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Hi,

I was just wondering if anyone has ever seen a white paper/how-to/guide on installing/using leaky coax for a 2.4Ghz WLAN installation?

Thanks,

Trevor Textor

I haven't seen a guide.

I've seen references to people using it. Would it be legal in the U.S. if nobody has certified it with an AP? I think you might have an issue with maximum RF exposure compliance, since it is a very large "antenna". Not that RF levels would be so high, but because it is non-standard, you might be in the position of measuring the fields.

With the usual 100 mW AP output, levels are pretty low along the coax. Range for good signals is only a couple meters from the coax as you get further from the AP. Which would be fine in some environments.

Another issue is that if there is interference generated anywhere along the line, it wouldn't remain localized interference.

With the usual 100 mW AP output, levels are pretty low along the coax. Range for good signals is only a couple meters from the coax as you get further from the AP.

Charles. Actually, if the leaky coax is terminated properly, the power level from one end to the other should be the same (low SWR). Therefore, the distance you can be from the leaky coax should be the same whether you're close to the AP or the terminator.

(and I won't be back)!

-Tim

Thanks for your note, Tim. I may have given a mistaken impression about how much the signal varied along leaky coax by wording my earlier reply poorly.

You only have high signal levels around 2-4 meters from the cable, anywhere.

I thought I remembered some additional loss further along. Normally a few dB isn't very significant, but due to the low levels several meters from the cable, it might be.

I did a quick experiment with one type of radiating cable. I'm not claiming high accuracy, since I was using a standard client card (Ubiquiti SRC), and all the client cards I've seen can have a range of RSSI values sitting still with the same AP power output, with nothing moving.

The cable was 60 feet of Radiax slotted RXP4-1 1/2"

http://www.andrew.com/search/BN_RXP4-1.aspx

Power at the AP end was 9.2 dBm on 2437 MHz, and below 5 dBm at the other end. The cable was terminated with a 50 ohm dummy load. This coax is shown as having a loss of 6.7 dB per 100 feet.

Measured signals at 5 feet from the cable were around -62 dBm in the first 20 feet from the AP, and about -65 in the last 10 feet. If this measurement is pretty close, it should mean 5-7 dB lower signal at 100 feet along this cable.

There seems to be some published support for lower signal levels with increasing distance, if you look at Figure 2, "Relationship between coupling loss and longitudinal loss"
in
http://mrtmag.com/mag/radio_leaky_cables_good/
'LEAKY' CABLES ARE A GOOD THING
by Jay M. Jacobsmeyer, P.E.

Charles Preston
http://www.comsec-wireless.net