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

Alexander Pummer alexpcs at ieee.org
Mon Feb 6 21:24:12 EST 2017


hi Magnus, how about the effect of that cheap 2,7K on the active device 
if it is bipolar?

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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