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.
WTF is 30pW at 3.6 MHz any good for ???
....... Phil
I wonder how they derive these numbers? Even RFID transmitters operating at similarly low frequencies have a maximum
100pW EIRP (item 30)."swanny"
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
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.
** Look about right size for an AM band frame antenna - don't they just ?
...... Phil
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..."Clifford Heath"
** Yep - there is very little EM energy delivered to the far field from such a set up. ** 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
From
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:
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
Probably EAS tags
Check here
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
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.
"Bob Parker" Phil Allison
** So come under Item 30 in the list of LIPDs with 100pW output ??Or maybe have no RF output at all ......
....... Phil
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.
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