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Topic: Receiver's Noice Input =K*T*BWeq ? (Read 1 time) previous topic - next topic

Fovakis

Hi!

My transmitter send a signal with BWsignal=17KHz..

The receiver has an antenna with BWantenna=30MHz...

I work in a laboratory so T~300k.What is the Input Noice to receiver?

P=KTBWeq=>-174(dBm/Hz) + 10logBWeq

BWeq? what is this?

What i will see in my S.A?it depends from the SPAN,right?

pito

#1
Jun 02, 2013, 04:47 pm Last Edit: Jun 02, 2013, 05:00 pm by pito Reason: 1
That is related to the thermal noise floor. If the input of your receiver is broadbanded and the antenna has BW=30Mhz, then you have calculate with BW=30MHz :)
If the receiver has BW=100kHz, then calculate with 100kHz.
BWeq is related to data rate in a channel, for example BWeq = 4 * Rb, where Rb is the data rate (for example 16kbits/sec)

KeithRB

Unless you have a very good spectrum analyzer, you probably won't see anything. The noise figure of a spectrum analyzer is usually pretty high. You probably need a low noise pre-amp to measure the actual noise figure. IF you really want to measure it, you will probably need an excess noise diode and use the Y-factors to calculate it.

Fovakis

ok... what is the noiceInput finally? with BW=30MHz of antenna or BWsignal=17khz what is the calculations?

KeithRB


mauried

What are you trying to measure .
Measuring the noise input to a receiver isnt a very useful measurement , unless you know
the IF bandwidth of the receiver, as this tells you the signal to noise ratio of the signal at the
receivers detector.
This is generally what most people need to know, as it defines the minimum signal input to the receiver
thats needed to decode a wanted type of modulation.

Docedison

#6
Jun 03, 2013, 07:06 am Last Edit: Jun 03, 2013, 07:13 am by Docedison Reason: 1
BWeq means BandWidth and somehow I think you are missing a part of that equation, the part that deals with impedances because as I remember in order to calculate voltage or current noise requires an impedance.
Or some means of normalizing the measurement, usually to 50 ohms but it can be any simple or complex impedance.
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MarkT

The "receiver noise bandwidth" is the figure that you need - the equivalent brick-wall bandpass bandwidth of the
receiver's response.   You'll get noise from the input stage(s) of the receiver and from the air (interference from artificial
and natural sources, and ultimately the 2.7K background radiation from space).  Also resistive losses in any cable between receiver
and antenna will introduce noise too (more at higher RF frequencies).  Only the resistive elements of the losses will
be at 300 kelvin.  Interference may dominate if you are in a city, for instance.

Point a good antenna straight up and you'll often get a noise temperature well below 300K, but also interference from
satellites, the sun, Jupiter (again RF frequency dependent).

Given the antenna bandwidth is so wide it implies you are well into the UHF bands, I think this means less interference
in general, so thermal noise will dominate.

And you should use natural logs, not base 10 for that equation....   k T ln(bw)
[ I won't respond to messages, use the forum please ]

Fovakis

Thanks very much all of you my friends. I will read and i will back again in some days.

Thanks

MarkT

Sorry, got completely confused there, its k T bw, the ln term comes in signal to noise ratio.
[ I won't respond to messages, use the forum please ]

Fovakis


BWeq means BandWidth and somehow I think you are missing a part of that equation, the part that deals with impedances because as I remember in order to calculate voltage or current noise requires an impedance.
Or some means of normalizing the measurement, usually to 50 ohms but it can be any simple or complex impedance.


Hey this is my experiments. Transmitter and receiver are in a lab both and they have distance between them 3 to 5 meters....
http://i1284.photobucket.com/albums/a578/fovos1/P6131098_zps37d09fcd.jpg

Fovakis


The "receiver noise bandwidth" is the figure that you need - the equivalent brick-wall bandpass bandwidth of the
receiver's response.   You'll get noise from the input stage(s) of the receiver and from the air (interference from artificial
and natural sources, and ultimately the 2.7K background radiation from space).  Also resistive losses in any cable between receiver
and antenna will introduce noise too (more at higher RF frequencies).  Only the resistive elements of the losses will
be at 300 kelvin.  Interference may dominate if you are in a city, for instance.

Point a good antenna straight up and you'll often get a noise temperature well below 300K, but also interference from
satellites, the sun, Jupiter (again RF frequency dependent).

Given the antenna bandwidth is so wide it implies you are well into the UHF bands, I think this means less interference
in general, so thermal noise will dominate.

And you should use natural logs, not base 10 for that equation....   k T ln(bw)


My friend here is my experiment http://i1284.photobucket.com/albums/a578/fovos1/P6131098_zps37d09fcd.jpg

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