<div dir="ltr">Just a quick digest below for microdeployments -- some summary excerpts for those who missed both interesting/longer discussions today:<br><div class="gmail_quote"><div dir="ltr"><ul><li>Power-over-Ethernet (PoE) might seem like magic cure (when installing Wi-Fi Access Points across classrooms not having nearby electrical outlets) but PoE is tough to get installed properly, as Tim has discovered!</li><li>Burying Ethernet cabling in a shallow trench between nearby buildings seems rather popular "to the garage" (quite a number of personal experiences are documented online) however this does NOT eliminate the lightning problem. What kind of trenching/equipment mitigates lightning risks and to what degree seems to be open for debate across different web sites (if you don't have El Chapo's tunneling team on your side, avoid these risks using underground fiber or directional wireless/repeaters instead ;)<br></li></ul><br><div><div class="gmail_quote">From: <b class="gmail_sendername">Anish Mangal</b> <span dir="ltr"><<a href="mailto:anishmg@umich.edu" target="_blank">anishmg@umich.edu</a>></span><br>Date: Mon, Jan 11, 2016 at 10:32 PM<br>Subject: Re: [XSCE] RE: [UKids] Ethernet Cable<br>To: xsce-devel <<a href="mailto:xsce-devel@googlegroups.com" target="_blank">xsce-devel@googlegroups.com</a>><br><br><div dir="ltr"><div><div><div>Interesting insight Terry.<br><br></div>FWIW, I did some rough testing of a homemade cantenna a couple of months ago. (Rough, because it was not a perfect Line of Sight)<br><br><a href="http://people.sugarlabs.org/anish/IMG_20150910_222141.jpg" target="_blank">http://people.sugarlabs.org/anish/IMG_20150910_222141.jpg</a><br><br></div>The measured gain over a omni 5dbm antennas was around 7-8 dbm, which would put the overall gain at about 12-13 dbm. Not bad for a tin can antenna made essentially from spare parts :)<br><br></div>In theory, two of these could form a pretty stable link over a kilometre or so. <br></div><div class="gmail_extra"><div><div><br><br>---------- Forwarded message ----------<br>From: <b class="gmail_sendername">T Gillett</b> <span dir="ltr"><<a href="mailto:tgillett@gmail.com" target="_blank">tgillett@gmail.com</a>></span><br>Date: Mon, Jan 11, 2016 at 10:29 PM<br>Subject: Re: [XSCE] RE: [UKids] Ethernet Cable<br>To: xsce-devel <<a href="mailto:xsce-devel@googlegroups.com" target="_blank">xsce-devel@googlegroups.com</a>><br><br><div dir="ltr"><div><div><div><div><div><div>Underground cabling doesn't add a lot of protection against lightning strike as George has related.<br><br></div>One
problem is that when a lightning strike occurs, there are large ground
currents flowing from the point of the strike outwards.<br><br></div>This produces voltage differences between different points on the ground - the further apart, the greater the voltage.<br><br></div><div>If
you stand at one point, you experience no problem. But if you straddle
two points some distance apart, then you are in trouble.<br></div><div><br></div>If
you introduce a copper cable between two distant points, when a strike
occurs you will see a large voltage between the end of that cable and
local ground (to which the equipment is essentially connected). And your
gas arrestors just try to tie it all together and so carry the current
in the copper conductor. <br><br></div>The voltages and currents produced in lightning strikes are truly awe inspiring.<br><br></div>This
is just one mechanism of failure that occurs. A lightning strike is
really like a bomb going off. You can describe what happens in general
terms, but the detail is extremely variable and difficult to predict
