Changing the HackRF's Bias-T Voltage

Talk about other SDR products like the FunCube, HackRF, BladeRF etc.
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RChadwick
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Joined: Wed May 11, 2016 1:36 am

Changing the HackRF's Bias-T Voltage

Post by RChadwick » Sun Sep 29, 2019 3:47 pm

It looks like the antenna Bias voltage for the HackRF is 3.3v at very low current (Q4 and L3 are rated for under 200mA), but all the amplifiers I want to use are 5v, and TX amplifiers often want more current. Does anyone know why 3.3v was chosen for the bias voltage? If I were to replace Q4 and L13 with parts that can handle at least an Amp, and connect the Source of Q4 to 5V through a PTC or fuse, I could get a 5V ~800mA bias. Are there any downsides I'm not seeing?
Thanks!

rtlsdrblog
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Re: Changing the HackRF's Bias-T Voltage

Post by rtlsdrblog » Mon Sep 30, 2019 10:34 am

USB is 5V, so 3.3V was probably chosen to give enough headroom considering USB cable losses etc. We use 4.5V on our V3, but we assume that people will be using a high quality USB cable with little voltage drop in order to get that 4.5V out.

You'll be pushing the limits of the USB if you want to take 800 mA out from the port + the HackRF's power usage. A good USB port might handle that, but some only support 500mA. Your USB cable is also going to need to be good quality.

Might just be easier to use an external bias tee and a plug pack.

RChadwick
Posts: 7
Joined: Wed May 11, 2016 1:36 am

Re: Changing the HackRF's Bias-T Voltage

Post by RChadwick » Mon Sep 30, 2019 11:48 am

Thanks for the response!
That makes sense about the 500mA from the USB port. I modified my HackRF/Portapack to have an internal battery, and used a DC Step-up regulator that can handle 2A.

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