It really all depends on the antennas (which I see you didn't list), most high DB increase directional antennas have to be aimed very closely, can't even imagine why you have those, I use em for 5-10 Kilometer links, not a lousy 600-700 FT (sorry, 200 meters). Seems to me you are doing a way overkill antenna situation. A Semi directional (very cheap/small, don't need masts, and usually only has to be aimed within 5 degrees, those high gain yagi's usually have to be aimed within a degree or so) work extremely well and are very cheap for shorter links.
Ok. I'll try not to be insulting. I really do wanna vent my wrath as I'm having a truly rotten day, but I'll try to be nice.
You can help if you supply the URL.
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That's probably overkill for only 200 meters.
Look up the data on your 14dBi yagi antennas and dig out the -3dB beamwidths. My guess(tm) is that it's about 30 degrees. From experience, I found that about half the beamwidth is necessary for a reliable signal. Therefore, you can miss by about +/- 7.5 degrees at each end.
You'll be surprised how little 7.5 degrees is. Make two lines on a piece of paper with a 7.5 degree angle, and see for thyself. Aiming a fairly short base antenna, without a boresight, on top of a pole, to within +/- 7.5 degrees is not easy.
How much downward? If over 15 degrees downward, you won't have any signal. Also, such sloppy installations tend to move around, usually for the worse. My guess(tm) is that the U-bolts that came with your antenna are too large for the small pipe you have it mounted. Take a piece of steel (not aluminium) angle or C-channel, cut to about 6 inches, and jam it between the u-bolt and the pipe to increase the effective diameter.
Today, probably no effect as there's enough surface area between the connector and the shield to make a tolerable connection. However, such an air gap is an invitation to water incursion. You'll have fatal problems after the next rain. Worse, your unspecified coax cable could be ruined by the water, or may need to removed to bake out the water. LMR-400 crimping tools are about $40 and a good investment as I've seen far too many sloppy crimps.
For waterproofing, I suggest you find some 1" wide teflon tape. Wrap the tape around the connector(s) with about 50% overlap. Then cover the TFE with Scotch 66 or Slipknot Grey electrical tape. The TFE will cold flow into a good seal, prevent capillary action from sucking in water, doesn't make a mess, and is easy to remove.
No. A laser pointer is very difficult to aim if you cannot see the target dot on the other end. If you can, then by all means, use it. However, I prefer a cheap rifle telescopic sight, a USB camera, or both, for alignment. Also, buy a bubble level and use it to get the vertical elevation correct.
Incidentally, I built an electronic inclinometer using an electrolytic tilt sensor. It's very handy when I have to adjust the elevation of a highly directional antenna on a tower, where I have to be both behind the antenna for adjusting the bracketry, and simultaneously in front of the antenna, for viewing the level.
I'm a newbie in need of some suggestions. I have a couple of Pheenet WL-
522BA access points (just in case anyone recognises them) linked to 14dB directional yagi's roughly pointed at each other with a gap of less than
200 metres.
I'm having loads of trouble getting a reliable signal. How precisely will these need to be pointed at each other? If one is pointing slightly downwards and the other isn't, will this kill the signal? If an N connector wasn't crimped absolutely tightly, how much difference would that make (the outer shield, not the pin)?
I'm considering attaching a laser pointer to one of the antennas and looking for the spot on the opposite wall and then following it up the mast. Would this work or is there a better technique for alignment?
Hmmm... $100/ea. Can you really see the beam as a line? If so, targetting should be fairly easy. Thanks for the er...ah pointer.
Well, actually I did have a way to use an IR laser. I have a night vision scope with an IR filter. If conditions were perfect (fairly dark, lots of dust, smog, or fog, and no nearby lights, I could see the beam out to about a 3km. Projected dots were good to about 5km. Not great, but still useful.
Yes, but the digital contractors levels all have the same problem. I can't see the display while I'm aiming the antenna because it's on the other side of the dish or panel. The one I build uses a seperate electrolytic tilt sensor, about 20ft of wire (setup as a Kelvin bridge), and a home build instrumentation (balanced) opamp. Output is on whatever DVM I can find. Calibration in degrees is by a simple lookup table. I'm usually not interested in exactly how many degrees of incline, as I am trying to get something exactly horizontal.
