connecting to public Access Point

Any clue what type of hardware he's using and how much coax between his access point and the 7dBi omni.

Probably. I've only done the fade margin calculations about 20 times in this newsgroup, but once more can't hurt too much. Sigh.

50 watt antenna? That's the maximum power handling capeability of the antenna before it melts.

Ok, let's work the numbers. Due to lack of detail, I'll make some assumptions. Please juggle the numbers to correspond to your reality.

I'll assume your ISP is using a non-amplified access point located fairly close to the omni antenna. That would be about +17dBi xmit power and about 4dB coax and connector loss.

I don't have receive sensitivity numbers for the AP2000+ but do for the DI-624. * 54Mbps OFDM, 10% PER, -68dBm * 48Mbps OFDM, 10% PER, -68dBm * 36Mbps OFDM, 10% PER, -75dBm * 24Mbps OFDM, 10% PER, -79dBm * 18Mbps OFDM, 10% PER, -82dBm * 12Mbps OFDM, 10% PER, -84dBm * 11Mbps CCK, 8% PER, -82dBm * 9Mbps OFDM, 10% PER, -87dBm * 6Mbps OFDM, 10% PER, -88dBm * 5.5Mbps CCK, 8% PER, -85dBm * 2Mbps QPSK, 8% PER, -86dBm * 1Mbps BPSK, 8% PER, -89dBm I can't guess at what speed your ISP has his access point set but my guess is 5.5Mbits/sec 802.11b in order to deal with the largest number of possible clients without undue hassles. That's a receive sensitivity of -85dBm.

I'll assume that in order to get Line-o-Sight, you're willing to install your AP2000+ on the roof near the antenna and power it from PoE. That means fairly low coax cable and connector losses similar to those at the WISP end.

Pluging the quesswork into

starting at the WISP end: TX power = +15dBm TX coax loss = 4dB (3ft LMR-240 plus a mess of connectors) TX ant gain = +7dBi (omni) Distance = 0.25 miles (400 meters) RX ant gain = +14dBi RX coax loss = 4dB (same at other end) RX sens = -85dBm (at 5.5Mbits/sec) The resultant fade margin is 20dB which means it will work. Fade margin is the increase in signal required to communicate above a reference level at wherever the receiver sensitivity is measured with a BER (bit error rate) of about 1 part in 10^5. It can also be translated directly into link reliability.

Reliability Fade Margin 90% 8 dB 99% 18 dB 99.9% 28 dB 99.99% 38 dB 99.999% 48 dB

Note that this assumes no interference, no reflections, clearance in the Fresnel zone, line of sight, and that everything meets specifications. Basic conspiracy theory suggests otherwise. I would be tempted to get just a bit more gain than 14dBi at your end. Pacific Wireless dish antennas come in 15dBi, 19dBi, and 24dBi with prices varying from $30 to $70. I suggest one of these to improve the fade margin, but also to reduce interference pickup from the sides of the pattern.

Good luck.

Depending on the ISPs AP's type and configuration, it is most likely that you will be able to access it with an even lower gain antenna on your AP2000+. Use of a 14dbi yagi will only give you a better margin to work with remembering that the higher the gain of the antenna, the more accurate you need to be in pointing it correctly.

There is no need to add any amplifier at all over that distance considering that you do have LoS. You may not get the full speed that WiFi often runs but coming from an ISP, he probably has some sort of connection speed limiting in place. A good reliable connection at 2Mbs or better should be readily attainable with the equipment you have. Peter

Ever consider putting this on your website (a directory off the main site) and just post the link? Save you a lot of typing this way... just a thought

fundamentalism, fundamentally wrong.