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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