question on masts

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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
the salesman sold some ethernet radios for use in a project of mine.

normally, we only use wifi and only indoors, so the standard wifi installs work ok.

these radios are 900 MHz and will be outdoors. they will have to go on a pole (a mast of sorts) so they are up on top of the building.

I am pretty sure no one told the end user about these poles he is going to have to install.

I am thinking a 20 foot piece of 2" EMT bolted to the side of the building is about as cheap as it gets. That also gives us someplace to route the POE cable that goes up to the radio that is up on top. I am not overjoyed with having the radio where I cannot get to it, but that is what was sold.

I don't want anything elaborate and costly as there is no money for any of this in the budget. Anyone have a better idea?

I am not even sure how high the masts would have to be to get up over the roof so the buildings are not in the way. I can change out the POE cables to be up to 300 feet long. I am really thinking about 10 feet above the roof line would probably work OK. is ten feet of unsupported EMT going to be able to take the wind load?
 

iwire

Moderator
Staff member
Location
Massachusetts
When we install antennas for fire alarm systems all we need to be is above the building, not below. No real mast, the base of the antenna ends up just a few inches above the building
 

iwire

Moderator
Staff member
Location
Massachusetts
Here is a typical example of the ones we deal with.
 

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GrayHair

Senior Member
Location
Nashville, TN
The term 'ethernet' leads me think these are point-to-point units, so line-of-sight may be required, particularly at 900 Mhz. A reflected signal can be your friend, but can also bite you.

Depending on the wind load presented by the device, probably included in the specs, EMT may not be the best choice for a mast. EIA-222 and UBC both address wind loading.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The term 'ethernet' leads me think these are point-to-point units, so line-of-sight may be required, particularly at 900 Mhz. A reflected signal can be your friend, but can also bite you.

Depending on the wind load presented by the device, probably included in the specs, EMT may not be the best choice for a mast. EIA-222 and UBC both address wind loading.

they are more or less LOS, but the radio manufacturer claims it is not an absolute thing. they are pretty close together (no more than about 1600 feet maximum from what I can tell on Google earth). Each of the radios has an omnidirectional antenna.

I am trying to avoid getting involved in the masts as much as possible and pawn it off on the EC if I can as there is nothing in the job on our end for these items.

maybe I will suggest a 2" RGS mast instead of EMT. I'd rather have something simple rather than the tripod design another poster showed pictures of. a 2" pipe strapped to the outside of a wall is about as simple as it gets.
 

mpoulton

Senior Member
Location
Phoenix, AZ, USA
LOS is more important than elevation

LOS is more important than elevation

At 900MHz, line of sight is very important. Elevation is only a tool to achieve line of sight, or get closer to it. Your signal may be able to penetrate light foliage or even some very light wood-frame construction (with no stucco, foil-backed insulation, metal siding, or other obstacles to radio waves) but that's about it. If there are no obstacles then you don't need the mast at all. If you can see one antenna from the other antenna, then elevation is totally irrelevant. But with anything in the way it becomes quite helpful to get the antennas at both ends up higher to minimize the amount of "stuff" between them.

You really should do some testing on site with the actual equipment to see what works. It's highly site-specific. I ran a 1 mile wifi link to provide internet to a jobsite office trailer using only consumer grade routers. I had a 14dbi planar array antenna at one end and a 24dbi dish at the other. Both were placed just above the rooflines. That setup worked fine for over a year with great reliability. On the other hand, I am currently trying to figure out what to do about a failed attempt at a 1.1 mile wireless link between two buildings. Each end has a commercial grade P2P link transceiver with an 18dbi dish on a roof-mounted 10 foot mast, but they can't talk to each other. There's nothing but a few trees in between but that's enough to screw it all up.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
On the other hand, I am currently trying to figure out what to do about a failed attempt at a 1.1 mile wireless link between two buildings. Each end has a commercial grade P2P link transceiver with an 18dbi dish on a roof-mounted 10 foot mast, but they can't talk to each other. There's nothing but a few trees in between but that's enough to screw it all up.

Is there anything off the direct line of sight that you can bounce the signal off? Construct a passive reflector?
Back to back directional antennas at an angle?
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
Placing the radios at the top of the masts, where they will be fairly inaccessible, will greatly annoy someone at some point. Why not mount the radio (and presumably it's weatherproof enclosure) down at rooftop level, and run a coax extension lead from the antenna port on the radio out to the antenna on the top of your pole? It's less mass at the end of the mast, so that would probably let you use EMT instead of rigid. The radio will be serviceable without a Genie lift or removal of the mast too. If the radio can't have the antenna remote-ed, find another radio. Every 900MHz Ethernet radio I've come across allows for remote-ing of the antenna.

You will need high quality coax cable with the proper connectors, but places like www.l-com.com can supply those, no problem. Make sure to get coax that's impedance matched with the radio and antenna; it's almost always 50 ohm, but very occasionally, I've seen 75 ohm spec-ed.


SceneryDriver
 

mpoulton

Senior Member
Location
Phoenix, AZ, USA
Is there anything off the direct line of sight that you can bounce the signal off? Construct a passive reflector?
Back to back directional antennas at an angle?

