Looking for RF / Communications help

Not knowing the topography of the land and area to be covered by said system, it kind of hard to say yea or nay to said height of antenna. "I" being in 2 way radio "and" Borough code and so on - can only offer that you find a local 2 way radio shop in your area to give you assistance or point you to someone who can. Others might have their own opinions - but that is mine. They have some 800 mhz stuff around here - and many aren't happy with it. Our terrain - hilly - at best.

L.

What the hells a variance? I know the stats but...?

In "Zoning Ordinances" adopted in many towns, cities, etc - each often differing from others in their own ways. Zoning is for Mixed Use, Residential, Farming, Industrial, whatever terms that area gives their zones. A "Variance" is a request to erect a building, tower, place a business in - use the land in that specific zoned area - contrary to the Zoning Ordinances in effect for it. For example - if you have an area of town zoned "Residential" - NO business can open up in that area UNLESS a variance is awarded - via a hearing before the Zoning Commission/Committee. To be awarded a "Variance" the party must prove their project - whatever it is - won't pose "ANY" problems to the immediate surrounding area. Even then, there is no guarantee a Variance will be awarded. That is a variance in a nut shell.

L.

You mean planning permission?

What part of the world are you from?

I am EXTREMELY well versed in this exact issue. I do not have the time to take on additional clients, but if you're in the US, I can refer you to several well qualified PE's. You can also search the

At 800 MHz, propagation is generally line-of-sight so height is a major determining factor. If the applicant has prepared radio propagation coverage maps (and I'll bet they have), request a copy of the study. Or email me the coordinates and I'll run it for you (no charge) at the 2 heights and you can compare for yourself. (Canada/US/Mexico only)

-mpm

Variance is the term used in Oregon, and probably many other US states. Where you're from, "planning permission" may mean essentially the same thing.

It's all a terminology thing. "Township" sounds like an east coast (US) term, but I know that in the part of Massachusetts that I lived for a while the term would be "town", although everyone would have known what "township" meant. Many 100% native Oregonians would be confused by the term "township", and even more perplexed by the notion that you can have a state (like Massachusetts) where every square inch of the state is in a town and the only thing the counties do is provide jail space.

As pointed out by MPM propagation is _very_ line of sight at 800MHz. If there's one misplaced mountain then the extra 65 feet could make life-or-death differences to the people who would be in the radio shadow with the antenna on the low tower.

text -

"Township" is also a land surveying term. Has nothing to do with communities. It's a square 6 miles on a side, divided into 1 x 1 mile sections. A quarter-quarter section is where the term "back 40" comes from. (i.e, 40 acres.)

You'll see "Township" mentioned on Meets and Bounds, and property surveys all the time.

Obviously, the OP is referring to the civil type of "Township" which possibly? has roots in the original surveying, but now means something entirely different. I'll bet a lot of townships have boundaries that lay on original survey section lines.....

-mpm

As others have stated, the only way 800 MHz. is going to propagate (absent one HELL of a solar flare) is line of sight, or what we call radio horizon.

Radio horizon is calculated as d = sqrt (2h), where d is the radio horizon in miles and h is the antenna height in feet.

For your two examples, an antenna at 265 feet will have a horizon of 23 miles and the antenna a 330 feet will have a horizon of 26 miles. Is that extra 3 miles really going to make squat of difference?

This assumes Kansas-flat terrain. As others have noted, hills, large buildings, and the like will affect the propagation. "How much affect" is generally only available with a field test; it is not easily or accurately calculable.

Jim

Well, let's look at Kansas. For convenience, let's start at the Meades Ranch, which is widely regarded as the exact Geographic center of the US Continental 48 states. (It is also the reference point of the NAD-1927 survey datum upon which almost all land surveys are derived, including the State Plane Coordinate systems which were tied to this same reference.)

The coordinates for Meades Ranch are: 38-13-26.686N, -098-32-30.506W

Now lets draw two imaginary lines in space each terminating at a point exactly 30 miles due North of the Meades Ranch. The first line will start at an altitude of 265 feet above the Meades Ranch, and the second will start at an altitude of 330 feet. (Obviously, the lines are different lenghts.)

Let's start at the lower line (@ 265') and travel north.

Along the way, we'll be looking straight down and straight ahead, and hope we don't hit anything.

