30pW ???

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Hi to all,


the  LIPD (  Low Potential Interference Device ) class licence 2000 allows
the use of deliberate transmitters on a host of bands and at various EIRPs
( radiated powers).

One has me intrigued,  for the band between 3.5 MHz and 3.7 MHz  -   see
page  6 of the PDF.

http://www.comlaw.gov.au/ComLaw/Legislation/LegislativeInstrumentCompilation1.nsf/0/71D36E0C17A40CB3CA2571B80018AF7A /$file/RadcomLIPDClassLic2000.pdf



WTF  is  30pW at 3.6 MHz any good for   ???





.......  Phil



Re: 30pW ???


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http://www.comlaw.gov.au/ComLaw/Legislation/LegislativeInstrumentCompilation1.nsf/0/71D36E0C17A40CB3CA2571B80018AF7A /$file/RadcomLIPDClassLic2000.pdf
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I wonder how they derive these numbers?
Even RFID transmitters operating at similarly low frequencies have a maximum
100pW EIRP (item 30).

Re: 30pW ???



"swanny"
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http://www.comlaw.gov.au/ComLaw/Legislation/LegislativeInstrumentCompilation1.nsf/0/71D36E0C17A40CB3CA2571B80018AF7A /$file/RadcomLIPDClassLic2000.pdf
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** That might be the application  -   RFID badges.

Most are just a coil and a tiny diode used to generate harmonics of the
drive signal.

Makes them technically transmitters with a few pWs power level.




.......   Phil






Re: 30pW ???


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http://www.comlaw.gov.au/ComLaw/Legislation/LegislativeInstrumentCompilation1.nsf/0/71D36E0C17A40CB3CA2571B80018AF7A /$file/RadcomLIPDClassLic2000.pdf
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Good point. Those anti-shoplifting and library book passive stick-on RFID tags
would fit your description.
I'm not sure what frequency they operate at, but the detector coils you walk
through at the entrance/exit seem to be quite large.

Re: 30pW ???



"swanny"
 Phil Allison wrote:
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 **  Look about right size for an AM band frame antenna  -   don't  they
just  ?





......   Phil



Re: 30pW ???


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Right, but..

I believe they're large because they use near-field coupling,
1/d^3 instead of 1/d^2 as with EM transmissions. The receive
antenna in the book is tiny, so it's compensated by having a
very large reader antenna. Probably 125KHz...

Re: 30pW ???



"Clifford Heath"
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** Yep  -   there is very little EM energy delivered to the far field from
such a set up.


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** I fancy it is a tad higher than that.

Must take an AM radio with me on my next trip to Franklins
or K-Mart  ........




.......   Phil



Re: 30pW ???


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    From http://www.easitag.com.au/whatIsSourceTagging.aspx ....

What is RF EAS?
Radio Frequency (RF) Electronic Article Surveillance (EAS) is a proven
and successful concept where electronic sensors alarm when unauthorized
RF tagged merchandise is being removed from EAS retail environment.

What is RF EAS Source Tagging?
When merchandise is secured using RF EAS security tags (usually in the
form of a label) at the point of manufacture.  The RF EAS tag can be
positioned directly onto the merchandise or concealed within or on the
packaging.

How does RF EAS work?
RF EAS sensors are located at all the customer exit points. The sensors
contain either a transmitter or a receiver.  The transmitter and
receivers are tuned to 8.2 MHz as are the RF EAS tags and labels.  When
a live tag passes through the sensors it activates a signal to the
receiver, which in turn alarms the system.


    A selection of tags are at: http://www.bestsecurity.com.au/eas.html


    It looks like one of the more common frequencies used in Aust is
8.2MHz. The printed coil/antenna in paper tags I've removed and examined
(after leaving the store, in case you were wondering!) look like they'd
have enough turns to resonate in that part of the band.


Bob











Re: 30pW ???


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Lots of airport luggage gets tagged with these now, a clear adhesive
label with the antenna visible. They can now lose your luggage with
the utmost efficiency.

Dave.


Re: 30pW ???



"Bob Parker"
 Phil Allison

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** So come under Item 30 in the list of LIPDs with 100pW output ??

    Or maybe have no RF output at all   ......




.......  Phil



Re: 30pW ???


On Tue, 11 Sep 2007 21:14:54 +1000, Bob Parker

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The most common systems use 58khz and 8.2mhz as suggested. I have also
played with some 125khz systems. The lower frequencies are supposed to
be less susceptible to being fooled with metallic foil, but I can
guarantee you that the quickest way to destroy the tags is to drag
your feet around a store and hit them with a static discharge.


Re: 30pW ???


Probably EAS tags

Check here
http://en.wikipedia.org/wiki/Electronic_article_surveillance

It's a Tx Rx system  where a tag in the field helps the Tx reach the Rx and
sound an alarm

My understanding is  - if an emitter is only transmitting in the near field
(more magnetic than electro-magnetic field)  then it is not classes and an
intentional radiator and not really a transmitter.


Joe


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