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Technical notes - Radio Frequency Spectrum

Trolley Scan products operate on the "tag-talks-first" process which means having a very clean, low interference RF signal which causes minimal interference with other users. Both the Trolleyponder® RFID reader products and the new RFID-radar(tm) use carrier wave signals to provide energy for powering up the passive transponders, and for providing a frequency reference for the communication of data from the transponders to the reader.

The operating frequency of the units can be set to the required frequency for the country of use, lying at some frequency between 860Mhz and 960Mhz depending on the region.

Trolleyponder spectra Trolleyponder spectra
The above two graphs show the same signal with different degrees of magnification. The left hand graph is for a 100kHz wide frequency scan, and the right for a 10kHz wide frequency scan. In each case the vertical scale represents 10dB/division, meaning a ten fold increase in sensitivity. The skirts on the edge of the left graph are 90dB below the peak, that is 1000 million times weaker than the peak signal.

Although we specify an operating bandwidth of 10kHz, most of the energy lies within 2 kHz of the peak value, or all energy greater than 50dB(100 000th) of the peak value.

By way of comparison, the spectra of a reader-talks-first type system such as pushed by EPC etc is shown. These systems generate a lot of interference for other users. The spectra are shown for 1MHz wide and 100kHz wide scans. Trolleyponder spectra Trolleyponder spectra

A white paper explaining the differences and why it is so important to switch RFID to a tag-talks-first type protocol will be available from Trolley Scan at the end of 2006

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