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.

7 comments

  1. 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.

    73,
    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.

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