Mast Mount Sector Antenna

[edwardsjj]

A customer (a truck inspection site) needs Wireless access outdoors in thier truck inspection area. I'm going to install a Mast Mount Antenna outdoors and run a cable to an Aironet 1200 indoors. My question is, do I only use one(1) antenna or two(2)?

[scottmac]

You could do either, as long as you match the settings to the physical configuration (one or two antennas).

Given that your average lot-full-of-vehicles would be likely to cause a fair amount of multipath, personally, I'd suggest two antennas for diversity mode (just making some assumptions).

The absolute best way "to be sure" is a good site survey. Site surveys are always the best way to go if thee's any doubt whatsoever (and good documentation).

But, for the cost of the extra antenna, I prefer to go the little extra expense and use diversity.

Good Luck

Scott

[edwardsjj]

Yes,I agree! However, I've only did indoor installations but, I have always used two antenna's for diversity. Currently, the customer has one Yagi mounted on a 25' pole and the customer is very unhappy. I want to use two Mast Mount antenna's(air-ant2414S-R). I can't find any instructions on mounting two so, I thought one antenna was all you're suppose to use. Does anyone know how to mount two antenna's on one pole? Are they made to mount on the same pole, just on top of each other? Thanks for your help.

[scottmac]

You can mount them one above the other, but with a sector antenna (this one's a 90 degree sector), you won't gain much.

The idea with two antennas is to get diverse paths, to cover shadowed areas, and reduce the potential multipath interference.

A 90 degree sector antenna would usually be used to reduce the covereage area for use with multiple APs covering an area (one 90 sector covers North-East, another East-South, another South - West, and a fourth covers West -North) ... with each antenna connected to a separate unit so that all sectors are active all the time.

In a diversity setup, only one of the antennas are active at a time ... which would cause (at best) spotty performance with a pair of stacked sectors ... usually ont top one will get the best signal.

If you want to use two tight sectors, you really should put the antennas at roughly the same level, in two different locations (horizontally separated).The separation can be as close as ~5 inches, or a few feet / yards / meters.

You haven't provided much information, but (I'm guessing here) it sound like something like a 180 degree patch / sector would be better, but they should still be horizontally separated (versus stacked) for best diversity performance.

An alternate would be a "Diversity Panel" style antenna, which has two antennas in a single mount.

Here's teh spec sheet for the antenna you mentioned:

http://www.cisco.com/en/US/products/hw/wireless/ps469/prod_installation_guide09186a008024d28b.html

Here's teh link to the available Cisco antennas:

http://www.cisco.com/en/US/products/hw/wireless/ps469/products_data_sheet09186a008022b11b.html

You options (with Cisco equipment) seem to be something like the 2012 or the 1729, depending on the area to cover and max range.

Another option might be a high-gain omni, you expand the coverage area, but you could mount them side-by-side on the same pole (on stand-offs to get some separation and get some diverstiy advantages.

There are other vendors for antennas that might be a better fit, try a Google search on "802.11 antennas."

You must be careful when using non-Cisco antennas: The federal agencies usually approve 802.11 equipment (non-licensed spectrum) as "systems" - changing a component of the systems (including the coax) may push the system out of legal spec.

If you can describe the nature of the coverage area (width, depth, probably antenna height natural obstructions, etc) we might be able to dial-in something a little closer to your needs.

Good Luck

Scott

[edwardsjj]

Thanks for you assistance. I made an on-site visit.

The customer wants wireless access in a 30 ft diameter area, about 125 yds outside their front door. It's pretty much an open line-of-sight with the exception of a few concrete jersey walls along the path to the coverage area and the actual coverage area has a concrete canopy over top of it. The customer wants to do Truck/Trailer inspections with wireless PDAs underneath the canopy. During the inspection, the big trucks are between the antenna and the PDAs. Currently, they have a Yagi mounted on a 25 ft pole, just out side their front door, pointed toward the canopy, and are not happy. The customer reports frequent disconnects.

I’m going to suggest putting an off-set mount on the pole so, to horizontally mount two Ant-24120s for diversity. What do you think?

[scottmac]

I'm not sure diversity will help you for this situation ... at least not diversity parallel to the orientation of the trucks. Trucks cast a pretty big RF shadow.

What would probably be better (from the sound of it)is an AP on the other side of the truck (the shadowed side) using either a wired connection, or using it as a repeater (given that line-of-sight can be maintained between the two APs).

