RTL-SDR Power Consumption

Art ky1k at myfairpoint.net
Mon Feb 6 22:25:47 UTC 2017


Hi Ricardo,

My guess is that it's power supply is a linear type, necessary due to 
the radio frequency hash that would appear as noise if a higher 
efficiency switching supply is used. So, the dongle has to dissipate  
3.3 times 118 milliwatts (389.4milliwatts) instead of 118 milliwatts. 
The point is that 66.6 percent of the 'heat' you feel is not coming from 
the chip itself!

As far as a practical solution, you can build a switching supply and 
build it in the cable run between the punchbox and the unit. You can't 
locate them extremely close to each other if a switching supply is used.

Or, you can locate the linear power supply very close to (but not inside 
of) the enclosure for the chip. Today, linear power supplies can almost 
fit on the head of a pin, provided that the amount of power they 
dissipate is low.

With radio questions related to SDR, check out the softrock mailing list 
on yahoo where you will find many hams, who have extensive exposure to 
radio communication and with SDR.

GL, I hope to get one of these little beauties someday soon, and I hope 
that someone is working on the companion SDR based transmitter, that 
generates an rf output from an audio input....basically doing the 
reverse of what the SDR receiver does.

Regards.

Art

A switching supply could be made outboard from the
On 02/06/2017 12:55 PM, 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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