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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