The new AP can have a sector or very directional antenna to prevent sending the signal all over the neighborhood.

The new AP could be an old 350, or a new 1100 ... you're really just trying to get a decent signal to the shadowed area. If this is a high-throughput application (like a very dynamic GUI), the repeater function will reduce the throughput by about half and you might notice the speed reduction.

If it's something like a scanner or PDA, you probably wouldn't notice much of a difference.

Again, a good site survey, or at least a pilot trial should give you the ultimate answer.

Good Luck

Scott

[edwardsjj]

Thanks. I think you’re correct about diversity not helping in this situation. Getting an AP on the shadow side of the trucks is probably the best solution.

However, running a hardwire to the coverage area is not an option. And the apps can’t afford the speed reduction hit of a Repeater. I’m going to setup a wireless bridge. I’ve never setup a bridge before so, I have a few questions I hope you’ll help me with.

First, I’m going to use Aironet 1310’s. I’m going to use the existing, pole-mounted Yagi and attach it to the new 1310 box mounted indoors. Mount the non-root bridge box in the coverage area, just underneath the inspection canopy so, that it’s still above the trucks/trailers but also, on the shadow side of the trucks. I’ll use the integrated antenna and I’ll configure that box as a non-root bridge & AP.

My questions, does the Aironet 1310 box using the integrated antenna need to be in direct line-of-sight of the Yagi? After review of my on-site pictures, there is a 3ft diameter concrete pillar in the bridge path.

Do you know, if configuring an Aironet 1310 simultaneously, as a Non-root bridge and also as an AP, the throughput takes a big speed reduction hit? (Speed is a concern in this situation.) If so, do you know if I could configure the 1310 just as a non-root bridge and use a cross-over cable to a 1200 AP. Thank you for all you help.

[scottmac]

Line of sight is critical ... especially with a narrow beamwidth antenna ... not much "splatter" to recover.

Unless you already own the AP stuff, you might be able to work some magic with a dual-radio AP ... use the 2.4 for the local scanner / PDA / portable ... and the 5G radio for the backbone.

You'll still need line of sight, but the rubber duck should be sufficient to cover the area (site survey), expecially if it's well above and maintains the LOS to the portable device ... the paddle antenna used for the 'a' radio (on the 1200) acts as a patch antenna when it's folded against the body of the AP, and an omni when folded away from the body.

If you can orient the AP such that it faces the main building, you may have enough gain in the paddle (acting as a patch) to make the stretch to the main building (site survey).

If the position and/or orientation of the AP is such that you can't get LOS, then an antenna with an extension cable should work OK ... you may need to get a higher gain antenna to overcome the signal loss of the cabling.

I believe the newer IOS will permit simultaneous bridge/AP modes. I don't know what the effect on performance would be. I suspect it's a little slower (similar to having a 'b' node on a 'g' network) because of the mode switching.

If there's absolutely no way around the pillar with direct LOS, you may be able to work some magic with a reflector (basically a metal plate hanging perpendicular to the ceiling to bounce the signal around the pillar. Not pretty, lots of loss. Possible if you have enough signal margin for the path. 2.4 and 5G signals bounce pretty good, and the distances are close enough that there shouldn't be much dispersion before the bounce. A tight, high gain antenna would help if that's the chosen method.

Al-in-all, it sounds like a good time .....

Good Luck

Scott

[edwardsjj]

Thanks for everything! I’m getting a better idea of what I’m going to do now. Please, just a few more questions.

I’m going to use 1310s. Mount the root box indoors, attached to a 13.5 dBi Yagi mounted outdoors, on a 25ft pole pointed towards the truck inspection canopy.

Mount the receiving box, on the truck canopy ceiling, on the shadow side of the trucks/trailors, attached to a 13.5 Yagi mounted, on top of the truck canopy, pointed back towards the main building. I’ll configure the receiving box as a bridge, and also, as an AP.

I’ve never configured a 1310 before. My idea here is to have, the AP part to allow access for clients (PDAs) and the bridge part to allow access back to the main building. Does that sound like that would work well?

Also, would I gain anything by using two Yagi’s on the main side end verse only using one?

Thanks again.

[scottmac]

I believe it will work.

Using two yagi antennas probably won't help much.

Keep your cable lengths as short as possible. Don't forget to use protection around your external connectors.

Good Luck

Scott