Low Frequency Antenna

Discuss commercial and home made antennas.
Posts: 6
Joined: Sun Dec 24, 2017 12:59 pm

Re: Low Frequency Antenna

Post by evelyette » Thu Jan 11, 2018 12:11 am

Thanks, this will be a very interesting read!

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Joined: Sun Mar 24, 2019 3:39 pm

Re: Low Frequency Antenna

Post by BG7YWL » Sun Mar 24, 2019 3:49 pm

I can use rtl-sdr(https://www.ebay.com/itm/273200956857) to see the LF RFID 125KHz signal on sdrsharp, but I can't record the signal using sdrsharp. I think it should be a software setup problem.



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Joined: Sun Apr 26, 2020 9:20 am

Re: Low Frequency Antenna

Post by adameng » Sun Apr 26, 2020 9:49 am

evelyette wrote:
Sun Dec 24, 2017 1:18 pm

I'm a beginner with SDR and signal processing in general, but have been reverse engineering, fuzzing, security checking for more than a decade - I've also visited a highly technical signal processing class in my university, so things shouldn't be too hard for me (in theory). However, we've never actually done anything signal related in real-time with existing gadgets, etc. Therefore, I would like to get myself involved in this in order to expand my horizons. Therefore I've bought the following already:

- HackRF
- Spyverter v2

I would like to record 125kHz frequences, since supposedly my car key transponder works at that frequency. I have the following car key: http://www.digital-kaos.co.uk/forums/sh ... 3373067B-C and the transponder documentation is here: http://www.mouser.com/catalog/specsheet ... 1__C,1.pdf .

Basically, I'm thinking I would do the following:

1. Connect a low-frequency antenna to SpyVerter in order to be able to receive the signal sent from my car key to the car.
2. Connect SpyVerter to HackRF, which will be able to receive frequencies 1kHz to 60 MHz (advertizes here: https://airspy.com/spyverter-r2/)
3. Use HackRF to receive upconverted frequencies: the SpyVerter will upconvert the frequencies to the frequency that HackRF is able to work with, which is 1 MHz to 6 GHz.

Then I would use gnuradio-companion (or any software) to record the signal to analyze it and possibly create my own car key for my car only. This would be an interesting learning and useful thing to do in order to get myself familiarized with all the components that are required to do such a think.

I would like to know what your input is on the challenge and whether I'm missing something that I should address. Also, I was wondering what a good low-frequency antenna, that would enable me to record/transmit 10kHz frequencies would be - I found the following https://www.ebay.com/itm/Mini-Whip-HF-V ... 1576908470, but I'm not sure whether it is any good.

I would be glad if anybody can suggest an antenna that I could connect to SpyVerter v2 in order to receive low-frequencies.

Thank you
hi, would be interested in knowing how you ended of ? i have a similar project.

Posts: 44
Joined: Sat Oct 05, 2019 10:13 pm

Re: Low Frequency Antenna

Post by VE3EAR » Sun Apr 26, 2020 1:32 pm

A multi-turn loop antenna is likely your best bet for receiving LF and VLF frequencies.
A square one of at least 1 metre in size, would be a good starting point. There are
lots of loop building plans on web sites you can check out.

73, Bruce, VE3EAR

Posts: 157
Joined: Sat Jan 14, 2017 11:07 pm

Re: Low Frequency Antenna

Post by hotpaw2 » Tue Apr 28, 2020 4:53 pm

Another possibility for a portable VLF/LF antenna is an old-fashioned loopstick antenna, made by winding a fine wire coil around a ferrite rod. Add a variable capacitor of the appropriate range for a tuned loopstick. That's how those old AM pocket radios worked down to the 100's of kHz without any external or long wire antenna.

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Joined: Fri Oct 09, 2020 12:23 pm

Re: Low Frequency Antenna

Post by lostcowboy » Fri Oct 09, 2020 1:42 pm

Hi, this video may be of interest. https://www.youtube.com/watch?v=CA3XnGyD-SQ

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