Best Antenna Choices

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Sep 1st, 2010
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I'm up the creek the content filter here won't let me mention.


I've an Aironet AIR-AP1252AG-A-K9 and a smallish three-story, 9-unit, wood-frame construction condo building:


Building.jpg


The wired network runs fine, but I want to supply 802.11g and n to all. The switch does POE, I've a power injector, and have configured the 1252 no problem.  The two radios in the 1252 will support six antennas - three 2.4ghz and 3 5 ghz) - but I'm clueless as to what to buy or what to locate them. The roof is easy, as is the ceiling of the basement garage:  both are already wired with Cat 5E.  Locating the WAP anywhere else will require additional wiring that I'd like to avoid, but I'm not averse to hanging upside down by my feet in order to wire antennas, if only I know which antennas to put where.


Of course since the job is measured in hundreds rather than hundreds of thousands of dollars, my local Cisco partner in Seattle won't return my calls. 


Antenna advice would be much appreciated.  I've spent a week becoming familiar with the issues, but am still not confident.  It seems likely much fussing will be involved, and that I might make a false start or two equipment wise, but I'd at least like to increase the odds of getting it right as quickly as possible.


Thanks,

Bryan

Correct Answer by Leo Laohoo about 6 years 10 months ago

Let say I go with your #1 suggestion:  two WAPs with one AIR-ANT2451NV-R each, one in the center of the roof, and the other in the center of the garage ceiling.  That means half the roof unit's signal is being broadcast into space, and half the garage unit's into the ground, right?  The remaining two halves should still penetrate the building?


Don't forget that the if you mount the AP correctly (Cisco logo pointed downward towards the floor) the signal goes DOWN to the floor and UP to the floor above it.  If you mount it on the ceiling, then I'd like to ask if you have anyone working ABOVE the building (nice view!)



Wouldn't some directional solution provide more usable signal?

With such a confined space?  I wouldn't use directional unless you plan to shoot the signals over 2 kms.



Also, your #1 idea leaves potential capacity for four additional antennas - a 2.4 and a 5 on the roof, and another pair in the garage.  Is there anything I do with that to increase the likelihood of good coverage and high bandwidth?

Ahhhhh ... here's the beauty.  The 2451NV is recommended for 1250, 1260 and 3500e because it has SIX pig-tail (RP-TNC) plugs:  three for 2.4Ghz and three for 5.0Ghz.  So one antennae unit can be pluged in to each radio antennae.  Nothing more.

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Leo Laohoo Wed, 09/01/2010 - 15:41
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The entire structure is all wooden, is this right?  Not a single slab of concrete/brick wall?


Have a look at the AIR-ANT2451NV-R.  Here's the link:


http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/data_sheet_ant2451nv.pdf


Pay close attention to the horizontal and vertical azimuth plane.  This will tell you what signal footprint each of the antennaes have.


This model is designed to be used for the 1250, 1260 and 3500e.


Please don't forget to rate useful posts.  Thanks.

1111eastjohn Wed, 09/01/2010 - 16:11
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The entire structure is all wooden, is this right?  Not a single slab of concrete/brick wall?


The basement garage has a concrete shell, but it's all wood starting slightly above grade.

Have a look at the AIR-ANT2451NV-R


Interesting.  One for the entire building?  That's an indoor-only unit, which rules out the roof.  What do you suppose the best location would be?


Thanks much,

Bryan

Leo Laohoo Wed, 09/01/2010 - 16:21
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Look at the horizontal and vertical azimuth plane (aka vertical and horizontal footprint of the wireless signal) of the antennae.  You'll notice that it's as good as going around in the vertical plane (red circle) but a "kidney-shape) on the horizontal (blue line).  I'd recommend you deploy at least two APs.


You have to play around with the location.  I can see few options:


1.  Center of the building on the top-most floor (roof wouldn't make any difference except when doing maintenance) and one on the ground floor.

2.  Top most floor left-most and ground floor right-most.  Not too much or half of the signal will go out of the building.

3.  Two units on the second floor.


If you can deploy 3 units then I can see one option #2 and the third unit will be on the 2nd floor and center of the floor.


Hope this helps.

1111eastjohn Wed, 09/01/2010 - 16:43
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I get the footprint idea...  I think.  I've gone so far as to 3D model some of them and impose them on the cube of the building.  I'm picturing a globular dumb bell shape, the azimuths being round and the elevations tending toward two-lobed.


Let say I go with your #1 suggestion:  two WAPs with one AIR-ANT2451NV-R each, one in the center of the roof, and the other in the center of the garage ceiling.  That means half the roof unit's signal is being broadcast into space, and half the garage unit's into the ground, right?  The remaining two halves should still penetrate the building?


Not that I doubt your advice, but because I've become curious about all this...  Wouldn't some directional solution provide more usable signal?  What am I missing?


Also, your #1 idea leaves potential capacity for four additional antennas - a 2.4 and a 5 on the roof, and another pair in the garage.  Is there anything I do with that to increase the likelihood of good coverage and high bandwidth?


I appreciate your taking the time to get me up to speed.


