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I would like to transmit data at 125 kHz frequency. I'm wondering what is the realistical transmission distance that can be achieved with this antenna:

It's a rectangle shaped 9x12cm coil antenna. Transmitter frequency: 125kHz

Inductance: 1.04mH

Resistance: 15ohms

(https://www.electrokit.com/en/product/rfid-antenna-9x12cm-125khz/)

In the description it says 'long-range'. I understand that LF transmissions usually take place in centimeter/millimeter measured distances, so I'm not sure what is meant by 'long-range'.

I'll be using Arduino to drive the antenna for now, and I'm wondering how far I can transmit signal/data and what can be done to increase the LF transmission distance?

I’m looking to transmit at about 1 meter range*

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    \$\begingroup\$ Please consider editing a description of the problem you are trying to solve by doing this into your question. What range do you need? Why do you want to use VLF? What sort of modulation scheme will be used? Will there by any validity, redundancy or retry mechanism? \$\endgroup\$
    – Chris Stratton
    Commented Aug 30, 2020 at 18:57
  • \$\begingroup\$ A CB radio managed UK to USA by bouncing off the clouds or similar - freak conditions though... \$\endgroup\$
    – Solar Mike
    Commented Aug 30, 2020 at 19:23
  • \$\begingroup\$ I have not seen this type of antenna used for transmission. I believe the efficiency is low, so you have to compensate by amplifying the input signal. It can make a good receive antenna, though. \$\endgroup\$
    – user57037
    Commented Aug 30, 2020 at 20:25
  • \$\begingroup\$ @Solar Mike The ionosphere might have something to do with it. At 27 MHz, low power signals will get around the globe at sunspot maxima. \$\endgroup\$
    – Chu
    Commented Aug 31, 2020 at 0:48
  • \$\begingroup\$ @mkeith Hmm. I have considered using TLE2301 to somehow amplify the input signal. Do you think it’s a good idea, and if I implement it what range do you think is possible? I’m aiming for about 1 meter transmission range \$\endgroup\$
    – Medita Inc.
    Commented Aug 31, 2020 at 10:27

2 Answers 2

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It's a 125 kHz transmit loop antenna for RFID applications which would need a typical range of around 100 mm that could go up to 300 mm or even 2000 mm in industrial applications.

When used for other applications, the range would depend on the transmitter output power and on how well the antenna could be matched to the transmitter output.

The maximum signal would be in the 'end on' directions of the loop.

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  • \$\begingroup\$ I’m looking to transmit at about 1 meter range. I’ve considered using something like TLE2301 to amplify the signal. What do you think? \$\endgroup\$
    – Medita Inc.
    Commented Aug 31, 2020 at 10:30
  • \$\begingroup\$ You may do that with the antenna series-tuned to resonance at 125 kHz (in case it isn't already, on account of its winding capacitance). \$\endgroup\$
    – vu2nan
    Commented Aug 31, 2020 at 14:33
  • \$\begingroup\$ Can I tune this antenna using capacitors and achieve better range using TLE2301? \$\endgroup\$
    – Medita Inc.
    Commented Sep 1, 2020 at 14:27
  • \$\begingroup\$ The antenna may work, as is, with a specific RFID reader. For your own setup you would need to carry out some trials using a variable capacitor in series with the loop. A (500 + 500) pf variable capacitor in parallel with a fixed 500 pf capacitor would give a capacitance range of 500 to 1500 pf. \$\endgroup\$
    – vu2nan
    Commented Sep 1, 2020 at 16:33
  • \$\begingroup\$ Thanks for advice. I’ll try experimenting \$\endgroup\$
    – Medita Inc.
    Commented Sep 2, 2020 at 11:06
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Although this is labeled an "antenna", it's really an RFID coil, like you see in those pedestals surrounding a store entrance. RFID systems operate in the "near field" which extends at most a few coil diameters away. It will not radiate efficiently enough to send a signal to a distant location at the 125 kHz frequency. It takes something more like this :)

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  • \$\begingroup\$ What if I amplify the input signal using something like TLE2301? I’m aiming for about 1 meter transmission range. \$\endgroup\$
    – Medita Inc.
    Commented Aug 31, 2020 at 10:29

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