LF antenna and ampflication. How?

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stevevaius
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Joined: Thu Feb 16, 2017 6:56 am

LF antenna and ampflication. How?

Post by stevevaius » Fri Dec 01, 2017 8:23 pm

Hi all,
I am new on sub MHz frequencies and have a small project as receiving 100kHz-150kHz band signals and amplify this signal to another receiver. Which devices and setups should I have? I have a budget around 100 USD and need a portable solution. Any help appreciated!

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m_a_x
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Joined: Sat Sep 13, 2014 10:13 pm

Re: LF antenna and ampflication. How?

Post by m_a_x » Sat Dec 02, 2017 9:50 pm

Why would you need a RTL dongle to receive a Rf signal and pass it to another receiver?

stevevaius
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Joined: Thu Feb 16, 2017 6:56 am

Re: LF antenna and ampflication. How?

Post by stevevaius » Tue Dec 05, 2017 9:50 am

I would like to increase range of RFID tags I have (125Khz). I dont know how to achieve it without read and amplify? Any idea?
Thnx

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m_a_x
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Re: LF antenna and ampflication. How?

Post by m_a_x » Wed Dec 06, 2017 2:44 am

Aren't those passive RFID tags with 10cm range?
They do not have batteries but use the RF power transmitted from the reader. You have to go with the reader within the range to power them and get a reply.

stevevaius
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Re: LF antenna and ampflication. How?

Post by stevevaius » Wed Dec 06, 2017 7:30 am

Thanks for reply. Yes I should go within the range of course. But I would like to add a intermediating device to transfer this read signal data from reader to another receiver which will be located lets say 5-9 meters away.

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m_a_x
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Re: LF antenna and ampflication. How?

Post by m_a_x » Thu Dec 07, 2017 9:36 pm

The reader is just a single ic, you cannot pick up the signal from it but you need another transceiver beside that can receive, save in a buffer and trasmit with more power. But then what do you use to receive this more powerfull signal?
Is the standard receiver always listening or just for a fracion of a second after it has sent a request? I have never seen a RFID receiver for passive tags, i suppose that it is not continuosly trasmitting but you need to press a button to send the request and only then it starts receiving. For how long?
Every single sequence has to be tested but at the end I don't think that you can make a small portable device to do this.

W1ABA
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Re: LF antenna and ampflication. How?

Post by W1ABA » Fri Jul 06, 2018 9:03 pm

To answer the OP's question, an RTL-SDR will do the job. BUT-it's a wideband device, susceptible to overload and non linear responses to out of band signals. You'd have to use the mother of all bandpass filters on the antenna input to the RTL-SDR.

You would also need a computer, which is not trivial in terms of power usage and space needed for the whole system.

An RFID tag has a very small and inefficient antenna, which limits it's range severely. Achieving longer ranges at 125 KHz is easier said than done.

As was pointed out by others, build a simple converter with a few chips, it will run on just a few millamps and will provide much better sensitivity, and more importantly....better selectivity.

There are specialty jfets and bipolar transistors that provide very nice noise figures from audio up into the 1 MHz range.

GL

1ABA

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