Antennas and surrounding metal structures

[tim]

If the LoS passes close to other metal objects will that affect the radio patterns.

I have a Pac Wireless 5.8 GHz parabolic, about 1 metre in front of it and slightly to one side is a domestic TV antenna, I am getting poor SNRs and am wondering whether it could be the TV antenna distorting the tx/rx in someway.

[lonnie]

I would suspect some issues but not enough to cause major problems. How weak is the signal and how far away? What radio/antenna is at the other end.

[tim]

A - B - C

A to B is 13 miles 5.8GHz with PacWireless 29dB SNR 14 to 20 dB
B to C is 13 miles 5.8GHz with PacWireless 29dB SNR 0 to 6 dB


The LoS's are both good, both are marine links, exactly the same config on the two configs, the only difference is that C has a TV antenna in front of the antenna (about 1 metre away) and slightly to one side.

I am about to put CM9's in instead (currently all links are Atheros 5354's), and hopefully that will boost the signal sufficiently.


I am still very puzzled by the high tide effect, I saw that someone else was also seeing it. It is particularly bad when the sea is mirror flat, which it has been over the last few weeks. I see exactly the same effect with 2.4 & 5.8, and for different links. It seems to improve when I use h-pol.

I cannot believe this is a multipath effect, as I would expect different results with different frequencies and links.

So why does it get worse for Spring tides ???

[lonnie]

Let us know about the CM-9 improvement. Is there any chance you can raise the 5.x antenna? Or can you move the TV antenna to the side or even put it on the same mast above oe below your stuff?

[mp3turbo]

hi Tim,

like Lonnie said, we all are waiting for your results :) btw, you also could try to point antennas on both sides little bit more skywards - could help by lessening refraction from water.

bye, mp3turbo.

[tim]

I am afraid the jury is still out on this. I've got a good 6 to 8 db gain on one link and the db seems to be more stable with less fluctuations.

The problem link is still a problem, I've only put a cm9 in at the near end, I'll be putting the second cm9 in tomorrow, so I'll let you know what happens, but I'm suspecting cable/connector issues.

All the links are approx the same (13 miles) I'm getting 20 db on two of the links and a miserable 2 to 4 on the problem one.


I've put a url in which shows the signal strength on the improved link. It's a live url so will change. The outage spike at 20:00 wednesday of week 24 was when I changed both ends from 5354's to 5004's. Sorry about the scale, but it is sufficient to show a good increase in signal.


http://southwell.wdi.co.uk/stats/radio/radio_wpci1_62.72.160.43.html

[kb1_kanobe]

A - B - C

A to B is 13 miles 5.8GHz with PacWireless 29dB SNR 14 to 20 dB
B to C is 13 miles 5.8GHz with PacWireless 29dB SNR 0 to 6 dB

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I am still very puzzled by the high tide effect, I saw that someone else was also seeing it. It is particularly bad when the sea is mirror flat, which it has been over the last few weeks. I see exactly the same effect with 2.4 & 5.8, and for different links. It seems to improve when I use h-pol.



Perhaps you're seeing phasing interference (http://www.solectek.com/techlib/techpapers/whitepapers/wp-fresnel.html) from the surface of the water. As the water gets flatter it's efficiency as a reflector improves and the phasing interference at your antenna gets worse. Likewise if the water is rough it's randomly scattering the reflected signals, decreasing the inteference. Also, check the radiation plots for your particular model of antenna - it's unlikely but there may be a sidelobe that's hitting the water at just the right angle for your range that's contributing to phasing effects.

Have a read of http://www.zytrax.com/tech/wireless/fresnel.htm and then Google for a "fresnel zone calculator" and compare the calculated minimum antenna height to your installed heights.