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Antenna Amplifier Noise Figure

Started by rickman June 26, 2015
On 6/26/2015 9:46 PM, rickman wrote:
> On 6/26/2015 12:38 PM, amdx wrote: >> On 6/26/2015 7:24 AM, rickman wrote: >>> I read this post in an antenna group and I don't get how this guy is >>> coming up with a negative noise figure. Looks to me like he is >>> calculating the noise figure of a resistor, not the amplifier. Anyone >>> care to explain this to me? >>> >>> The part that seems bogus is this... >>> >>> > The negative NF is defined as the amplifier noise being less than the >>> > increase in noise due to the amplifier gain. >>> >>> I thought noise figure was NF = SNRin / SNRout >>> >>> Rick >>> >> I once ask Ratzlaff about the FSL antenna, in his comments he said, >> "high Q or low Q has little relation to how the FSL will actually >> perform for receiving weak signals.", but then went on to say, "Of >> course using Litz is the only type of wire to use." >> When I ask him about why Litz is important if Q isn't, he got pissed >> off and wrote back, "When you make sarcastic replies to the info I >> passed along, and question what I say, then I write you off as just a >> tire-kicker, not interested in possibly learning something, and I have >> no interest in saying anything more." >> Seems to me he said something incorrect and didn't like having someone >> ask him to clarify it. I'll leave it to you to figure out which part was >> incorrect. >> I thought Q would be important, an FSL is a ferrite loaded tuned loop. >> With magic mixed in! ;-) >> If Q is not important, why use Litz? >> I suspect you might have already tried to ask him, and now he's mad at >> you too! >> Mikek > > I suspect he said he didn't like your sarcastic replies because you made > sarcastic replies much more than he didn't want to discuss anything he > said. >
I was not being sarcastic in my response when I ask about the Litz. My understanding is Litz reduces R losses thus Q increases, if Q is not important, why is Litz the only type of wire to use? He probably realized that what he wrote made no sense and being ask about it offended his ego and I'm that's why got angry. On the other hand, if both of his statements are correct, it would be interesting to learn why. I would learn something, because as it stands, I can't reconcile the two statements. In the end, the ferrite loaded antenna I was working on had a low Q, I was using some surplus ferrite material I had, and it was lossy, especially in the upper AMBCB. It had Q's under 100 down to 40. To support Ratzlaff's theory, it did bring in stations that the radio didn't hear if not near the Ferrite loaded antenna. But that's subjective and I don't know what it would be like if it had a Q of 800. Mikek
On 6/27/2015 7:48 AM, amdx wrote:
> On 6/26/2015 9:46 PM, rickman wrote: >> On 6/26/2015 12:38 PM, amdx wrote: >>> On 6/26/2015 7:24 AM, rickman wrote: >>>> I read this post in an antenna group and I don't get how this guy is >>>> coming up with a negative noise figure. Looks to me like he is >>>> calculating the noise figure of a resistor, not the amplifier. Anyone >>>> care to explain this to me? >>>> >>>> The part that seems bogus is this... >>>> >>>> > The negative NF is defined as the amplifier noise being less than >>>> the >>>> > increase in noise due to the amplifier gain. >>>> >>>> I thought noise figure was NF = SNRin / SNRout >>>> >>>> Rick >>>> >>> I once ask Ratzlaff about the FSL antenna, in his comments he said, >>> "high Q or low Q has little relation to how the FSL will actually >>> perform for receiving weak signals.", but then went on to say, "Of >>> course using Litz is the only type of wire to use." >>> When I ask him about why Litz is important if Q isn't, he got pissed >>> off and wrote back, "When you make sarcastic replies to the info I >>> passed along, and question what I say, then I write you off as just a >>> tire-kicker, not interested in possibly learning something, and I have >>> no interest in saying anything more." >>> Seems to me he said something incorrect and didn't like having someone >>> ask him to clarify it. I'll leave it to you to figure out which part was >>> incorrect. >>> I thought Q would be important, an FSL is a ferrite loaded tuned >>> loop. >>> With magic mixed in! ;-) >>> If Q is not important, why use Litz? >>> I suspect you might have already tried to ask him, and now he's mad at >>> you too! >>> Mikek >> >> I suspect he said he didn't like your sarcastic replies because you made >> sarcastic replies much more than he didn't want to discuss anything he >> said. >> > I was not being sarcastic in my response when I ask about the Litz.
