Calculating performance of outdoor wireless network links

Reading Time: 10 minutes

This article contains information on how to calculate the operating margin of a wireless 802.11 network using a known distance between the two points.

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I wrote this quite a while ago and although the throughput of wireless links has dramatically increased the basic theory still applies. Of course we now have 5GHz available, which is very useful for this application. You should be able to substitute ‘f’ for 5000MHz and the maths will still work.

You can now get a 150mbps PTP link over 15km using equipment that costs £160 for both ends – that’s the entire cost of the system (minus a couple of poles and brackets). Crazy value for money when you think about it. The Ubiquiti NSM5 NanoStation is one such example. The Ubiquiti product range is pretty impressive to say the least. The NSM5 seen below is the big brother of the LOCOM5, which at £125 can still do 10km at the same rate and are around half the size.

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If you are considering an outdoor wireless link, give this article a read so you understand how high above objects you need to mount your shiny new kit!

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JSON Parsing Nagios Script

Reading Time: 2 minutes

Parsing JSON in Bash is never usually the best idea but sometimes it may be necessary or preferred. Here’s a nice easy script which uses the ‘jq’ command to perform JSON parsing in Bash.

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Let’s imagine you have the following JSON which is outputted by a stats gathering process:

{"web_rate":1,"db_rate":2,"php_rate":2}

Parsing that in Bash by writing some regex’s etc is perfecting possible but there’s an infinitely easier way. Welcome to ‘jq’. Let’s see it in action.

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Useful to know Bash parameters

Reading Time: 3 minutes

Even having written many hundreds of Bash scripts over the years I sometimes forget the basic special parameters which are available. For that reason I’ve made this post which is a copy of the page from gnu.org.

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Prevent apcupsd shutting down the OS

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If you have an APC UPS you may not, for whatever reason, want the OS to trigger a shutdown. The ‘apcupsd’ package will call shutdown whenever the battery capacity is reported too low. To prevent this, just edit the following file.

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How to download iplayer content on Linux

Reading Time: 16 minutes

Here is a very simple way to download iPlayer content using a Linux command line tool. This literally downloads the stream and saves it to a file. The best part is, because they’re not DRM protected, you can keep it forever.

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How to resize a VirtualBox disk

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Very quick post on how to resize a VirtualBox virtual disk.

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When using QCOW based disks with Virtual Box there’s no automagic method for resizing the disks. Because of that you first have to convert it. Here’s the commands you need…

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That’s not a server, THIS is a server!

Reading Time: 11 minutes

I thought a wee article on what a server is and why they are expensive compared to your average PC might be interesting. When you hear someone say they have built a server for the house what they usually mean to say is they’ve built a PC and have it running various applications which serves ‘stuff’. A real server is a different beast all together.

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So what makes a server a server? It boils down to the hardware feature set. Sure, you can get low-end servers which are nothing more than a PC in a fancy rack mount chassis, but lets take a look at higher end goodness.

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Apple Macbook Logic Board Schematics

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Following on from my post about ASD versions I’m going to add a couple of board schematics to this post. Anyone who has tried to fix a laptop will know getting a free copy of the schematics is half the battle. I have loads of these but this is a good start.

M87 PS

Included in PDF format are Macbook Air A1304 (MLB M96), Macbook Pro A1278 (K24, 820-2530), Macbook M42B,

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Apple Service Diagnostic Versions

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As I kept finding myself hunting for the correct version of Apple Service Diagnostics I needed for which model of Mac, I’ve included a fairly recent list in this post.

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Here’s the list of Mac models and required ASD versions…

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The nonsense that is ‘Reballing’ dead GPUs

Reading Time: 5 minutes

Reballing GPUs seems to be what all the cool kids are into these days. They make the claim that a dead GPU can be repaired by reballing it. What they aren’t telling you, or don’t realise themselves, is neither did it need reballed nor is it now repaired. Maybe it’s the easy money or maybe they just like the temporary smile on the customer’s face. Lets not beat about the bush though – it’s bollocks and don’t pay for it.

bga

When a high performance chip, such as a GPU, is working hard it heats up. It heats up because it’s drawing high current and the energy dissipates as heat. When it’s off or idle it cools down. Over time this constant change in temperature causes its internal circuitry to start decaying. At high temperatures the tracks (or ‘bumps’) in a flip-chip design BGA chip physically deform and you end up with a dead chip.

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