One really nasty problem I run into often is that many dish and yagi antennas do not have their major lobe aligned exactly with the boresight. They can be off as much as 5 degrees. That's due to construction asymmetry, lack of a balun, coax radiation, or just plain sloppy assembly. With panels, it can be caused by phasing errors between patches. A yagi with the elements mounted on the side of the center boom, instead of going through the middle of the boom, will be misaligned. I use a conventient RF source on a nearby mountain top to test the boresight alignment and tag my antennas with any discrepancies. That saves considerable guesswork during installation.
On Wed, 19 Jan 2005 13:14:37 -0800, Jeff Liebermann
You might take a look at the new green laser pointers. I bought one awhile back from here:
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This is the most visible beam I've ever seen from a handheld unit. The beam itself is visible off-axis in low light. The reflected spot from buildings can be seen in the daylight for at least a quarter mile and well over a mile at night. Reflected from reflective film such as on street signs, the beam is visible literally as far one can see the reflector. I've used it to shoot a locating beam from a mountaintop to an observer on the receiving end over a path length of almost 10 miles.
I bought this thing primarily as a long distance aiming aid and it works beautifully. All past impressions of handheld lasers go out the window.
Nifty. Lowe's has a commercially made version available. Some stores carry it, others special order. I have one. I think it was about $60. The display resolution is 0.1 degree. I have no way to measure the accuracy.
The actual beam is visible at night. It can be seen for some distance in overcast conditions if one looks practically down the boresight of the pointer. The spot is so bright, however, that even in direct sunlight, one can aim the beam at something close below the target and then walk it up to the target. I can do that by hand up to about a quarter mile. Beyond that I have to mount the thing on a viscous head video tripod and slowly pan up.
Slick. I like that idea. I bet one could take one of the commercial units and tap the analog signal before it goes to the A/D and bring that out to a connector that could connect to a voltmeter. That would be a way to do it without having to build from scratch. If I can find mine, I might just give it a shot.
Unfortunately, the examples are for US stuff, and for your situation, and looking at that same website (obviosly you can buy from them), they have two outdoor panel antennas listed (as in stock)
NET-WL-ANT008PN 8dB Directional Panel with flush wall-mount and N type Socket connector* or NET-WL-ANT010PN 10dB Directional Panel with flush wall-mount and N type Socket connector
============================= With any luck, by going to the same company, you may be able to get a credit on what you already have, and trade it in for the new stuff. Chances are the connectors etc will also be the same.. You may want to give that a try first.
Why the difference in signal/radiation etc? Basically (not exact, but hopefully something you can picture in your mind and understand) think of a normal omnidirectional antenna, putting the power into radiating into a 360 deg spherical circle (think basketball).. Now use a semi directional antenna that only radiates in 180 degrees (think basketball cut in half), the output power is doubled into 1/2 the radiation pattern, and the range increased. Cut it in half again (90 degrees), and you double the output power/range in one slice.... now cut it in half again (45 degrees, smaller radiation area, same power) and again going into a beam about 22 1/2 degrees)... etc etc etc Remember, you are still radiating energy from top to bottom (180 degrees), you can narrow that down too.... Finally you end up with the above (directional panels), that focus all the power into a much smaller area, the difference in the DB is one has a tad smaller beam/pattern/area than the other. The yagis, are very small beams (usually 1 or 2 degrees), so you have what is normally radiated in a sphere, concentrated into a degree or so beam/area/smaller pattern/etc.
Again, the above is not meant to be a technical description, just a sort of generic overview/idea.. For your needs, (between buildings) I would look at a flush mount directional panel like listed above.. Easy to install/aim/etc, doesn't need any fancy equipment, and easily gives you the power you want/need.
Since Tim already has the yagis, if he gets them pointed correctly, he should get maximum throughput and weather loss margin, shouldn't he? There's also some guard against snooping if he's running a tight pattern.
Otherwise, some broader pattern would be easier to set up, but if he already has these...
