Modify RTL-SDR Wideband LNA for HackRF TX

Talk about other SDR products like the FunCube, HackRF, BladeRF etc.
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EnumC
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Joined: Fri Oct 23, 2020 8:59 pm

Modify RTL-SDR Wideband LNA for HackRF TX

Post by EnumC » Fri Oct 23, 2020 9:06 pm

Hi everyone, I'm looking for a way to boost the few milliwatts of output power the HackRF can usually provide in order to reach local repeaters for HAM. Is anyone knowledgeable about the wideband LNA RTL-SDR offers and whether it can be modified to be used as a TX Bias-T powered amplifier similar to an LNA4ALL? The output will have low-pass filters to filter out harmonics.

In addition, if anyone knows of any LNA that can boost the output for HF/VHF/UHF frequencies to >=1W, please also comment below.

Thanks,
EnumC

rtlsdrblog
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Re: Modify RTL-SDR Wideband LNA for HackRF TX

Post by rtlsdrblog » Tue Oct 27, 2020 3:53 am

If you have an external bias tee you should be able to easily power it in reverse. Connect the LNA IN port to the HackRF RF port, then the bias tee to the LNA OUT port.

You could also use the external bias tee to take power from the HackRF RF port, and wire it directly to the power pads on the LNA PCB. THen just move the power jumper over so that the LNA takes external power.

EnumC
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Joined: Fri Oct 23, 2020 8:59 pm

Re: Modify RTL-SDR Wideband LNA for HackRF TX

Post by EnumC » Fri Oct 30, 2020 4:17 am

Ah, that makes a lot of sense. I'm not sure why I didn't think of that! Thanks for your help.

snn47
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Joined: Tue Dec 27, 2016 11:00 pm

Re: Modify RTL-SDR Wideband LNA for HackRF TX

Post by snn47 » Fri Oct 30, 2020 9:44 am

There are many prebuilt and modules for amplifier available. The price increased with frequency, bandwidth, amplification and power out.

There are not only only harmonics to consider, but also Out Of Band (OOB) emissions, which can produce interference.
The severity of OOB emissions depends among other factors on the waveform that both HackRF and the amplifier cobined generate. Therefore a band pass filter pass filter may be required to limit the OOB emissions within the required limits.

And of course you need a HAM liscense to be able to transmitt in the HAM bands.

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