Originally posted by: bobdole369
Lets start with this: I'm a ham radio operator, having extensively worked 2m (144mhz) 440, 900mhz, and 1.2ghz in years past. Also HF stuff, but thats not relevant here. I only mention this so folks will understand that I have an inkling of how RF does and doesn't work.
I'm going to take apart some of this post and correct a lot of it, so bear with me.
If you can't see his house or neighborhood from the top of your '50 pole, you are likely wasting money.
Just plain wrong. Lets get it straight - up to about 1.2ghz - line of sight is not absolutely mandatory. The lower towards VHF you go the less of an issue it becomes, but 1.2ghz is sort of a barrier of sorts where you almost NEED to actually see the other antenna.
Case in point - Police radio's. Most are on 800/900mhz band now - trunked systems. The portables they use are 100mw, 300mw, 1W, 5W and all manner of in-between. You do not need 100% signal reception for data to go through. The 900mhz protocol retransmits as needed, so as long as something is getting through, you'll just end up latent. Cop radios almost never get LOS and have to work in all situations. Similar situation in the amateur radio world. I can talk on 900mhz with 100mw in my living room and light up a repeater that sits at 30 feet over 5 miles away with aplomb. You don't need to see the other antenna at all. It is not 2.4ghz where a tree wipes everything out. Forget about that. It's a non-issue in this freq range for all intents and purposes. Sure it does attenuate, but it's NOT 2.4 where the wavelength actually interacts with the h20. It passes basically right through it.
if either of you have 900mhz phones or other devices (not as common as 2.4ghz gear, but still) they can cause interference.
For the longest time 900mhz ISM cordless phones were the most common, though not as common as 46/49mhz devices - those were huge for a decade. Lots of these 900mhz ones still around, likely many more than 2.4ghz. Most are the 5mw/30mw variety. It's ISM - it comes with the territory, you'll be way above most of it and you won't be interfered with much at all.
do you have a weatherproof enclosure for the board/900mhz adapter to be outside with the antenna?
It's not necessary. feed line lengths up to 100ft with LMR400 lose less than 3db. If mounted up on the mast (kinda silly to do it that way at this freq) you lose less than a DB (0.5). If using some of the equip I saw linked you'll lose a couple hundred mw. No issue.
if youre mounting this stuff over the roof line of your house and above nearby trees, please understand that this can attract lightning, and understand that that is a very bad thing when it hits your home.
Now this is terribly, terribly important. I'm assuming that the mast in question is all metal and goes at least 8 feet into the ground (beyond concrete). If not, start pounding ground rods. You'll want several bonded with 0AWG or 1-2inch copper strap in a circle around the mast, going to the mast itself. Give 8 feet radius for this circle and pound preferably 5-8 of these rods 8 feet into the ground.
Now you need arresters on the feedline. These are gas discharge tubes - when static builds up on the antenna It arcs over the gas gap and connects the antenna to earth ground for as long as it takes for the static to discharge. You'll consider the mast itself earth ground. You'll bond the arrester to the mast. If you have the equip up on the mast, you'll need arresters on the power, ethernet, and any other conductor that enters the home.
So Marion will be at the top looking down on Home. There is a 29 foot difference so if Marion uses the rooftop + 5ft that is probably another 35 ft on top of that making it ~ 64 ft higher than you at ground level.
If using an omnidirectional antenna - the other side could be 500 feet below you and it still works. Beamwidth is not an issue here. These aren't lasers.
So if any tree is over 30 feet it will decrease signal strength.
Simply wrong. Might be accurate at 2.4ghz, but not 900mhz.
With that much power, that high up - you could go 10-20 mile radius using a 3dbi omni on both sides.
Not gonna happen.
At VHF and above, foliage (moisture in general) eats the signal.
Line of sight is mandatory, even at 900 MHz.
Wrong, wrong, and wrong.
LOS is nice, but its not the same thing at nearly 2.4ghz. It doesn't even really mean the same thing. LOS at 2.4ghz means you gotta actually see the antenna with your eyes. At 900mhz - you really just gotta see that there isn't a brick wall or concrete or a big steel hangar in the way.
Think of it this way: Your cell phone works in elevators. It has a 300mw or 100mw transmitter. Most phones use 900mhz/1900mhz. If LOS was really that important, you couldn't make a call in your living room.
I suggest using an omni. But something like a 9db yagi is cheap enough and has a very wide beamwidth and is nice insurance.
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