Topics

Newbie question.


Luc , on4aol
 

Goodmorning to all,
After experiments with Q100 , i' want to  take a new step in the microwave region.
First step is receiving the ON0EME   EME beacon . I made calculations ( with VK3UM EMEcalc and others ) if i have enough SNR to take this step .
Well , it 's difficult ! Only with a bandwidth of 10 Hz there is about 3 dB SNR , not very much.
But , my really concern is the next issue. Think in the next moment we have NO noise ( theoretical assumption).
If a have a LNA that can amplify a minimum signal that is on a level of , let's say -160dBm.
Suppose the Gain is 20 dB , then the output delivers =  - 140dBm.
Is this really so ? Or is there a ( physical) threshold before the LNA " kicks in" .
Can we project this to all the levels  i.e.  -180 dBm gives - 160 dBm ? ( remember , there is  no noise) .

I welcome any comment.

73  Luc  ON4AOL


Robin Szemeti - G1YFG
 

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 ..


On Mon, 4 Jan 2021 at 10:22, Luc , on4aol <luc.van.achte@...> wrote:
Goodmorning to all,
After experiments with Q100 , i' want to  take a new step in the microwave region.
First step is receiving the ON0EME   EME beacon . I made calculations ( with VK3UM EMEcalc and others ) if i have enough SNR to take this step .
Well , it 's difficult ! Only with a bandwidth of 10 Hz there is about 3 dB SNR , not very much.
But , my really concern is the next issue. Think in the next moment we have NO noise ( theoretical assumption).
If a have a LNA that can amplify a minimum signal that is on a level of , let's say -160dBm.
Suppose the Gain is 20 dB , then the output delivers =  - 140dBm.
Is this really so ? Or is there a ( physical) threshold before the LNA " kicks in" .
Can we project this to all the levels  i.e.  -180 dBm gives - 160 dBm ? ( remember , there is  no noise) .

I welcome any comment.

73  Luc  ON4AOL


--
Robin Szemeti - G1YFG


Luc , on4aol
 

Hi Robin ,
Tnx for the quick reply.
Now i know that i am on the right track what my idea about amplification concerned.
And yes i know , there is no real world without noise.
Have a  nice day !
73 Luc ON4AOL


Brian Howie GM4DIJ
 

In message <hijh.1609755777674220352.sAJb@groups.io>, "Luc , on4aol" <luc.van.achte@telenet.be> writes
Goodmorning to all,
After experiments with Q100 , i' want to  take a new step in the
microwave region.
First step is receiving the ON0EME   EME beacon . I made calculations (
with VK3UM EMEcalc and others ) if i have enough SNR to take this step
.
Well , it 's difficult ! Only with a bandwidth of 10 Hz there is about
3 dB SNR , not very much.
But , my really concern is the next issue. Think in the next moment we
have NO noise ( theoretical assumption).
If a have a LNA that can amplify a minimum signal that is on a level of
, let's say -160dBm.
Suppose the Gain is 20 dB , then the output delivers =  - 140dBm.
Is this really so ? Or is there a ( physical) threshold before the LNA
" kicks in" .
Can we project this to all the levels  i.e.  -180 dBm gives - 160 dBm ?
( remember , there is  no noise) .
I welcome any comment.
73  Luc  ON4AOL
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


John E. Beech
 

I've always assumed that increasing antenna gain ie bigger dish increases the wanted signal without increasing the noise
received ie improves the s/n ratio but thinking about it I'm not so sure this is true. Increasing antenna gain means
reducing beamwidth which in turn means the antenna is looking at more moon and less sky, so more wanted signal but
also more noise from the moon, which will be hotter than (deep) space*. Also increasing the dish size increases the area
of a comparatively hot surface (terrestrial antenna) radiating/focusing noise towards the feed point. So what's best? Big
antenna or high gain LNA with lowest possible noise figure?

