What is thermal noise??
-
Get involved.
We want your input!
Apply for Membership and join the conversations about everything related to broadcasting.
After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
If you use a disposable or false email address, your registration will be rejected.
After your membership is approved, please take a minute to tell us a little bit about yourself.
https://www.radiodiscussions.com/forums/introduce-yourself.1088/
Thanks in advance and have fun!
RadioDiscussions Administrators
Thermal Noise
- Thread starter eskipper411
- Start date
Every object absorbs and reflects radiation, which it emits as a wide spectrum of wavelengths according to temperature. At absolute zero, the noise becomes zero. It's also associated with noise in electronic circuits, where it has to do with kinetic energy and random movements associated with the molecules of the circuit, again associated with temperature. It is explained by Quantum Physics. That's an oversimplification based on my Physics bacground going back many years.
Thermal noise is inherent in electronic circuits. Do not get it confused with atmospheric phenoma associated with increased summer temperatures (e.g. lighting noise, increased noise due to tropo, etc.).
BTW, best way to consider thermal noise is like boiling a pot of water. As the water heats up it starts to churn and bubble. The hotter it gets the more it bubbles. Think of the bubbles corresponding to noise as a component heats up. And, BTW, in the 'good old days' you used to 'boil off' electrons from the filamaent of a vacuum tube.
BTW, best way to consider thermal noise is like boiling a pot of water. As the water heats up it starts to churn and bubble. The hotter it gets the more it bubbles. Think of the bubbles corresponding to noise as a component heats up. And, BTW, in the 'good old days' you used to 'boil off' electrons from the filamaent of a vacuum tube.
Astromony CCD's used by the professionals are cooled by liquid Nitrogen. For amateur use the preferred method is Thermo-electric coolers. Problems with CCDs is the the thermal noise looks like image and since long exposures are required, lowering the temperature is a requirement. For most radio work, (e.g. NOT trying EME) thermal noise is not an issue.
The electrons "boiled off" a hot filament, or indirectly "boiled off" the cathode in a heater tyoe of a vacuum tube do not
contribute noise anywhere near the level as created by the migration of electrons (and the "holes" migrating in the opposite direction) within semiconductors. Electron mobility is SO much higher in a tube that such noise within
vacuum tube circuits is primarily from carbon resitors.
It is not all bad, in fact, if this random noise did NOT exist, oscillators would not start up without some knd of
triggering pulse.
Sometimes this is called "shot noise".
Good old fashioned bipolar NPN PNP transistors are chock full of this noise,
which is why downconverter LNA heads on satellite antenna have special low noise semiconductors
and amplifiers right at the dish.
In the pictorial below, holes ( nothing where something might have been ) are seen migrating in an orderly fashion
from left to right.
>
>
>
>
>
>
See? If this were not occuring, there would be no ability for the electrons (primary carriers) to flow
within the silicon lattice structure of the semiconductor.
contribute noise anywhere near the level as created by the migration of electrons (and the "holes" migrating in the opposite direction) within semiconductors. Electron mobility is SO much higher in a tube that such noise within
vacuum tube circuits is primarily from carbon resitors.
It is not all bad, in fact, if this random noise did NOT exist, oscillators would not start up without some knd of
triggering pulse.
Sometimes this is called "shot noise".
Good old fashioned bipolar NPN PNP transistors are chock full of this noise,
which is why downconverter LNA heads on satellite antenna have special low noise semiconductors
and amplifiers right at the dish.
In the pictorial below, holes ( nothing where something might have been ) are seen migrating in an orderly fashion
from left to right.
>
>
>
>
>
>
See? If this were not occuring, there would be no ability for the electrons (primary carriers) to flow
within the silicon lattice structure of the semiconductor.
- Status