Look at the larger picture. -- Rick
On Sat, 27 Jun 2015 06:48:59 -0500, amdx <nojunk@knology.net> Gave us:

>On 6/26/2015 9:46 PM, rickman wrote: >> On 6/26/2015 12:38 PM, amdx wrote: >>> On 6/26/2015 7:24 AM, rickman wrote: >>>> I read this post in an antenna group and I don't get how this guy is >>>> coming up with a negative noise figure. Looks to me like he is >>>> calculating the noise figure of a resistor, not the amplifier. Anyone >>>> care to explain this to me? >>>> >>>> The part that seems bogus is this... >>>> >>>> > The negative NF is defined as the amplifier noise being less than the >>>> > increase in noise due to the amplifier gain. >>>> >>>> I thought noise figure was NF = SNRin / SNRout >>>> >>>> Rick >>>> >>> I once ask Ratzlaff about the FSL antenna, in his comments he said, >>> "high Q or low Q has little relation to how the FSL will actually >>> perform for receiving weak signals.", but then went on to say, "Of >>> course using Litz is the only type of wire to use." >>> When I ask him about why Litz is important if Q isn't, he got pissed >>> off and wrote back, "When you make sarcastic replies to the info I >>> passed along, and question what I say, then I write you off as just a >>> tire-kicker, not interested in possibly learning something, and I have >>> no interest in saying anything more." >>> Seems to me he said something incorrect and didn't like having someone >>> ask him to clarify it. I'll leave it to you to figure out which part was >>> incorrect. >>> I thought Q would be important, an FSL is a ferrite loaded tuned loop. >>> With magic mixed in! ;-) >>> If Q is not important, why use Litz? >>> I suspect you might have already tried to ask him, and now he's mad at >>> you too! >>> Mikek >> >> I suspect he said he didn't like your sarcastic replies because you made >> sarcastic replies much more than he didn't want to discuss anything he >> said. >> > I was not being sarcastic in my response when I ask about the Litz. >My understanding is Litz reduces R losses thus Q increases, if Q is not >important, why is Litz the only type of wire to use? >He probably realized that what he wrote made no sense and being ask >about it offended his ego and I'm that's why got angry. > On the other hand, if both of his statements are correct, it would be >interesting to learn why. I would learn something, because as it stands, >I can't reconcile the two statements. > In the end, the ferrite loaded antenna I was working on had a low Q, >I was using some surplus ferrite material I had, and it was lossy, >especially in the upper AMBCB. It had Q's under 100 down to 40. To >support Ratzlaff's theory, it did bring in stations that the radio >didn't hear if not near the Ferrite loaded antenna. But that's >subjective and I don't know what it would be like if it had a Q of 800. > Mikek
The &#2013266101; of the ferrite makes a difference. Especially in cost.. There is also an "ideal" (or nearly so) diameter (and length) to best use. One can buy one inch specimens and glue them together when tuning to find a "best use" scenario for the desired fo under which to continue tuning practices.
On 6/27/2015 4:07 AM, Jeff wrote:
> On 26/06/2015 13:24, rickman wrote: >> I read this post in an antenna group and I don't get how this guy is >> coming up with a negative noise figure. Looks to me like he is >> calculating the noise figure of a resistor, not the amplifier. Anyone >> care to explain this to me? >> >> The part that seems bogus is this... >> >> > The negative NF is defined as the amplifier noise being less than the >> > increase in noise due to the amplifier gain. >> >> I thought noise figure was NF = SNRin / SNRout >> >> Rick >> > > Both definitions are correct and mean the same thing; a negative NF, > when expressed in dB, would be when the SNRout is less than the SNRin. > However, the big but is that an negative NF is not possible.
I don't think both definitions mean the same thing. If the amplifier adds *any* noise it increases the NF above zero by the conventional definition. The only way the NF can be negative is if the amplifier removes noise from the input, or in other words, increases the SNR. What he seems to be suggesting is that NF is the ratio of the signal noise to the amplifier noise.
> It only appears to be the case due to the fact that the OP is not > comparing like with like, the test method used is only valid if the > system impedance remains the same. You cannot compare oranges with lemons.
