RTL-SDR Power Consumption

Ricardo Romanowski spam at rocketri.de
Mon Feb 6 21:39:16 UTC 2017

Hi Marcus,

thanks for the Information!

Though it might seem (and the temperature rise of ~40 degrees (i 
measured) between no power supply and a active chipset propably has 
*some* impact on the signal recieved) heat is not my main concern.

My application is a raspberry zero with a oled screen and a battery 
attached that's a portable and slim sdr scanner. The raspberry performs 
superb battery-lifetime-wise (7 hours of idle/4 hours under 100% cpu 
load on a 1Ah single cell lipo) and i'm looking for the longest battery 
life that i can possibly archieve (as well as smallest size).

I've continued searching for info on that topic after i sent the mail 
and found that there are indeed big differences between chipsets: 
https://www.reddit.com/r/RTLSDR/comments/2e9u7v/power_consuption/ which 
means that the E4000 uses (very) roughly 1/3rd of the energy of a R820T 
chipset. To bring that into some relation:
for the raspberry to last 4 hours under full load on a 1000mAh battery 
(voltage regulator losses included) it propably draws ~250mA. Attaching 
a 300mA usb dongle would  propably mean that i would get 1.8 hours of 
lifetime, while IF the E4000 only uses 110mA i'd get 2.7 hours of 
lifetime. Thats a significant difference (for me).

So much for describing my application and concerns a little further. All 
the numbers are unproven so far (except for the 7h /4h lifetime of the 
zero, i did measure that), meaning that i need to experiment a little 
further and examine some chipsets power-consumption-vise myself.. As a 
sidenote, the battery has nominal 1Ah on 3.2V (lipo) meaning that after 
upconverting the voltage to 5V though a regulator (+loss) for that 
lifetime the pi zero propably draws even less current than 250mAh, thus 
increasing the impact of the power consumption of the rtl-sdr device for 
my battery life even further.

Thank you so much for the description of temp-increase vs. signal 
quality - in order to understand it completely i propably have to dive a 
little deeper into general RF as you suggested.

Maybe somebody is able to confirm the numbers for current draw, or even 
point me towards more energy-efficient rtl-sdr hardware (with a small 
form factor)

Best regards, Ricardo

On 06.02.2017 18:55, Marcus Müller wrote:
> 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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