We can "hit" something in one of two ways: We can run right into it, which would be a line of sight obstruction, or we can hit a changing distance directly below (and above) us that represents an ellipse (Fresnel zone), which is where a portion of the receivable RF energy is spread out during propagation along the path. If either the direct LOS, or the 1st Fresnel Zone get obstructed, radio coverage will suffer. (The extent of which depends on how lossy the obstruction is.)

So, running a quick study, here are the Results for Kansas: (@ 265' first)

We actually get pretty close to a terrain obstruction (including curvature of the Earth) at 8.4 miles out. The coordinates there are

Continuing along, no further significant obstructions occur until we reach a point where the Fresnel zone slams into the terrain at 22.5 miles out. 39-32-39.79N, -98-32-30.51W At this point, LOS is still clear by 94.88'.

Finally, LOS ends (hits Earth) at 25.3 miles out. 39-35-26.95N,

Note: All coordinates here are in NAD-27. Using USGS 3-second terrain data, and ignoring all ground cover (trees, buildings, etc...) Oh, and I'm also assuming a receiver heigh of 3-meters, not that that will affect these calculations in any material way.

Now, let's take the line at 330' above ground level at the Meades Ranch...

Obviously the obstruction at 8.4 miles hasn't moved. But now the Fresnel clears by 105.13' and LOS by 204.44'. (Previously 58' and

The Fresnel will now hit the Earth at 23.9 miles out (instead of

Finally, LOS will now impact the Earth at 25.4 miles out. (instead of

Conclusion: You're right. In Kansas (at least at the Meades Ranch location and on a radial directed due North), height doesn't help you all that much. If the obstruction at 8.4 mi out had been more significant, on a 30-mile path such as this, then of course, that would be a different story.

Also note that when incident angles get low to the ground, scattering occurs.

The above is a very simplified explanation of coverage. On top of all this, you would layer equipment and antenna performance information, transmitter output power, receiver sensitivity data, acceptable fade margins, etc... to really get to what's needed in the way of transmission facilies.

I've always thought of supplementing my income by charging $49.95 for full-color propagation analysis for Amateur Radio Operators printed on

-mpm

The only people cheaper than hams are aircraft owners; if you sold ONE, I'd be surprised. Trust me, I sell to a market where 95% of my customers own an airplane and a quarter of those are hams also. Nice folks all, but tight with a dollar.

Jim WX6RST

-- "If you think you can, or think you can't, you're right." --Henry Ford

Good point Tim, To clarify I am in Southwest Michigan. The term township as I am using it is very much as MPM described it. It is a square geograghical area of about 6 x 6 mi square. The Variance board is tasked with determining the need for deviation from the zoning rules of the township. In this case the township has a zoning rule to limit to antennas of 200 feet. The utility company would like to put up a 330 foot tower next to an existing 300' tower. The township would prefer to co-location on the existing 300' tower at a height of

James

"James" wrote in message news: snipped-for-privacy@e16g2000pri.googlegroups.com...

Here in PA where I'm from - we have "Towns" often referred also to as "Boroughs", "Townships", "Cities". Yes, it "is" a "terminology" thing. Zones are plots of area in the particular town/township/city set aside/planned out/labeled as used for certain types of activity - Farming/Residential/Industrial/Mixed use, whatever term is used. The "Variance" is "permission" to do what is contrary to rules/laws/ordinances opposed to that sort of thing in a particular zoned area - example placing a gas station in a "Residential" area. Variances are rarely permited - although some are granted. Our "Borough" - just this past month - had a man try to establish a business in a "Residential" zoned area - and was ordered to shut down. He "could" have sought a variance, but his chances of it passing were nil, his cost alone to ask for the variance would have been a bit high - close to $1000. In short - he failed to ask all the right questions before he opened it up. He "lost" his investment because of it. Requirements needing to be met in such variances "could" include such things as proving you won't be making excessive noise, won't be causing undue traffic in an otherwise residential area for example, undue parking hardships for residents, etc. It all depends on how the "Zoning"/"Variance" board and it's rules/laws/ordinances are set up. They can and do vary from area to area. Ours are a bit different and perhaps a bit less stringent - as a Borough - than say the City of Pittsburgh just a few miles away. Before our Zoning came into effect, you could do almost as you wished - the Borough had little power to stop you. Prime example - a major Telephone Company wants to install a tower - and has been doing site surveys. NOW - they have to seek permission from the Zoning Commission as to placement and so on. It has a chance of passage - because they'll be putting it in an area marked "Farming/Mixed use" - up on the hill overlooking the town. BUT - they could also be told NO - if anyone is opposed and can make their case for said opposition.

