RTL-SDR Power Consumption

Marcus Müller marcus.mueller at ettus.com
Mon Feb 6 17:55:24 UTC 2017


Hi Ricardo,

I don't think so. Anyway, I'd doubt you can do much but tweaking gains
when it comes to the tuner – and really, the power consumption of that
would be in the milliwatts (datasheet [1] says 118mW typ); and
seriously, in a device that's typically supplied 1.5 V generated using
linear regulators from USB's 5V, I'd say your tweaking will have little
to barely measurable effect.

However, you seem to be more worried about heat than power, actually –
so what's your problem with the heat? At least the datasheet claims a
Noise Figure of about 4.5 dB worst-band, presumably at room temperature.
Going up from 20 °C to 85 °C (max rec. operating temp, assuming your
device doesn't get higher) will increase your noise floor by the
temperature-weighted Boltzmann constant, i.e.  k·𝚫T, so something like
-180 dBm/Hz; I'd have my doubts that this becomes a relevant problem,
even assuming a full noise-equivalent filter bandwidth of 8 MHz (= 66
dBHz -> a noise floor increase by -114 dBm), since we're in a 8-bit
sampling regime (which means the Signal-to-Quantization-Noise-Ratio is
about 50dB (=1.76 dB + 6.02 dB · bits)). Of course reducing temperature
*does* increase SNR, especially in low-signal-power scenarious; however,
the thing you'd probably want the least in that situation is to reduce
the gain of the LNA.

As usual, it's usually easier to help people when you know what exactly
they want to do – I can only guess your heat concern is noise-related.
Maybe it isn't.

In any case, your wording indicates you might want to ask general RF
operation questions, and I'm not 100% sure this mailing list is the
perfect place to do so.

Best regards,

Marcus

[1] https://www.nooelec.com/files/e4000datasheet.pdf

On 02/05/2017 06:54 PM, Ricardo Romanowski wrote:

> Hi,
>
> has anyone yet tried to optimize the rtl drivers towards using less
> energy on the chipset (cpu doesn't matter for my purpose). I just
> noticed that the r820 tuner gets awful hot when used normally or even
> when the device is just inserted into the usb port thus supplied with
> power. I also have multiple E4000 Tuner based dongles, but these do
> seem to heat up pretty well also. My hackrf stays quite cold compared
> to that.
>
> Are there chipsets known for less power consumption (thus less heat)?
> I doubt software could really do much about the chip design, but i'm
> not deep enough into the rtl chipset to judge whether it's more of a
> software- or hardware-issue.
>
> Any ideas on that topic?
>
> Thanks!!
>
>
> Best regards, Ricardo
>
>



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