True, except the numbers are wrong. Theoretically, if you assume that the horizontal and vertical plane patterns are roughly symmetrical about the boresight axis, then the -3dB beamwidth of a yagi antenna varies directly with the gain. For example: gain -3db beamwidth dBi degrees 8 60 10 40 14 30 16 25 I dug these numbers out of assorted yagi antennas that Google found.
Reality is not quite so neat. Different yagi's have different efficiencies depending on construction, mounting, type of match, and design optimization. They could have side lobes that cause some gain to be lost. They could be optimized for bandwidth or F/B ratio, instead of maximum gain. The pattern between -3dB points to be "lumpy" and not very smooth. Lots of ways to screw it up. However, in general, the numbers are fairly close.
So, how close does one need to aim an antenna with XX degrees of beamwidth? Well, if the pattern is rather "lumpy" between -3dB points, then probably within the width of the major lobe. That can be as close as +/-1 degree. However, if the pattern is rather smooth, my rule of thumb is +/- the -3dB beamwidth. For the 14dBi yagis mentioned, that within +/- 7.5 degrees.
The next question is always, what about different types of antennas? Do they all have the same beamwidth for a given gain? Nope. For example:
Type gain -3dB Beamwidth dBI degress patch 13 38 yagi 14 30 planar 13 25 dish 15 19
I lifted these numbers from the fab-corp web site for various types of antennas. They're not exactly the same gain, but close enough. Note the wide variation in beamwidth. What's happening is that each type of antenna has varying vertical horizontal symmetry and efficiencies. They will trade something for more gain. If that's efficiency, such as the 50% reflection efficiency of a dish antenna, it will show up as a narrowing of the major lobe, which is the beamwidth. In general, the less times the signal has to be re-radiated (yagi) or reflected (dish), the more efficient the antenna, and therefore the wider the beamwidth for a given gain. Another really bad, but functional rule of thumb is that for a given gain, the less metal in an antenna, yields the wider beamwidth.
Narrow beamwidth isn't necessarily a problem. It does make aiming a bit more of a challenge. However, it also reduces interference pickup from the sides and multipath reflections of buildings and the ground.
I agree. In my never humble opinion, patch and panel antennas are the best compromise between volumetric efficiency, aesthetics, beamwidth, bandwidth, price, and easy of installation.
My experience with yagi antennas on 2.4Ghz has not been good. I've had problems with boresight misalignment, narrow bandwidth (usually caused by a crappy matching circuit), high VSWR at band edges, mounting droop, and the ultimate challenge...birds. There's something about a yagi antenna that birds can't resist. A layer of bird droppings on a fiberglass radome covered yagi does not really affect the signal, but it does make a mess.
There's also a question of dB gain vs price. Yagi's are comparatively complex antennas for the gain delivered. Patch and panel antennas are rediculously simple. Again, lifting numbers from the fab-corp web site using the cheapest antennas in each class:
Well, that didn't turn out quite what I expected thanks to a drop in dish prices. Still, it shows that you get the most bang (gain) for your dollar with a dish, with the patch being a close second. Least cost effective is the yagi, thanks to complex construction.
Yep. A fast calculation, with LOTS of guesswork thanks to the usual inadequate information yields: tx power: +13dBm tx coax loss: 3dB Distance: 0.1 mile Rx Sens: -79dBm rx coax loss: 3dB yields about 34dB of fade margin. That's about 12-15dB more than really necessary, but a good thing to have. The rx signal level at the receiver will be about -50dBm, which is wall below the approximately -30dBm overload point.
Sorta. Yagi's have nasty side lobes. There will be off axis places where something can be heard.
That's why I originally suggested that something else may be wrong (i.e. water incursion, coax, connectors, etc). At 200 meters, it should work even with somewhat misaligned antennas.
Just to keep all you suggesters informed. With a little bit of tweaking on the height, we seem to have a very reliable connection. This is before trying to align things more scientifically with a rifle sight. I could tell you how good the signal is if my access points provided a signal strength indication but they don't (do any?)
Interestingly, my PC inside one of the buildings is registering a 20% to
30% signal through it's PCI wireless card with the standard stubby aerial. I didn't expect that.
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