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THAR BE KIWI |
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I was asked by the New Zealand Department of Conservation (DOC) to look at ways of improving radio direction finding (RDF) for transmitters on kiwis. The problem is mostly when close ( within 20 metres of the bird).
My initial suggestions that DOC paint the kiwis day glo orange, or set fire to the forest and catch them when they ran out, didn’t really meet with the enthusiastic response I had expected.
EQUIPMENT Doc is using 99 channel vhf receivers (RX) and 3 element yagis (driven element is a folded dipole). Antenna is collapsible. There is also an attenuator which appears to be an in-line resistor that inserts between antenna and RX.
The transmitter (TX) is a small (about 30mm) brown thingy that is quite remarkable. It transmits for about 12 months with a long range, and will even indicate if it hasn’t moved for 24 hours (I’m thinking about putting these on some of my staff in my factory—I often don’t know where some are, and others don’t seem to move for days)
HOW TO USE THE GEAR. As is often the case, the equipment is great but misses the boat because of inadequate instruction. With the standard gear you should get within 10 metres of the TX—probably a lot less.
What happens is that when you are getting close (under 100m), the TX becomes too strong for the RX and you can’t tell whether it’s louder in any direction. Us technical nerds call this “overloading”. Both the RX and your own ears can’t differentiate.
The solution is simple, don’t bother using the attenuator, change the RX to the next channel
For example, your kiwi TX is on channel 57—switch to Channel 56, keep switching further away from 57 until you can just hear the TX , when you get within a few metres you will probably hear the TX way down on channel 10 and you will still be able to DF it.
Some points to remember 1. Are there other kiwis about—don’t use their channel are you’ll spend all day chasing them both. 2. Keep swinging the antenna right around. 3. Use headphones when you get close 4. Triangulate—move well to one side and get another bearing—where it crosses the first bearing will be the kiwi. 5. Turn antenna on it’s side when trying to see whether the TX is up or downhill 6. The channels run from 1 to 99 like FM radios—channel 1 isn’t next to channel 99 7. With practice you will learn that when you can hear the TX 4 channels away, it is probably within 10m etc—although this changes with vegetation and TX battery age. 8. Practice (see further down the page)
PRACTICE Learn the technique before you try it on a real kiwi. Get together with someone and play hide and seek using a kiwi TX (but remember where you put it)
Those that never played “hide and seek” are referred to my course (Hide and Seek 101—ISO 9002)to be held in Maui, Hawaii (USD$7000 not including lunch)- sorry, I thought I was dealing with that other Government Department.
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Where be Kiwi ?? |
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Graeme Hunt 30 Grand Vue Rd Rotorua New Zealand Ph 07 3491581 Fax 07 3491681
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