with any certainty.<br><br></div>Prevention is generally considered the best strategy.<br></div><br>On Tue, Jan 12, 2016 at 1:18 PM, Adam Holt <span dir="ltr"><<a href="mailto:holt@laptop.org" target="_blank">holt@laptop.org</a>></span> wrote:<br><span>On Mon, Jan 11, 2016 at 10:14 PM, T Gillett <span dir="ltr"><<a href="mailto:tgillett@gmail.com" target="_blank">tgillett@gmail.com</a>></span> wrote:<br></span><span><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div><div><div>Long network cable runs are a magnet for lightning problems, particularly if they are run between buildings.<br></div>And no amount of expensive protection equipment will save you from a nearby strike.<br><br></div>General guideline for lightning prone areas is to keep network cables short as possible and within a single building.<br><br></div>If you need to network to other buildings, consider a wireless technique.<br></div></blockquote><div><br></div></span>Is shallow/quick trenching also viable?<br>Or will rats/worms/frost destroy the cable quasi-annually?<br><div class="gmail_quote"><br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><div><div class="gmail_extra">On Tue, Jan 12, 2016 at 1:08 PM, Anish Mangal <span dir="ltr"><<a href="mailto:anishmg@umich.edu" target="_blank">anishmg@umich.edu</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">fwiw, a simple google search reveals that these are prohibitively priced. <br><a href="http://www.blackbox.com/Store/Detail.aspx/Power-over-Ethernet-Surge-Protector-60-Volt/SP075A" target="_blank">http://www.blackbox.com/Store/Detail.aspx/Power-over-Ethernet-Surge-Protector-60-Volt/SP075A</a><br></div><div class="gmail_extra"><div><div><br><div class="gmail_quote">On Tue, Jan 12, 2016 at 8:36 AM, Anish Mangal <span dir="ltr"><<a href="mailto:anishmg@umich.edu" target="_blank">anishmg@umich.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Perhaps this is slightly offtopic<br><br>Talking to a school a few days ago up in the mountains, they had a lightning strike that knocked out a bunch of electrical equipment. Are there any surge inhibitors for ethernet cables, would using PoE create more of these issues (i.e. the surge inhibitors probably wont work with PoE stuff)? Sure inhibitors are easily available for AC power sockets. <br></div><div class="gmail_extra"><div><div><br><div class="gmail_quote">On Tue, Jan 12, 2016 at 3:10 AM, James Cameron <span dir="ltr"><<a href="mailto:quozl@laptop.org" target="_blank">quozl@laptop.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">PoE can be loads of fun. The products vary considerably; both<br>
injectors, cables, and routers. Most problems can be solved through<br>
measurements, ohms law, and power calculations. Most problems can be<br>
pre-empted by choosing industry best practice equipment, but that<br>
raises costs.<br>
<br>
To avoid all the PoE, there's no substitute for an electrician running<br>
nice thick cables for AC. Because these cables must meet a code, they<br>
are way thicker than they need to be for a router. It depends on<br>
where you want to put your money.<br>
<span><font color="#888888"><br>
--<br>
James Cameron<br>
<a href="http://quozl.netrek.org/" rel="noreferrer" target="_blank">http://quozl.netrek.org/</a><br>
</font></span></blockquote></div><br><br clear="all"><br></div></div><span><font color="#888888">-- <br><div><div dir="ltr"><div>Anish<br></div><div><br><br></div></div></div>
</font></span></div>
</blockquote></div><br><br clear="all"><br></div></div><span><font color="#888888">-- <br><div><div dir="ltr"><div>Anish<br></div><div><br><br></div></div></div>
</font></span></div>
</blockquote></div><br></div><span class="HOEnZb"><font color="#888888">
</font></span></div></div></blockquote></div><span class="HOEnZb"><font color="#888888"><br><br clear="all"><br></font></span></div></div><span class="HOEnZb"><font color="#888888"><span><font color="#888888">-- <br><div><div dir="ltr"><div>Anish<br></div><div><br><br></div></div></div>
</font></span></font></span></div><span class="HOEnZb"><font color="#888888">
</font></span></div><span class="HOEnZb"><font color="#888888"><br><br clear="all"><br>-- <br><div><div dir="ltr">Unsung Heroes of OLPC, interviewed live @ <a href="http://unleashkids.org" target="_blank">http://unleashkids.org</a> !<br></div></div>
</font></span></div></div></div></div>