Using a HackRF to Transmit To a Local Repeater

Over on YouTube Tech Minds has uploaded a new video where he shows how he can use his HackRF SDR with the SDRAngel software to easily transmit voice to a local ham radio repeater. If you are unfamiliar with ham radio, a ham repeater is simply a radio station that receives voice or other signals on a certain ham radio frequency, and re-transmits the signal with stronger power on another frequency. This allows communications to be receivable over a much larger distance.

SDRAngel is a very nice piece of SDR software that has controls for TX capable SDR's like the HackRF. In the video Tech Minds shows the HackRF being used as a transmitter, with it transmitting to a repeater at 145.137 MHz. An RTL-SDR is then used to listen to the repeater output at 145.737 MHz. With this set up he is able to contact a friend via the repeater easily.

It doesn't appear that Tech Minds is using any sort of external amplifier, so this shows that the HackRF is powerful enough to hit local repeaters just by itself.

Transmitting With A HackRF One Via My Local Ham Radio Repeater


  1. Mark Jones

    So… If it has a bandwidth of up to 20 MHz, why can’t he receive with the HackRF over a bandwidth difference of .6 MHz?

  2. Jake Brodsky

    My primary concern is that the HACKRF One put a clean signal on the air. If I were doing this experiment, I would construct a band-pass filter to ensure that any harmonics or other spurious signals are reasonably controlled. The video made no mention of any filter or prior testing with a spectrum analyzer.

    I don’t care if the receiver gets crunched. That’s your problem. I care if the transmitter puts garbage on the air. That’s EVERYONE’s problem.

    Jake Brodsky, AB3A

    • AD5NL

      I have a bunch of the mini-circuits low pass filters with SMA connectors for my limesdr. They are probably not the platonic ideal of harmonic suppression (I am pretty sure though that they should give 20 or 30 db out-of-band suppression at least) but they can be bough online for cheap and even a trained monkey could use them.

      It might add $20 (used) to your project but at least I can look the FCC straight in the eye and say “I tried” to be compliant.

      Of course once could also probably build a super-great bandpass filter themselves with some capacitors and a little magnet wire.

      • Jake Brodsky

        The point I am making is that there are standards that nearly all governments set regarding how well a device suppresses out of band spurious emissions. I suspect that there is a great deal more coming out of that HackRF One transmitter connector than just the desired signal and it is probably not even in-band. It is incumbent upon any amateur licensee to determine that the transmitter was either designed and certified to a specific standard, or that it has been tested and known to meet that standard. The HackRF One was NOT certified to any standard for the transmitter.

        Chances are that it won’t interfere with anything critical, but you never know. All it takes is one airliner having to execute missed approach procedures and the authorities will come looking for you. It has happened before due to faulty outdoor amplified TV antennas.

        If anyone here is going to play with the HackRF One’s transmitter feature on the air, please put a filter after it. This applies regardless of whether you think you’re radiating on an unlicensed frequency or are operating with a proper license.

    • Shhh Whosaidthat

      to jake, I wouldn’t put to much stock in his setup, the repeater could be his neighbors house lol and I didn’t hear a mention of antenna configuration and shielding, I doubt he was only. 5mw and getting 1:1 SWR , but anyway don’t buy a hackrf for Amiture Radio it just doesn’t make sense. If your into testing and experimenting in the in the RF then sure, use gnuradio or python and start designing some cool protocols and filters then ya grab a hackrf, but then again for the money I would move to something post circa 2014 lol. As always Dont forget to spam the hell out of the control operator, jam the NAV band, begin all transmissions with the word Priority to ur NCS, say CQ a lot, try to transmit in the Ametur Extra Band at all times, Make sure your radiated power is way up on a satellite uplink, and Finaly Most Important Place your antennas on your lawn with at least 100watts PEP at the antenna and hang a sign that says “Touch Me For Candy”…

      Peace and Long Life.

    • Jerry

      The fool thing only transmits 10mw at best, I doubt if any IMD components, spurs, or harmonics are going to be strong enough to interfere with anything. I’ve got a HackRF One coming in the mail, and yeah, I’ll look at the output with my spectrum analyzer before I connect it to an antenna. If I find any +40 dbm spurs or harmonics, I’ll let you know. But I do intend to do some experiments with ultra QRP transmitting.. 🙂

        • Anonymous

          Wondering about that too. I know that some folks have used HackRF with small amps and filters to do QRP experiments for fun. I bought one (a cheap clone) for a specific receive only application, and it worked well. But every time that I open the drawer that it now lives in, I hear it calling me to do more with it.

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