Antenna alignment - what's being used?

[G0AOZ]

So you have your two dishes mounted in the clear, say a couple of kilometres apart, now they need careful alignment. How? For very short distances presumably lining it up by sight is acceptable (before you switch it on!). I think satellite TV dish installers usually use a small portable receiver with an "S" meter to position the antenna optimally. I guess this could be fairly expensive so, what if anything, is available for WiFi?


ROGER - G0AOZ.

 

[skotman]

A compas will work.

Scott Heath

http://www.scottspad.com

AIM: orange7288

 

[superjet]

Or if you don't have a compass, you could try navigation by the stars....

OR download Netstumbler (

http://www.netstumbler.com)to

a laptop and plug your antenna into a wireless card that has an external antenna jack. (orinoco is a good choice here)
Netstumbler has a nice little GUI that shows signal strength. I have use this for a line of site shot of over 3 miles.

 

[G0AOZ]

Ok, thanks for that... Haven't actually got the card yet. Was thinking of using a D-Link DWL-660 which has an external antenna connection. I assume this would be ok? Any comments on choice of card? I note the suggestion re Orinoco...

Re Netstumbler, does the GUI signal strength indicator show immediate changes in signal level? I.e. if I suddenly tweak the azimuth of the dish by say 90 degrees, does the screen display respond instantly to show zero signal?

Also, when aligning the dish, what's the best way to get a constant (regular) signal sent by the remote site? Get it to do a continuous PING...?


ROGER - G0AOZ.

 

[tharder]

The Cisco Aironet 350 card is also a good choice for antenna alignment. There is a model with an exteranl connector (LMC). You'll need a pigtail, but then, you'll need that with any card with an external connector to adapt it to your antenna connector.
The Cisco ACU utility(included with the card) is also great tool for antenna alignment, not only for signal strength but tranferring data to look for errors caused by interferance. While on that subject I'll also mention you should check for other radios in your area and avoid those channels.
Cisco also has a real nice FREE tool(xls spreadsheet) that is used to compute signal strength, cable loss, antenna type and freznel zone needed. As you distance increases you'll need to quite a distance above obstructions. The beam pattern between the two points looks more like an egg not like a laser beam....

 

[G0AOZ]

Hmmm, very interesting... One or two folk I've spoken to have not recommended Cisco, but your experience would suggest otherwise. I actually tried setting up the D-Link card (which arrived early this morning), under Windows NT4. The signal strength indicator appears to be pretty useless, and unfortunately Netstumbler is reported as not tested under that platform, and not suitable for D-Link cards! A double whammy there...

Re your comment about other local wireless LANs, I take it that these would only be visible by using something like Netstumbler? Or would they show up in the LAN card software?

Are the effects of the freznel zone likely to be less prevalent using a well focused parabolic dish antenna, than say a yagi, given that both antennas had similar forward gain and both were mounted at about the same height?


ROGER - G0AOZ.

 

[Bobg1]

to compare the differences between the dish and the yagi, you need to look at the specs for each and do a comparison. I suspect that you may find the dish specs to be a bit better on receive as a dish has a larger capture zone.

 

[n3buo]

We have had good luck with GPS to align the Antennas. Another option is to use a phone butt set and transmit a tone. I think the conections are pin 1 and 3 for the tone? I will see if I can find the schematic. We have used this with Cisco products.

Dave

 

[G0AOZ]

Thanks for that Dave - I'll probably look to using the GPS idea. (I'm more used to using slightly lower frequencies, like APRS on 14.103


73 ROGER - G0AOZ.

 

[paradox17]

How far are your points? You have many factors including the Fresnel zone, k-factor (not under 10 miles), reflection point, LOS, multipath, RF interference and others.

What kind of radios are you using?
Most radios come with built in apps to test the radio strength and make sure you are within your fade margin. LOS for the antennas is only part of the set up have you consider polarization?

do not use a yagi for PTP. Use a flat panel or parabolic. Give me some more information about the site and I can help. Also programs like Delorme Topo USA, MS Streets, Keyhole, Micropath, Pathloss 4 and of course a GPS with an altimeter.

hope this helps

 

[G0AOZ]

Not been up to check it out yet, but may not have LOS over the 2km path... Therefore might need a repeater.

Interested to understand why you suggest NOT using a yagi for PTP?


ROGER - G0AOZ.

 

[paradox17]

The only reason I suggested not to use yagi is that you have a better chance of aligning the antennas with a flat panel. A yagi has a more focused beam around 35 degrees approximately (usually). You can certinly use a yagi effectivley for short distances.