have a hub on the 2nd floor, but I was hoping to implement a more "green" solution - ie, without having another unit sucking electricity 24x7 and adding more electronic gadget clutter...

What do you mean by "2 back to back units for the 2nd floor"? How would that be different from simply having 2 units, one for the basement and one for the 2nd floor?
DrJunge
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PostPosted: Mon Sep 14, 2009 10:18    Post subject: Reply with quote
cosmolee wrote:
What does that mean - "spatial availability"?

It means that if one line of sight gets blocked the other might not and thus the antenna is switched to the non-blocked one.

cosmolee wrote:
What do you mean by "2 back to back units for the 2nd floor"? How would that be different from simply having 2 units, one for the basement and one for the 2nd floor?

2 units in the 2nd floor: one doing the link with the basement and one supplying a signal to the 2nd floor. Thus you'll need at least 3 units.
cosmolee
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PostPosted: Thu Dec 17, 2009 2:48    Post subject: Follow up Reply with quote
Just wanted to post a follow up to my project. I did implement the extension of the antennas as I described, and it's working quite nicely. I have coverage in the basement and also two floors up on the second floor.

I made a run of low loss coaxial cable from the WAP in the basement to the second floor, reattached the antenna to the far end of the cable, and bumped up the power to the antennas a bit to overcome the loss from the extra cable.

The hardest part was crimping the connectors to the coax cable. These LLC 400 type cables are fat, and getting the cable to fit into the connectors was a bit of a pain. You also have to be careful to get the correct reverse-polarity connectors for large LLC type cables.

Cost wise, the solution is less expensive than adding 2 more units. Also, I don't now have a second or third unit sucking electricity 24x7, which would have been less green, and this is a simple, straightforward solution to implement. I'm guessing that the extra power boost I've given to the antennas requires less energy than a whole extra 2nd or 3rd unit(s) added.

There are some vendors that provide pre-terminated LLC cables which, if they are in the length you need, would save you the trouble of cable assembly. All in all it was a satisfying DYI project to engage in.

HTH,
Cosmo
DrJunge
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PostPosted: Thu Dec 17, 2009 11:46    Post subject: Reply with quote
Great that it worked. I'll bet that the low loss antenna cable helped. Putting the power up works for the transmission side, but the receiver side of your access point will not get more sensitive.
cosmolee
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Joined: 12 Sep 2009
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PostPosted: Thu Dec 17, 2009 15:19    Post subject: Reply with quote
Yes, the low loss cable was essential to the project. I tried it with some coax used for tv antenna runs - too much loss even when the antenna power was boosted all the way.

The receiver is not more sensitive, but since it now receives from the 2nd floor thorough the basement, the area of reception is extended, and it has a similar effect. ie, whereas there was no reception on the 2nd floor, now there is. There doesn't seem to be a need for changing out to a hi-gain antenna as the original seems to work ok.
BlueScreen
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Location: us-rightside ocean-halfway down

PostPosted: Mon Dec 21, 2009 20:03    Post subject: antenna db Reply with quote
just remember that the "stock" antenna is going to be "without looking" around a 2db and you can purchase a 5db even with no cabling and just replace the antenna you will maximate your wattage, 3dB of change means 2x the power upwards. without factoring in loss of the connector or loss of cabling. Many are only adding an upgrade on the antenna and can see drastic changes to the positive. BUT of course, with wireless there are many factors involved and using the low loss cabling in your situation may have been the way to go.

sorry

just my 2 cents

Blue
JamesThresher
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PostPosted: Sat Mar 06, 2010 21:18    Post subject: Reply with quote
For anyone else wanting to extend the antenna away from the access point, make sure you use 50ohm coax cable (LMR400 is pretty good, but still quite lossy at 2.4Ghz), the TV stuff is 75ohm and the mismatch will cause a much greater loss in the cable (and will put the AP under greater load too which may cause it to fail).
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