[time-nuts] low power, but quiet, oscillators

[jimlux]

On 2/6/17 6:24 PM, Alexander Pummer wrote:
> hi Magnus, how about the effect of that cheap 2,7K on the active device
> if it is bipolar?
>

I wish it were easy to get 2.7k in space.. that's the temperature you're 
radiating to.. At 300K you can radiate a few hundred watts/square meter. 
  When you have finally got down to, say 50K, the radiative heat 
transfer gets pretty small. That T^4 bites you pretty hard.  And on the 
surface of Mars, or Europa, or (worst yet) Venus, that 2.7K radiative 
sink is not so easy to get.  And there's also that 5500K source in the 
sky putting a kW/square meter into you.

But more practically - you see all sorts of cool idea for mesh networks 
and what not.  But they're all "plug the 802.11 node into the 5V wall 
wart" kinds of things.  Just the VCO to make the 2.4GHz probably 
consumes a significant amount of power.

I'd like those mesh nodes to be, say, 10s of mW total power, when 
they're on.  Another problem, of course, is that a superhet receiver 
needs an LO to receive.

So very low power oscillators are of some interest - and low phase noise 
is because, well, this is time nuts.. An RC blocking oscillator isn't as 
interesting.


By the way, some colleagues are building a box to get some Rb atoms down 
to picoKelvins.. Check out Cold Atom Lab.  Push a button and a couple 
seconds later, you have a Bose-Einstein Condensate.



> Greetings
>
> Alex
>
> On 2/6/2017 4:35 PM, Magnus Danielson wrote:
>> Hi,
>>
>> On 02/07/2017 12:36 AM, jimlux wrote:
>>> On 2/6/17 2:37 PM, Bob Camp wrote:
>>>> Hi
>>>>
>>>> One of the most basic reasons for putting out > +20 dbm is that you
>>>> had a spec of -195 dbc / Hz for the noise floor :)
>>>>
>>>> Some of these specs *are* a bit mutually exclusive.
>>>
>>> Sure.. And to be honest, I'm not sure that some of the folks coming up
>>> with paper requirements for these speculative low power transmitters are
>>> aware of that.  They take dBc values from 1 Watt transmitters and assume
>>> you can meet that with your 1 mW transmitter.
>>>
>>>
>>>
>>> Then again couldn't you cool your oscillator.. that gets the T part of
>>> the kT down lower <grin>
>>>
>>> Cool that puppy down to <1K and get 25dB noise improvement, eh?
>>
>> Your 50 ohm termination resistor will be a great source of that noise.
>> For a narrow-band fixed signal you can terminate with whatever
>> reactive network you feel confident with instead. If you match
>> impedance well enough it will work fairly well. Some oscillators have
>> far-out impedances far from 50 Ohm anyway so impedance matching is
>> so-so and most of the noise comes from the termination resistor.
>>
>> Besides, for the deep space stuff you have cheap access to 2.7 K or so
>> anyway, right? :)
>>
>> Cheers,
>> Magnus
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