Mark wrote:
>>Reduce thermal noise by cooling the antenna. The noise is proportional
>>to kT, where k is Boltzmann's constant, and T is absolute temperature.
>>
> 
> 
> the physical temperature of the antenna itself contributes noise only
> due to the loss  in the antenna, usualy very small......you really need
> to cool what the antenna is "looking at", not the anteann itself...

That helps greatly, but if I could reach the source to cool it, I 
wouldn't need the antenna at all.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

> Reduce thermal noise by cooling the antenna. The noise is proportional
> to kT, where k is Boltzmann's constant, and T is absolute temperature.
>

the physical temperature of the antenna itself contributes noise only
due to the loss  in the antenna, usualy very small......you really need
to cool what the antenna is "looking at", not the anteann itself...


Mark

"thom" <soniceric@hotmail.com> wrote in message 
news:WcCdncPLDuMw0NPZnZ2dnUVZ_vWdnZ2d@giganews.com...
> Thanks for your answers. I'm going to explain what I would like to do a
> little more...
>
> I want to reduce the external noise, not internal noise generated by
> electronic.
Make your antenna very directional and point it at a quiet part of the sky.

>As you know, the RF input signal of a receiver contains noise.
> It is a small noise floor which can be considered as a white noise (its
> power is the same for all the frequencies).
>
> I just want to improve the C/N ratio, reducing noise in the band of the
> received signal. Maybe it is possible to reduce the noise inside the band,
> if you know how this noise is outside this band...
No - white means that you can't tell what is noise and what is signal by 
looking at noise in a different band. That is if you measure the noise in a 
band right next to the band that contains your signal plus noise , then 
subtract the noise measurement away you are actually adding more noise. If 
you could look at the noise in one band and determine what the noise 
component was in a seperate band then the noise in the two bands would be 
correlated - not white.

>Or maybe there are other
> methods to do it (as it is done for example in audio signals to reduce
> background noise...).
>
> Thanks
>
> Ps: the bandwidth of the signal could be larger than 1MHz

Best of Luck - Mike

thom wrote:
> Thanks for your answers. I'm going to explain what I would like to do a
> little more...
> 
> I want to reduce the external noise, not internal noise generated by
> electronic. As you know, the RF input signal of a receiver contains noise.
> It is a small noise floor which can be considered as a white noise (its
> power is the same for all the frequencies).
> 
> I just want to improve the C/N ratio, reducing noise in the band of the
> received signal. Maybe it is possible to reduce the noise inside the band,
> if you know how this noise is outside this band... Or maybe there are other
> methods to do it (as it is done for example in audio signals to reduce
> background noise...).
> 
> Thanks
> 
> Ps: the bandwidth of the signal could be larger than 1MHz

A bandpass filter with good skirt selectivity can reduce out-of-band 
noise. An antenna with good directional selectivity can reduce 
out-of-direction noise that is inside the band. As far as the receiver 
goes, whatever comes in on the antenna feed is part of the signal, 
whether or not you call it noise.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Jerry Avins skrev:
> thom wrote:
> > Hi everyone,
> >
> > I would like to reduce the noise in a receiver, just after the antenna
> > (where there is just a noise floor which is "white"). Do you know some
> > methods or a website concerning this noise reduction?
>
> Reduce thermal noise by cooling the antenna. The noise is proportional
> to kT, where k is Boltzmann's constant, and T is absolute temperature.
>
> Reduce atmospheric noise with a highly directional antenna, thus
> excluding from the system noise not in line with the desired signal.
>
> Reduce internal noise by using front-end components with lower noise
> figures (and cooling them).
>
> Resort to sorcery.

Nice list. You forgot one item, thoug, before or after your last:
Use your a priori knowledge of the signal you will obtain. If you have
enogh knowledge of that sort, you don't need the measurement.

Rune

Jerry Avins skrev:
> thom wrote:
> > Hi everyone,
> >
> > I would like to reduce the noise in a receiver, just after the antenna
> > (where there is just a noise floor which is "white"). Do you know some
> > methods or a website concerning this noise reduction?
>
> Reduce thermal noise by cooling the antenna. The noise is proportional
> to kT, where k is Boltzmann's constant, and T is absolute temperature.
>
> Reduce atmospheric noise with a highly directional antenna, thus
> excluding from the system noise not in line with the desired signal.
>
> Reduce internal noise by using front-end components with lower noise
> figures (and cooling them).
>
> Resort to sorcery.

Nice list. You forgot one item, thoug, before or after your last:
Use your a priori knowledge of the signal you will obtain. If you have
enogh knowledge of that sort, you don't need the measurement.

Rune

Thanks for your answers. I'm going to explain what I would like to do a
little more...

I want to reduce the external noise, not internal noise generated by
electronic. As you know, the RF input signal of a receiver contains noise.
It is a small noise floor which can be considered as a white noise (its
power is the same for all the frequencies).

I just want to improve the C/N ratio, reducing noise in the band of the
received signal. Maybe it is possible to reduce the noise inside the band,
if you know how this noise is outside this band... Or maybe there are other
methods to do it (as it is done for example in audio signals to reduce
background noise...).

Thanks

Ps: the bandwidth of the signal could be larger than 1MHz

thom wrote:
> Hi everyone,
> 
> I would like to reduce the noise in a receiver, just after the antenna
> (where there is just a noise floor which is "white"). Do you know some
> methods or a website concerning this noise reduction?

Reduce thermal noise by cooling the antenna. The noise is proportional 
to kT, where k is Boltzmann's constant, and T is absolute temperature.

Reduce atmospheric noise with a highly directional antenna, thus 
excluding from the system noise not in line with the desired signal.

Reduce internal noise by using front-end components with lower noise 
figures (and cooling them).

Resort to sorcery.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

thom wrote:
> Hi everyone,
> 
> I would like to reduce the noise in a receiver, just after the antenna
> (where there is just a noise floor which is "white"). Do you know some
> methods or a website concerning this noise reduction?
> 
> Thank you
> 
> Thom
> 
> 
You didn't tell us the band you're working in, whether your transmitter 
or receiver is mobile or portable, what the bandwidth of the signals 
are, whether they're digital or analog --  so I can't give you concrete 
guidance or suggestions.  None the less here's some general thoughts:

There are two possibilities:

1.  The noise is predominantly receiver noise.  This means that it can 
be reduced with a different receiver design featuring a lower-noise 
front-end.  You could possibly even reduce the noise with an outboard 
low noise amplifier, at the cost of some other receiver characteristics.

2.  The noise is coming from outside.  This would almost certainly be 
true if the frequency of interest is below 50MHz or so with an expensive 
receiver, with the frequency diminishing as the receiver front end gets 
cheaper.  Even in the GHz range its direct (expensive, but direct) to 
design receivers who's noise floor is lower than that of an antenna 
that's aimed at a room-temperature radiator.  If this is the case then 
the world's best low-noise receiver isn't going to do you any good.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

Hi everyone,

I would like to reduce the noise in a receiver, just after the antenna
(where there is just a noise floor which is "white"). Do you know some
methods or a website concerning this noise reduction?

Thank you

Thom