Antennae, LOS and topo

picothinker · Posted: Mon Jul 23, 2007 9:10 am Post subject: Antennae, LOS and topo

I have been researching EVDO as a dialup replacement. I have pretty much decided on Sprint, as there is a tower 2.06 miles from me. Unfortunately, this is a very hilly area. I have researched and visited the tower (300' guyed) and verified through http://www.wirelessadvisor.com/ that Sprint is only licensed for 1900 mhz in my zip code. When I visited the tower, I could see cellphone sector antennae _about_ halfway up. I would like to find out the height more closely.

I found the owners of the tower in New Jersey (I am in Missouri), but when I called the contact and explained my situation, he wasn't every interested, and brushed me off with a "we cannot give out out customer information (referring to Sprint)". I called Sprint advanced technical support (knowing that local antennae height isn't something they know, but hoping they could steer me). They said call your local Sprint store, and the sales kids there said "try to contact the tower climber/service people for the tower". I know someone who used to be a tower monkey, and left a message with him to see how I could find out. Lacking real information, I may try a simple triangulation method to guess closer.

The reason I want to know the height of the Sprint end, is that I am probably going to have to get an antenna in the air on my end. I am a (former) ham radio guy, and have had plenty of experience with towers and aiming directionals. This is a low-budget project, I have some tower on the ground already, and am just trying to plan ahead as much as possible. Here is the actual topo between my house and the tower. This was guessing 150 on Sprint's end, and I need 30 feet to just clear the dirt.

The Fresnel Zone is the cigar-shaped area around the green actual LOS, and is shaped differently based on frequency. Even if you have LOS, if the fresnel hits dirt/trees/absorbent things it can give you multipath distortion. Multipath in this case will probably mean dropped connect. This map was generated using Radio Mobile, and at the time, I could not run this (it's Windows-only, and I am Windows-free). I had someone else run it for me with my numbers, He used 1900 mhz for the fresnel, but just used the default radios for transmit data and antenna (2.4ghz). I have since gotten Radio Mobile to run under Wine on Linux, and generated this view from above.

At 30 feet, I clear the dirt. There are lots of trees, and at 1.9ghz I know that leaves are a sponge. I cannot have proper guy wires (to hold the tower up), but can have some light guys to help steady it. I can probably get 40 feet of tower up, and maybe 10 feet of mast above it. This will be using a house bracket, and the cube o' concrete at the base (Rohn says 25g tower can supposedly be 35 feet free-standing about a house bracket, but that would be pretty wobbly as far as accurate aiming). This is perhaps borderline, and I know that over time the trees will grow. I will probably be using LMR-400 (although I do still have 30 feet of my old Andrews 7/8" air-dialectric Heliax indoors, and has connectors on it).

And now, finally, MY QUESTION! I have experience with yagi's and aiming them. I wonder if a parabolic would be a better type of antenna, if only for the ice factor? I have read that a yagi, with it's multiple elements (reflector, driver and directors) can be adversely affected by ice more than a parabolic. I have no experience on this comparison. I would rather get the gain with the antenna than use an amp. Or, maybe I should just get the chainsaw out, and have a "Midnight Clearing" of the one spot with trees that will be blocking me.... ;^) Suggestions?
Thanks in advance.

deparson · EVDO Junkie Joined: 30 Aug 2006 Posts: 248

Have you tired a Sprint EVDO card at your home? That would be my first step.

Figure out what kind of signal you have and go from there. At less than 3 miles (clear LOS or not) you might find you are good to go with nothing extra needed at all.

-D

picothinker · Posted: Mon Jul 23, 2007 9:32 am Post subject:

I have a Sprint cellphone, and it is truly lousy at home! Now that I have discovered where the tower is, I can stand outside in a break between my local trees and have (maybe) a little better luck.

Yes, that is part of the plan, to get a functioning card here (and/or on the roof at least) and see what it acts like by itself. This step will be LONG BEFORE putting up tower.

n6gn · Posted: Mon Jul 23, 2007 9:53 am Post subject: Re: Antennae, LOS and topo

xrayman · Posted: Mon Jul 23, 2007 10:05 am Post subject:

You may want to read down through this thread, note the posting by n6gn about a low cost High Performance Die Cast Reflector Grid Antenna.
http://www.evdoforums.com/viewtopic.php?t=5106

mooch · Posted: Mon Jul 23, 2007 10:12 am Post subject: Re: Antennae, LOS and topo

I've seen the "radio link" screen shots in the past but after doing some googling, I've not come up with how folks are getting the graphic representation of what kind of los exists between a tower and their location.

Could someone enlighten me as to whether that graphic is generated from a piece of software or a website?

Thanks!

cpayne5 · EVDO User Joined: 23 Feb 2006 Posts: 71

A lot of people use this these days (including the OP)...
http://www.cplus.org/rmw/english1.html
Radio Mobile Deluxe

--Chris

picothinker · Posted: Mon Jul 23, 2007 11:14 am Post subject:

xrayman: Thanks for the link, i was searching for the mentioned post! I have a 19 db Pacific Wireless parabolic grid, I may try that since it on hand. I wondered about the 1.9 vs 2.4 freqs, but I also know that the higher in frequency you go, most antennae have more bandwidth.

mooch: Those maps were generated with Radio Mobile, linked in my original post and also by cpayne5.

picothinker · Posted: Mon Jul 23, 2007 11:21 am Post subject:

Thanks for the info, n6gn. I knew nothing of the power outout or ERP of EVDO transmissions. I can try three sections and a top section fairly easily, with a house bracket I probably won't have to guy it for stability. If I need more, I have a friend with a gin pole and we can add a section later.

kalen43 · EVDO Heavy User Joined: 30 Apr 2007 Posts: 129

I live just outside Kansas City MO. 1.2 miles from the tower and what little hills we have almost block my signal. I get a barely useable signal. Testing with a card at your place is about the only way to know for sure.

picothinker · Posted: Mon Jul 23, 2007 12:01 pm Post subject:

Speaking of radiation patterns, EVDO/Sprint and so on, I found this interesting plot of a 120 degree sector. Although I have not tried it, it was generated with 4NEC2, available here.