How to fix a broken HackRF

One of the most common reported issues is a significant drop in signal level both in the receiver as well as the transmitter of the HackRF. In this post we will explain the amplifier chain, how to identify this issue and finally how to repair the HackRF.

HackRF has three amplifiers in the receive section. The first is a low noise amplifier (LNA) with fixed gain of 14 dB. The second is an Intermediate Frequency (IF) LNA with gain that varies from 0 to 40 dB. Finally, the baseband amplifier gain can be varied from 0 to 62 dB. On the transmit side, there are two amplifiers. The first is an IF LNA with gain that can be varied from 0 to 47 dB. The second amplifier has a fixed gain of 14 dB.

The following block diagram shows the amplifier chains in the receive and transmit sections of HackRF.

HackRF Receive and Transmit Amplifiers

The first amplifier in the receive and the last amplifier in the transmit sections can be switched in and out of the chain. The designers of HackRF picked the same component MGA-81563 with Gain 14 dB, for both these amplifiers. As it turns out, this amplifier component is very susceptible to damage – even when the maximum input signal level of +13 dBm is not exceeded. This has been reported by a number of users.

So the first question is – how do you know if this amplifier has been damaged? In the video below, adjustments are made to the three different gain settings.

Adjusting LNA Gain and VGA gain affects the input signal level. When the Amp box is checked, the MGA-81563 amplifier is switched into the chain. In the video this is the only setting that results in no change in signal or noise level. The signal level should in fact increase by around 14 dB in the FM band if this amplifier is working correctly.

Testing the HackRF for damage

Similarly if the last amplifier in the transmit chain is not working, there will be a weak signal out of the HackRF as measured on a spectrum analyzer. If you don’t have a spectrum analyzer, you can use an RTL-SDR to view the signal with software like SDR#. Note that if you are plugging the output of the HackRF Transmitter into a RTL-SDR make sure to use an attenuator of 20 dB or higher or you will damage the RTL-SDR.

Once you have determined that the MGA-81563 on either or both receive or transmit paths is damaged, you can repair it.

The schematic below shows the Transmit (TX) and Receive (RX) LNAs.

HackRF Schematic

The picture below shows the location of the LNAs on the PCB.

HackRF Board Layout

Here is an instructional video on how to replace the parts without a hot air gun

How to replace parts without a hot air gun

You will need a soldering iron, solder and solder flux. And if you plan to do a lot of soldering, get yourself a smoke-absorber fan as the solder fumes can get pretty intense.

Summary

In this article we discussed how to fix one of the most common issues with the HackRF – i.e. damage to the first RF LNA. If you have seen other hardware issues with HackRF, let us know and we will discuss them as well.

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2 thoughts on “How to fix a broken HackRF”

  1. Hey

    Thanks for your guide :).
    I wonder why the coupling capacities between switches or LNA are so large. 100nF is a very large capacity for the input path. It may be worth protecting the receiving LNA with two Schottky diodes (pin8 U14 – ground). What do you think about this?

    Greetings!

    Reply
    • You’re very welcome! 100 nF < 1 ohm at 10 MHz. In general as F increases, the impedance decreases to a certain point. I am not sure if an additional Schottky diode would help - I assume you are aware that there's already one at the RF I/O connector.

      Reply

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