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How to Lower Noise Floor? - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


NewAlf
 Post subject: How to lower noise floor?
Posted: Tue May 30, 2006 10:50 pm 
 
Lieutenant

Joined: Sun May 28, 2006 6:29 pm
Posts: 3
Hello everyone,
I am working at the GigaHertz ragne with an antenna that produces a noise floor of -60dB. The expected signal has a peak of -58dB. Just wondering, how can i lower the noise floor to observe a clean signal?


 
   
 
karthik
 Post subject:
Posted: Wed May 31, 2006 12:00 am 
 
Colonel

Joined: Tue Apr 11, 2006 8:13 pm
Posts: 34
Hi,

Just wanted a clarification. What are you measuring? Are you measuring the signal at the output of the antenna or the output of a receiver? How are you measuring it? The -60 dBm level that you have indicated looks like the noise floor of the spetrum analyzer that you are using. If that is the case, then turn averaging on and also reduce the video bandwidth of the spec analyzer.

Karthik


 
   
 
NewAlf
 Post subject:
Posted: Wed May 31, 2006 2:07 am 
 
Lieutenant

Joined: Sun May 28, 2006 6:29 pm
Posts: 3
The antenna is being used to receive any singals from surroundings. The antenna is simply connected to the spec anal...I'll try turning averaging on and play with VBW...thnx for your reply..


 
   
 
nubbage
 Post subject:
Posted: Wed May 31, 2006 10:00 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
You could also buy an LNA covering the bandwidth of interest, then screen the antenna sidelobes from any hot sources such the earth, surrounding buildings etc.
The sensitivity/MDS level of -60dBm could be substantially improved on. The theoretical limit is calculated using the formula for noise power in a restistive load at temperature T in degrees Kelvin.

P = K*T*B*N Watts

Effectively N (the noise ratio of the LNA) adds to the temperature T when all parameters are converted to decibels, or just add the LNA noise temperature to the background temperature of the source (often the sky around a star). B is the system bandwidth in Hertz, and K is Boltzman's Constant.

Maybe the level you mention is because in your case B, the bandwidth, is very large.


 
   
 
asoft
 Post subject: spectrum analyzer measurements near noise floor.
Posted: Wed Jun 21, 2006 3:09 am 
 
Lieutenant

Joined: Sun Mar 05, 2006 10:38 am
Posts: 1
hi, what is the noise floor atainable with your spectrum analyzer? You can try reducing the frequency bandwidth, and increasing the RBW. If you know the exact frequency of the signals to be measured, it is suggested to reduce the frequecy and RBW sufficiently to get a clear signal. However, if -60db is the best you can get with lowest RBW and frequency span, it may be difficult to measure the signals. By the way, which spectrum analyzer are you using? (make and model)?


 
   
 
sivajo
 Post subject: Re: spectrum analyzer measurements near noise floor.
Posted: Mon Nov 06, 2006 10:54 pm 
 
Lieutenant

Joined: Mon Nov 06, 2006 10:40 pm
Posts: 2
Location: Shenzhen China
asoft wrote:
hi, what is the noise floor atainable with your spectrum analyzer? You can try reducing the frequency bandwidth, and increasing the RBW. If you know the exact frequency of the signals to be measured, it is suggested to reduce the frequecy and RBW sufficiently to get a clear signal. However, if -60db is the best you can get with lowest RBW and frequency span, it may be difficult to measure the signals. By the way, which spectrum analyzer are you using? (make and model)?


also try reducing ur spectum's attenation's pre-attenuation.




Posted  11/12/2012

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