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Saturday, September 23 2017 @ 02:24 AM CDT

Overcoming Distance - Overview

Previous: Location Considerations - Next: Creating Power At Site

Distance from man's power and internet is by far the biggest problem when dealing with true wildlife – the critters just don’t come close enough to civilization for you to use an extension cord to power things or an Ethernet or coaxial cable to get the video/audio back to where you have internet.

Here you see the tower/blind we built out on the Chehalis Estuary to watch the thousands of eagles eat spawned salmon carcasses in Fall. No power or internet for a mile in any direction.

The Chehalis tower is just one example of what we’ve been forced to deal with in some interesting situations. Here are some limits beyond which you need to deal with distance as a true limitation:

A distance needs to be overcome if you reach the limits of a particular technology. Some of these are:

  • Ethernet twisted pair cable – about 500 feet, less in many cases if the equipment on one/both ends is not of good quality
  • Power-over-Ethernet – about 100 feet for some, where the input voltage is less than 48 volts, to the specification’s distance at 48 volts input of 100 meters (328 feet) from where the “injector” is to where the power is used. We’ve seen 400 feet but that’s pushing it.
  • WIFI in urban settings – consumer equipment with standard “whip” antenna – distance in open air with full line of sight can be as much as ¼ mile but if you have walls or shrubs or other impediments to line of sight you probably will get 100 to 200 feet with reasonable reliability. This means you can cover a typical urban yard pretty well but if you have much beyond a ¼ acre spread you’ll have to change to different antennas. Interference from neighbours can be a problem but most places where you’ll encounter wild animals the density of homes is such that it won’t be as bad as some apartment buildings.
  • Wifi – back country – professional equipment with built-in high-gain antennas – line of sight up to as much as 15 miles should not be too much problem. Some systems claim 25 miles but getting that distance can be a real challenge for people without setup equipment that allows precise directional alignment and having an environment without much chance of “rain fade”. Every bit of wood or other water-containing item in between will lower the distance dramatically.
  • Coaxial cable with video signal (and/or audio) on it – depends on the “impedance” of the cable and the core size and insulation type. Common “cablevision” cable (75 ohm impedance) such as RG-59, typically found in local electronics stores, will usually work for “composite video” or audio for distances in the hundreds of feet provided external influences such as radio/TV stations are not too near, and things like ground loops (see section on electrical) are not present. Test it.
    Longer distances – out to 1000 feet, can be done using RG-6 cable – heavier than the RG-59 but also 75 ohm impedance.
    You can also use 50 ohm cable (RG-8 or RG-58) but it is less common.
    The unit shown to the right is a "VDS-2200 Balun" which puts power in one end of coaxial cable (at the house in on Hornby Island in this case) and receives the video and audio from the camera at the other end, up to 1 mile away.
  • 110 volt power cables – how far you can run these depends entirely upon the size of the individual conductors (measured in AWG numbers, typically between 18 and 12, where lower numbers mean larger conductor) and the amount of current the load at the far end draws. For most typical camera installations the load is less than 100 watts total, or about 1 amp. At this current level and allowing for a 10% (11 volts) drop in voltage (about 99 volts out at the end if 110 volts in – most electronics these days will deal with as low as 90-95 volts) then the max resistance can be is 10 ohms. You can look up the resistance (in ohms) of copper wire on the internet from many different sites but remember – the ohm/1000 feet is for one conductor and you need two for the circuit, so the actual distance is ½ as far as you might think – I’ve cut the distances in the following to reflect real length for two conductors
    • 18 gauge – 6.385 ohms/1000 feet – 800+ feet (of 2 conductor)
    • 16 gauge – 4.016 ohms/1000 feet – 1250+ feet
    • 14 gauge – 2.525 ohms/1000 feet – 2000 feet
    • 12 gauge – 1.588 ohms/1000 feet – 3200 feet
  • 12 volt power cables – how far can you run them and not get significant enough loss that the equipment does not run? This again depends on the wire size and the amount of current drawn. The typical “wall wart” power supply will put out about 500 ma (½ amp) If we allow a 1 volt drop (again, approx. 10%) – to 11 volts at the load end, then the maximum resistance of the cable can be 2 ohms.
    • 22 gauge (typical of what such wall warts are wired with) – 16.14 ohms/1000 feet – 60 feet
    • 18 gauge – 6.385 ohms/1000 feet – 150 feet
  • 12 volt power for a whole installation – running a pair of cameras, some lights and a WiFi radio (total load about 48 watts, or 4 amps) – again allowing for a maximum 1 volt drop the max resistance can be ¼ ohm
    • 18 gauge – 6.385 ohms/1000 feet – 20 feet
    • 14 gauge – 2.525 ohms/1000 feet – 50 feet

What the above lengths for 12 volt power should tell you is – convert the 110 to 12 as close to the cameras as possible.

Distant Power

There are two aspects of dealing with power at a distance:

  1. getting “shore” power – that comes from the consumer power grid – to a site some distance away
  2. creating power at a remote site

Shore Power Extension

As you can see from the preamble above, the size of the wire and the voltage (and allowable voltage drop) have a lot to do with how far you can run a cable. If you run the typical 110 volt power out to a site that draws 100 watts, you can run quite a length of cable before the 10% voltage drop might cause problems – about ¾ mile with 12 gauge cable. The only problem is that such cable, made of copper (aluminum requires 2 numbers larger for the same capacity – 10 gauge instead of 12 for example) is expensive.
If you try to run the voltage that the cameras typically run on – 12-24 volts, the problem is worse because the current is up and the allowable resistance total is dependent upon the current draw, not the voltage.

So... rule of thumb is to run the highest voltage practical the farthest you can – then convert to the actual useful voltage at that point. 

If you can't get shore power, then you'll have to generate power at the site - the subject of the next chapter

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