* Local space may have a higher noise figure depending on where the sun & moon are in the sky.

de John G8SEQ

-------Original Message-------
From: Robin Szemeti - G1YFG <robin@redpoint.org.uk>
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] Newbie question.
Sent: Jan 04 '21 12:25

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 ..

On Mon, 4 Jan 2021 at 10:22, Luc , on4aol <luc.van.achte@telenet.be>
wrote:

> Goodmorning to all,
> After experiments with Q100 , i' want to take a new step in the
> microwave region.
> First step is receiving the ON0EME EME beacon . I made calculations
> ( with VK3UM EMEcalc and others ) if i have enough SNR to take this
> step .
> Well , it 's difficult ! Only with a bandwidth of 10 Hz there is
> about 3 dB SNR , not very much.
> But , my really concern is the next issue. Think in the next moment
> we have NO noise ( theoretical assumption).
> If a have a LNA that can amplify a minimum signal that is on a
> level of , let's say -160dBm.
> Suppose the Gain is 20 dB , then the output delivers = - 140dBm.
> Is this really so ? Or is there a ( physical) threshold before the
> LNA " kicks in" .
> Can we project this to all the levels i.e. -180 dBm gives - 160 dBm
> ? ( remember , there is no noise) .
>
> I welcome any comment.
>
> 73 Luc ON4AOL

--
Robin Szemeti - G1YFG


Brian Howie GM4DIJ
 

In message <20210104200247.20483.qmail@s468.sureserver.com>, John E. Beech <john@g8seq.com> writes

You hit a limit where the antenna beamwidth is smaller than the angular subtense of the Moon. The signal stops increasing. The VK3UM program warns you when this happens, as it did to me today looking into the 10 GHZ EME beacon.


Brian GM4DIJ

I've always assumed that increasing antenna gain ie bigger dish increases the wanted signal without increasing the noise
received ie improves the s/n ratio but thinking about it I'm not so sure this is true. Increasing antenna gain means
reducing beamwidth which in turn means the antenna is looking at more moon and less sky, so more wanted signal but
also more noise from the moon, which will be hotter than (deep) space*. Also increasing the dish size increases the area
of a comparatively hot surface (terrestrial antenna) radiating/focusing noise towards the feed point. So what's best? Big
antenna or high gain LNA with lowest possible noise figure?

* Local space may have a higher noise figure depending on where the sun & moon are in the sky.

de John G8SEQ

-------Original Message-------
From: Robin Szemeti - G1YFG <robin@redpoint.org.uk>
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] Newbie question.
Sent: Jan 04 '21 12:25

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 ..

On Mon, 4 Jan 2021 at 10:22, Luc , on4aol <luc.van.achte@telenet.be>
wrote:

> Goodmorning to all,
> After experiments with Q100 , i' want to take a new step in the
> microwave region.
> First step is receiving the ON0EME EME beacon . I made calculations
> ( with VK3UM EMEcalc and others ) if i have enough SNR to take this
> step .
> Well , it 's difficult ! Only with a bandwidth of 10 Hz there is
> about 3 dB SNR , not very much.
> But , my really concern is the next issue. Think in the next moment
> we have NO noise ( theoretical assumption).
> If a have a LNA that can amplify a minimum signal that is on a
> level of , let's say -160dBm.
> Suppose the Gain is 20 dB , then the output delivers = - 140dBm.
> Is this really so ? Or is there a ( physical) threshold before the
> LNA " kicks in" .
> Can we project this to all the levels i.e. -180 dBm gives - 160 dBm
> ? ( remember , there is no noise) .
>
> I welcome any comment.
>
> 73 Luc ON4AOL

--
Robin Szemeti - G1YFG



--
Brian Howie


Luc , on4aol
 

Ok , tnx Brian ,

If a have  to upgrade my system,  it's better to try at first hand to improve my Tsystem and then think about a LNA with a better  SNR
Thanks for all comments

73  Luc ON4AOL
https://on4aol.blogspot.com/