Nope. It's through a neighborhood, with no really large buildings around to use as a reflector. I'm going to try more elevation, but I can't really go more than another 10' and I think that will still be through the trees.
 

TommyO

Member
Location
Sunnyvale, CA
Each end has a commercial grade P2P link transceiver with an 18dbi dish on a roof-mounted 10 foot mast, but they can't talk to each other. There's nothing but a few trees in between but that's enough to screw it all up.

Would another location on the property get you away from the trees?
Are the dishes pointing correctly? (I expect it would be really hard to tell if you can't visually see the other antenna) And the elevation as well as the azimuth matter. It doesn't take a very steep hill for there to be a significant elevation difference.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Placing the radios at the top of the masts, where they will be fairly inaccessible, will greatly annoy someone at some point. Why not mount the radio (and presumably it's weatherproof enclosure) down at rooftop level, and run a coax extension lead from the antenna port on the radio out to the antenna on the top of your pole? It's less mass at the end of the mast, so that would probably let you use EMT instead of rigid. The radio will be serviceable without a Genie lift or removal of the mast too. If the radio can't have the antenna remote-ed, find another radio. Every 900MHz Ethernet radio I've come across allows for remote-ing of the antenna.

You will need high quality coax cable with the proper connectors, but places like www.l-com.com can supply those, no problem. Make sure to get coax that's impedance matched with the radio and antenna; it's almost always 50 ohm, but very occasionally, I've seen 75 ohm spec-ed.


SceneryDriver
My first thought when I saw what our salesman had sold was to do this. However, the radio company salesman said that there is a lot more loss in the antenna coax than most people realize and it is much more costly than the POE solution.

Maybe some kind of 3-5 foot high tripod can be put on the roof. I will see what the end user thinks. It is his problem as far as I am concerned as he is responsible for installing them. A lot of facilities are pretty skeptical about installing anything on a roof.

something like this maybe.

http://www.channelmaster.com/TV_Antenna_Tripod_Mount_p/cm-3092.htm

I am not sure it makes any real difference though. I don't know if there is any easy roof access. It may be that a bucket truck would be needed to get up there anyway. I don't see any hatches or doors from the google earth view.
 

mpoulton

Senior Member
Location
Phoenix, AZ, USA
Would another location on the property get you away from the trees?
Are the dishes pointing correctly? (I expect it would be really hard to tell if you can't visually see the other antenna) And the elevation as well as the azimuth matter. It doesn't take a very steep hill for there to be a significant elevation difference.

The trees are in the areas between the two locations, not directly adjacent to either antenna mast. I have some options for exactly where to place the mast at each end, but I can't move the trees in between. Antenna pointing is optimized. The units get enough signal to use the RSSI reading to adjust aiming, but not enough signal to actually send usable amounts of data across the link. I'm thinking about switching to much larger dishes. I need about a 20db improvement in SNR to get a good data rate. A 30dbi dish at each end should achieve that, but that's an annoying antenna to handle.
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
If you need a taller mast, consider guying your tower with cables. That will give you a much taller possible height, even using a relatively small diameter pipe. If you need to couple any pipe sections together, DO NOT use threaded couplers. Since the NPT threads are tapered and deep in pipe wall cross section, they present a weak spot that will break in bending; I see this all the time in pipes used for theatrical lighting (one of the things I do for a living). You need sleeves with cross bolts for a structurally sound connection.

Where is this project located? I also do rigging (among other things) for a living, and this sounds like a neat project.

If EMT or even rigid won't do it, antenna truss may be helpful:

http://www.solidsignal.com/pview.as...=google_base&gclid=CLHpy5yCp8sCFQFkhgoda4oODQ

At any significant height, you'd have to guy it, and most likely get a structural engineer involved to ensure you didn't overload the roof. Probably massive overkill for the wee little antenna and enclosure you need to support, but it's possibly an option. It's never simple, is it?


SceneryDriver
 

mpoulton

Senior Member
Location
Phoenix, AZ, USA
I ordered higher gain antennas. They're 24dbi which only gives me an improvement of 12db total over the existing dishes, but I rechecked the SNR and I think this will be enough. If not, then I'll raise the masts and go from there.
 

tom baker

First Chief Moderator
Staff member
I have a lot of experience in this area...

Test the signal path with the actual radios, most have some type of signal strength meter

Minimize the coax run, at 50 feet you will loose 1/2 of your power (or 3 dB)

Trees are usually OK, it depends on the type of leave, and time of year.

If these are unlicensed, you may have issue with all the other RF in the air, don't know until you try.

I use water pipe for my masts (have done around 50), as the water pipe is heavier wall than RGS, and comes 21 ft long. I typically use 2", there is a bracket at the bottom with a bolt to so it lay down, then a bracket to the wall, often the antenna will be above the building, but can be lowered down for maint.

Use gain or yagi antennas.

For coax I use Times Microwave LMR 400, it has a bending radius of 1" and I run the coax thru the pipe and a weather head at the top.

You'll need to ground the mast to your GES and install an impulse suppressor on the coax, connected to the GES

One of the pictures shows a winch that I use to lower the mast, that 2" water pipe is heavy!
 

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