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Ferret Finders
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30-01-2013, 09:31 AM
The other day I was asked to solder a pre-set pot. into one of these. The receiver looked like an AM(MW) Radio c/w Ferrite rod aerial, and it set me wondering what frequencies are used for these devices(didn't think to try and measure it at the time!) Does anyone know?
30-01-2013, 02:18 PM
I remember an article many years ago (80s I think) from ETI magazine (whatever happened to that?) involving the design and use of a device called the Troglodyte. The unit was a two piece affair and was designed for mapping out cave structures underground. The caving team would have a transmitter unit housed in an ammo tin whilst the above ground team would map the underground teams location by the strength of the signals being transmitted. What struck me about the design was the frequency used, quoted as VLF bands, so I suspect that the ferret finder is working on those same frequencies. Interesting to note that the passage of time has shrunk the contents of an ammo tin down to a device small enough for a ferret to wear, a good example of progress.
30-01-2013, 03:27 PM
These are also known as Terrier Finders, and as the owner of a Russell/Border Terrier Cross, I know from bad experiences the aggravation of trying to find, then dig out, a terrier...
They work at 457khz, which is the international standard for radio detection in applications such as avalanche beacons etc. Range is about 20mtrs - ALL ferret/terrier finder applications work at this frequency be it analogue or digital (e.g. the Deben range). I would have thought that you could build one as a modulated AM xmtr with some ease and use a directional aerial on the locator... See https://www.bellmanandflint.co.uk/ and http://www.deben.com/terrier-finder.html etc. About 200+ quid to buy a whole system (collar on own is about 80 quid), much less to make yourself... plenty of comments out there if you Google "diy avalanche beacon"... I have a border RF fence round our property to keep both our dogs inside the boundaries - the dogs have a collar that vibrates when the are 2mtrs from the fence, then lets them know rather more firmly (small shock) when they get within 1mtr - after the first couple of times they won't even go near the fence, even if their collar battery is flat  p.s. These collars are legal in England & Scotland, but not Wales. p.p.s. Not approved anywhere for use on children...HTH
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30-01-2013, 05:49 PM
The Ferret Finder in which I re-soldered a loose pre-set pot. is actually an obsolete Deben model. I have viewed their website out of curiosity. I thought these worked on a medium frequency because of the components used(specially the Ferrite Aerial ) but am surprised 457kHz is used, given that the I.F. in many AM radios is 455kHz.
30-01-2013, 06:31 PM
I was also surprised at the frequency quoted. Through-the-Earth communications is usually at ULF, 300Hz to 300kHz. I suppose if the target is at shallow depth then higher frequencies can be used. I would think that 455kHz to 470kHz is pretty contaminated anyway.
I think this will be OTT, especially the Power http://minesite.wpengine.com/application...nications/ Alan |
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