[time-nuts] low power, but quiet, oscillators
Magnus Danielson
magnus at rubidium.dyndns.org
Tue Feb 7 00:35:40 UTC 2017
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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