Aside from the "Variance" - if the tower asked about by the OP is for comms for the Utility, it will still have to refer back to such things as Topography (Flat land/Hills, Etc). The terrain can affect their signals and coverage. There ia software available which can plot out a signal from a given area/frequency. Topographical maps, site surveys with radios can be used to gather information to support said need for the tower in queston. There are ways to gather info tto "try" to "support" the case - to build the tower and there are ways to "try" to block it as well. In the end, it will depend on the homework done to support the case - or oppose it - and the Zoning/Variance board members whether it passes or not.

Possibility #3 is for the extension of the existing structure to allow the newcomer to go *above* the top (existing) service. No new structure, probably minimal increase in visual aspect, probably cheaper if it is a *suitable* "mast".

You use the term "tower" - is it a tower or a mast?

Above 200 feet (and in certain other areas such as the glideslope to an airport or helipad, etc..) the FAA will require the tower to be lit with obstruction lamps. (Technically, this is an FCC requirement - for communications structures only - but the FCC basically mandates whatever the FAA Circular requires. (Note that for other structures, buildings, bridges, smokestacks, etc.., the FAA has sole jurisdiction.)

Regardless, it is not uncommon to see local land use restrictions setting maximum tower heights to 200 feet. (In other words, a prohibition on tower lights.)

A tower owner can voluntarily light a tower under 200' but it must still comply with the FAA requirements. You often see this on towers near interstate highways to accommodate Sherrif's helicopter traffic, traffic & news reporting, etc... But tower lights are expensive to install and maintain, so most towers under 200 feet are NOT lighted. Also, some towers > 200 feet are not lighted if in the "shadow" of a taller lighted structure, or otherwise deemed not to pose a threat to air navigation.

As for extending the existing tower, because it is over 200 feet, it will require FAA authoritzation, modification of the lights (major or minor?, hard to tell without more info), and probably a structural analysis of the tower. I assume this is in an area prone to icing, so that is another concern. Also, wind loading will need to comply with the EIA RS-222-G Structural Standards for Steel Antenna Supporting Structures, and possibly other local building codes. If need be, the tower and it's founations can be upgraded (reinforced), if not prohibitively expensive...

In short: Do-able, but not a slam dunk. Also, the tower owner would have to agree to the modification, which would likely depend on the rent the utility company is willing to pay, other deal terms and conditions, and their own future use of the facility.

-mpm

It is a lattice structure with guy wires. I do not see why it could not be added onto but I am no an ME.

mpm snipped-for-privacy@aol.com posted to sci.electronics.design:

Individual hams i think not, repeater clubs is a wholly different matter. Perhaps a direct marketing effort to an appropriate national publication (hopefully more targeted than QST or 73) would find you some business.

JosephKK

OK down here that is a mast - a guyed structure, while the term tower is used for free-standing structures.

Depending on the original design paramteters it may well have the scope for extension, but if the owner doesn't want someone else there he'll be rather coy/reluctant about allowing even an engineering investigation of the possibility.

Yes it would require a thorough consideration of numerous aspects as "mpm" rightly points out, but that doesn't mean it can't be done.

probably

The main limiting factors in the ability of a tower (guyed tower, self- supporing tower, monopole, etc..) are:

Wind loading - As winds hit the structure, the structure and all things attached to it collect the wind and transfer this force to the tower. Many people incorrectly assume that the weight of the equipment is the limiting factor. It is not (unless you have a pretty flimsy tower!). For example, consider one of those old metal garbage can lids. Weighs about 2 pounds or so. Now take that same garbage can and hold it out the window while driving down the Interstate at

Monopoles have the additional problem of overtuning moments because they rely 100% on their foundations to keep them standing. With guyed structures, some of these forces can be transferred into the guy wires, but even then, the guy wire foundations must be investigated when adding loads to the tower.

Round surfaces tend to create less wind-generated force on the tower than flat plate. The amount of force is proportional (by equation) to the size & shape of the surface area. When ice forms on the tower and/ or coax, and/or antennas, this surface area increases, which in turn increases the force (and compressive load - i..e, weight, in the tower legs.)

At 800 MHz (SMR?), the Utility company would probably use 1-5/8" coax and possibly a separate 7/8" line for receive. The antennas would likely be inconsequential, unless placed on mounts far from the centerline of the tower.

I'm not a M.E. either, but I've spent enough time around them on wind- loading issues....

-mpm