[Hackrf-dev] HackRF Questions

[Martin Smith]

On 31/03/2016 14:04, O.T. Powell wrote:
> How do I ask questions on the mailing list?  Would that be a mailing list
> submission?
>
> I'm wanting to know,
>
> I just purchased a Ham It Up Converter to use with the HackRF.
>
> Additionally, I have a LNB, and an LNA.   Could I run all three of these at
> the same time?
As long as no signal from DC to 6GHz after amplification exceeds -5dBm.
https://github.com/mossmann/hackrf/wiki/HackRF-One#receive-power
The normal reason use use a LNA is to add a little bit more
amplification (to the noise as well as the signal of interest) to
compensate for the losses due to the signal passing through a long
length of coax cable.

The ham-it-up does not have an amplifier so it will only add a slight
amount of attenuation from it's two filters, the LPF on its input and
the IF BPF on its output:
https://github.com/opendous/Upconverter1v3
Any signal that you loose from filters you will more than gain from by
what they are blocking. Just make sure then your antenna is optimal for
HF/MF frequencies.

If you are using a LNB just be careful to isolate any power injection
required for its operation, from entering the HackRF. If you are using
an 22kHz LNB local oscillator selector tone, normally about 0.65 Volts
peak-to-peak sine-wave (~0dB), you would be safer if you added 6dB of
attenuation.

> The HackRF has a LNA already incorporated, correct?  So would I see any
> benefit of running another one?
Most users leave the LNA in their HackRF off because it operates from DC
to 6GHz and is in front of all filtering. Without checking that there
are no strong signals nearby within the entire operating range you could
damage your unit. I suspect it is there for people living in RF
wastelands more so that people living in the RF junkyards of most cities.

The problem with adding gain is that you amplify the signals that you
want and also the noise that you do not by an equal amount. And if you
add too much gain you end up distorting the signals that you actually
wanted to see. You will get better results from adding a filter at or
near your antenna with a tiny amount of gain, than by adding more gain
at your receiver.
> Also, what's the best way to amplify a transmitted signal?
>
Please do not. First maybe get a ham license and, as part of the
process, learn all that would need to know before trying to turn up your
TX power.
>
>
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