-Bryan

Correct Answer
Leo Laohoo Wed, 09/01/2010 - 16:52
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Let say I go with your #1 suggestion:  two WAPs with one AIR-ANT2451NV-R each, one in the center of the roof, and the other in the center of the garage ceiling.  That means half the roof unit's signal is being broadcast into space, and half the garage unit's into the ground, right?  The remaining two halves should still penetrate the building?


Don't forget that the if you mount the AP correctly (Cisco logo pointed downward towards the floor) the signal goes DOWN to the floor and UP to the floor above it.  If you mount it on the ceiling, then I'd like to ask if you have anyone working ABOVE the building (nice view!)



Wouldn't some directional solution provide more usable signal?

With such a confined space?  I wouldn't use directional unless you plan to shoot the signals over 2 kms.



Also, your #1 idea leaves potential capacity for four additional antennas - a 2.4 and a 5 on the roof, and another pair in the garage.  Is there anything I do with that to increase the likelihood of good coverage and high bandwidth?

Ahhhhh ... here's the beauty.  The 2451NV is recommended for 1250, 1260 and 3500e because it has SIX pig-tail (RP-TNC) plugs:  three for 2.4Ghz and three for 5.0Ghz.  So one antennae unit can be pluged in to each radio antennae.  Nothing more.

1111eastjohn Wed, 09/01/2010 - 17:48
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Sold! 


With (of course) one (we hope) last question...


I've got one AIR-AP1252AG-A-K9, and this plan requires I acquire another.  No big deal - I'll still come in under budget. 


But it does make me wonder, was the AIR-AP1252AG-A-K9 the best choice in the first place?  I don't want to deal with a controller for such a small network and so need a stand-alone unit, but beyond that, best is better.  I could even return the AIR-AP1252AG-A-K9 I've got. 


Just a thought.


Thanks again,

Bryan

Leo Laohoo Wed, 09/01/2010 - 18:27
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was the AIR-AP1252AG-A-K9 the best choice in the first place?

The 1250, like the 1240 and 1260 is an industrial-grade wireless AP.  It was designed to be deployed in "challenging" environment:  wide open spaces, theatres, cinemas, etc.


I'd deploy 1250 if I want external antennae and the range.  The 1250 has a larger footprint compared to, say, 1140.  And this is the reason why the PoE requirement is 19.5w or PWR-INJ4.


For indoor office environment, 1140 is recommended.


Hope this helps.

pmickelsen Thu, 09/02/2010 - 16:14
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The 1252 is a beast for reliability!  I know of a business around here that had a fire.  The sprinkler system went off.  When the fire department was done, they went in and the ap was up and broadcasting still.  They pulled it down, turned it over, dumped out the water, let it dry, and stuck it back up.  No issues.  The switch, well, different story.

Leo Laohoo Wed, 09/01/2010 - 16:45
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Forgot to mention that if you do indeed use this antennae, you can hide the AP in the roof cavity.  The MIMO antennae can be mounted (with the Cisco logo facing downward to the floor) and it would look like a light sensor or a smoke detector.  So you won't have any issues with vandals.

SOcchiogrosso Wed, 09/01/2010 - 19:48
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While the Ap1252 shows up to 6 possible external antennas, you can only transmit and receive from 4 of the extensions. 2 of the external antenna extension can only receive. So I would plan on 4 antennas, unless you are using some of the antennas specifically designed for AP 1252 with 3 RP-TNC Connectors for one antenna like the AIR-ANT2430V-R


I would also save wireless N for the 5 GHz spectrum, as that is where it will be more beneficial. (Channel bonding in the 2.4 GHz range can cause some issues if your transmit power is not controlled.)


Since you have a Power Injector you might not have a problem, but the 1252 with Wireless N/2 Radios, typically requires enhanced PoE (more then the 14.5 Watts of power defined in 802.3af)


Just things to consider.

1111eastjohn Wed, 09/01/2010 - 22:54
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While I'm tidying up the pre-order loose ends…


Given that the roof is just that - a roof top, and not a cavity beneath the roof (there is none), do you have any thoughts on the feasibility of enclosing an ANT2451NV-R for use out of doors?  The WAP has its own rooftop enclosure, but it's not big enough for two.  It's a shame there's no outdoor-rated equivalent to the ANT2451NV-R.


Thanks,

Bryan

Leo Laohoo Thu, 09/02/2010 - 15:27
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I'm in the midst of installing approximately 900+ wireless access points throughout the 90 or so public schools.  Most of the APs are 1140 but we have installed 1250 for "challenging" environment.  There are times when we have to install external antennas EXTERNALLY and this means we have to provision "weather" enclosures.  One of the things that we've come up with is the antennae cable has to be installed LOWER to the AP and the antennae assembly.  The reason is to prevent moisture from going UP to the AP and antennae assembly that might cause damage.


Funny thing:  We went to a local shop here to look for the enclosure for the 1140.  We found one that fits perfectly (it was designed specifically for the 1130/1140) and we were shocked by the price tag:  AU$400 per unit.  We went back the next day with a pen and paper and we copied the brand name of the enclosure and searched for the net.  The maker is in the US and it cost us AU$110 per unit (P&H not included).  We purchased around 100 units direct from the manufacturer.

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