I am quite new to RFID, so please bear with me if this is a stupid question. I am trying to build an extension cable to relay an RFID signal (125 kHz) to various distances (2, 5 and 10 meters). I am using two identical antennas at the ends of a 75-ohm coax cable, and I put two identical baluns between the antennas and the cable ends. By using HackRF coupled with HamItUp, I was able to verify that the signal from the RFID emitter does seem to reach the antenna at the end of the cable with seemingly identical waveform and amplitudes. However, when the passive element of the RFID emitter is put in the proximity of the antenna, it is not recognized. I also tried removing one balun from either side of the cable, but it didn't help. Where should I start investigating the problem? Do I need an amplifier? If so, how should I determine its features?
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This is a good question for an engineer, so I spoke with James Heurich at RFID Inc., who had some good suggestions. First of all, if you increase or decrease the antenna cable length of an LF reader, you have detuned the antenna. So 125 KHz could be transmitting at 115 or 135 KHz. This is all dependent on the source of the reader and antenna. Heurich notes that increasing cable length from 12 feet to 30 feet of cabling tends to result in a 15 percent loss of read range. However, if your reader is not designed to work with an external antenna, or if you’re going from a 2-foot to a 33-foot cable, that can result in dramatic loss, or even a zero read range. A lot will depend too on the power of the reader.
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