From a post to the MailingList by SamChurchill. This is a little out there but it's an interesting dream.

I have been plugging in numbers to see how far 2.4 Ghz and 5.8 Ghz can go. It appears (to me) that a Seattle-to-Portland LAN Bridge is possible. Two links would be used. They would interconnect on the rim of Mount Saint Helens

Mt St Helens: is located at (46.20 N by 122.18 W) in Washington State Approximately 90 miles from Seattle, WA (a 3 hour drive) Approximately 65 miles from Portland, OR (2 and 1/2 hour drive).

A Seattle-to-Portland LAN Bridge might provide long distance roaming between Seattle Wireless and Personal Telco in Portland and can provide educational/academic/scientific uses as well. Half-circuit blocks of 64Kbps would go half way (to/from the Mountain). A full circuit would connect Seattle to Portland. Circuits might go for $25-$50/month. If we sold 100, 64Kbps one-way "channels", then the monthly revenue would be $2500. The system might cost $40,000.

I have no idea if this is a good idea or even if it's possible. But consider these facts:

1. According to FCC Part 15.407, (http://www.universitypark.org/hope/page10.html), 5.8 GHz UNII-3 wideband digital fixed point-to-point transmitters may use a 30 dBm transmitter with directional antennas with up to 23 dBi gain without any corresponding reduction in transmitter power.

2. Maximum EIRP is 53dBm (200 watts). It's maxed with a 24db (1/4 watt) radio on a 29db dish.
3. A 30dBm transmitter is 1 watt, a 27dBm transmitter is 500mW, and a

24dBm transmitter is 250mW. A 250mW transmitter (24dB) can legally feeda 29 dB gain dish.

Here is a 34 db gain 5.8Ghz dish (that gives us -5 dB compensation for cable loss):

• http://www.tiltek.com/final/html/products.html

• http://www.tiltek.com/final/pdfs/TA-5248M.pdf

How far can we go at 5.8Ghz? Let's do the numbers: (http://www.ydi.com/som.php) We'll figure -83.5dB sensitivity on the radio.

1. OPERATING MARGIN FOR SHOT FROM ST HELENS TO PORTLAND (65 MILES)

http://www.ydi.com/som.php

• Operating Frequency: 5800 MHz
• Distance between Antenna: 65 Miles
• Tx Power: 24dB
• Tx Cable Loss: 5dB
• Tx Antenna Gain: 34dB
• Rx Antenna Gain: 34dB
• Rx Cable Loss: 5dB
• Rx Sensitivity: -83.5dB
• Free Space Loss: 148.1dB
• Rx Signal Level: -66.1
• Theoretical System Operating Margin: 17.4dB

Summary:

• A margin of 17.4dB doesn't seem bad. Now lets to the Mt St Helens to

Seattle link (90 miles):

1. OPERATING MARGIN FOR SHOT FROM ST HELENS TO SEATTLE (90 MILES )

http://www.ydi.com/som.php

• Operating Frequency: 5800 MHz
• Distance between Antenna: 90 Miles
• Tx Power: 24dB
• Tx Cable Loss: 5dB
• Tx Antenna Gain: 34dB
• Rx Antenna Gain: 34dB
• Rx Cable Loss: 5dB
• Rx Sensitivity: -83.5dB
• Free Space Loss: 151 dB
• Rx Signal Level: -66.1dB
• Theoretical System Operating Margin: 14.5dB

Summary:

• A 14.5dB margin is pretty low but the Rx Sensitivity could probably be boosted at least another 5 dB to compensate for the added path loss. In fact, Rx Sensitivity is critical since it and modulation are about the only parameters we can fiddle with.

Background:

The May 18th, 1980, 8:32 am Eruption was triggered by a 5.1 earthquake centered beneath the mountain.

Height of MSH: 9,677 feet before the eruption and 8,363 feet after. Debris Avalanche The largest landslide in recorded history swept down the mountain at 70 to 150 mph

Some areas are covered by as much as 600 feet.

Lateral Blast: Swept out of the north side of MSH at 300 miles per hour creating a 230 square mile fan shaped area of devastation reaching a distance of 17 miles from the crater. With temperatures as high as 660 degrees F and the power of 24 megatons of thermal energy.

URLs:

• St Helen Cam: http://www.fs.fed.us/gpnf/mshnvm/volcanocam/

• USGS http://www.fs.fed.us/gpnf/mshnvm/volcanocam/

• Volcano and Hydrologic Monitoring http://vulcan.wr.usgs.gov/Monitoring/framework.html

• Slide Show: http://vulcan.wr.usgs.gov/Photo/SlideSet/ljt_slideset_old.html

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