Ik had het reeds aangehaald dat ik niet goed wist of elke LNA gelijk wel niveau kan versterker . Met niveau bedoel ik dan héél kleine niveau's.
Veronderstel dat er geen ruis bestaat : kan ik gelijk welk héél klein signaal versterken of is er ergens een fysische minimumgrens , vooraleer een LNA begint te versterken ?
Omdat ik niemand ken die hier een antwoord op kan geven , heb ik de vraag gesteld op een forum welke zich bezighoudt met microwaves.
Het antwoord is , dat er geen beperking is . Enkel de ruis is de beperkende faktor .
Goed om weten.
Dit is het antwoord.
There is no threshold before the LNA kicks in ...
There is ALWAYS noise. If there was no noise (an impossible situation)
we could have EME (earth, mars, earth) with handheld radios, just by
adding more gain ... but there is always noise. If there was no noise,
from the LNA or anything else then there would be no limits to the
weakest signal that could be received.
There
are different sources of noise ... the sky, the moon itself, the
receiver front end, the mixer ... the purpose of the LNA is to try and
make the dominant source of noise the moon ... then you are hearing
everything that is there. Every stage of the system adds some noise
and amplifies the noise from the stage before ... so yes, the signal is
bigger, but also so is the noise contributed by the LNA itself, the moon
etc ..
Robin Szemeti - G1YFG
en nog een naschrift van Brian GM4DIJ
Er is dus toch , zij het héél ver van ons werkgebied , een zekere limiet
Ok this might not be quite right.
In the absence of other noise, you hit the RF photon noise limit .ie you are limited by the noise on the signal. At 1296MHz the photon energy is 8.59×10^-25 joules. In a 10 Hz bandwidth, at an average of one photon per 1/B (or is it 1/2B) = 0.1 sec the power is 8.59x10^23 mW == -220dBm. 160dBm is about 10^6 RF photons in 0.1 sec
Of course you need more than one photon to make sense of the signal, so that sets the minimum SNR. Then there's local oscillator shot noise as you have to mix down to a frequency where you can get a 10Hz bandwidth.
At light frequencies single photon detection is possible ( it used to be part of my day job), but not at RF since you can't get the other noise sources low enough.
Anyway the answer to your question is that there is no threshold until you hit the quantum limit in the absence of all other noise.
Brian GM4DIJ
--
Brian Howie
In the absence of other noise, you hit the RF photon noise limit .ie you are limited by the noise on the signal. At 1296MHz the photon energy is 8.59×10^-25 joules. In a 10 Hz bandwidth, at an average of one photon per 1/B (or is it 1/2B) = 0.1 sec the power is 8.59x10^23 mW == -220dBm. 160dBm is about 10^6 RF photons in 0.1 sec
Of course you need more than one photon to make sense of the signal, so that sets the minimum SNR. Then there's local oscillator shot noise as you have to mix down to a frequency where you can get a 10Hz bandwidth.
At light frequencies single photon detection is possible ( it used to be part of my day job), but not at RF since you can't get the other noise sources low enough.
Anyway the answer to your question is that there is no threshold until you hit the quantum limit in the absence of all other noise.
Brian GM4DIJ
--
Brian Howie
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