-- Rick
On 27/06/2015 13:26, rickman wrote:
> On 6/27/2015 4:07 AM, Jeff wrote: >> On 26/06/2015 13:24, rickman wrote: >>> I read this post in an antenna group and I don't get how this guy is >>> coming up with a negative noise figure. Looks to me like he is >>> calculating the noise figure of a resistor, not the amplifier. Anyone >>> care to explain this to me? >>> >>> The part that seems bogus is this... >>> >>> > The negative NF is defined as the amplifier noise being less than the >>> > increase in noise due to the amplifier gain. >>> >>> I thought noise figure was NF = SNRin / SNRout >>> >>> Rick >>> >> >> Both definitions are correct and mean the same thing; a negative NF, >> when expressed in dB, would be when the SNRout is less than the SNRin. >> However, the big but is that an negative NF is not possible. > > I don't think both definitions mean the same thing. If the amplifier > adds *any* noise it increases the NF above zero by the conventional > definition. The only way the NF can be negative is if the amplifier > removes noise from the input, or in other words, increases the SNR. >
Yes that is correct, but the definitions are also correct. The flaw in the negative noise figure argument is that it is not possible to have a better SNRout than SNRin *for the same system conditions*. The apparent negative noise figure only come about by comparing the NF of the amp in a 50ohm system with the output from a system with something different on the input. The test method used is also very prone to measurement errors for low noise figures. Jeff
> Is that formula correct? If the input SNR is poor, an amplifier with a > high NF has very impact on the output SNR. > > Also, are the units ratios, or are they in dB? >> >
For a particular NF the effect on the output s/n ratio is always the same regardless of the actual input s/n, until you get to the point where the signal vanishes in the noise, but even then it still holds true but you just can't see it. The signal will go up by the gain of the amplifier, and the noise will go up by the sum of *power* of the input noise times the gain and the noise power of the calculated from the NF times the gain. The noise powers being in watts calculated from the NF; in a 1Hz Bandwidth by convention. So its dB above kTB converted to watts if you are working with NF in dB. So for a particular NF the added noise is always the same, therefore the SNRin/SNRout holds, and is a standard definition of NF (not in dB). Jeff
On Sat, 27 Jun 2015 13:43:16 +0100, Jeff <jeff@ukra.com> Gave us:

>On 27/06/2015 13:26, rickman wrote: >> On 6/27/2015 4:07 AM, Jeff wrote: >>> On 26/06/2015 13:24, rickman wrote: >>>> I read this post in an antenna group and I don't get how this guy is >>>> coming up with a negative noise figure. Looks to me like he is >>>> calculating the noise figure of a resistor, not the amplifier. Anyone >>>> care to explain this to me? >>>> >>>> The part that seems bogus is this... >>>> >>>> > The negative NF is defined as the amplifier noise being less than the >>>> > increase in noise due to the amplifier gain. >>>> >>>> I thought noise figure was NF = SNRin / SNRout >>>> >>>> Rick >>>> >>> >>> Both definitions are correct and mean the same thing; a negative NF, >>> when expressed in dB, would be when the SNRout is less than the SNRin. >>> However, the big but is that an negative NF is not possible. >> >> I don't think both definitions mean the same thing. If the amplifier >> adds *any* noise it increases the NF above zero by the conventional >> definition. The only way the NF can be negative is if the amplifier >> removes noise from the input, or in other words, increases the SNR. >> > >Yes that is correct, but the definitions are also correct. The flaw in >the negative noise figure argument is that it is not possible to have a >better SNRout than SNRin *for the same system conditions*. > >The apparent negative noise figure only come about by comparing the NF >of the amp in a 50ohm system with the output from a system with >something different on the input. > >The test method used is also very prone to measurement errors for low >noise figures. > >Jeff
To me, NF refers to "noise floor". Lets see him go below that. GPS received signals are among the lowest "power" signals we currently grab. They sit just above the noise floor.
On Sat, 27 Jun 2015 14:02:49 +0100, Jeff <jeff@ukra.com> Gave us:

> >> Is that formula correct? If the input SNR is poor, an amplifier with a >> high NF has very impact on the output SNR. >> >> Also, are the units ratios, or are they in dB? >>> >> > >For a particular NF the effect on the output s/n ratio is always the >same regardless of the actual input s/n, until you get to the point >where the signal vanishes in the noise, but even then it still holds >true but you just can't see it. > >The signal will go up by the gain of the amplifier, and the noise will >go up by the sum of *power* of the input noise times the gain and the >noise power of the calculated from the NF times the gain. > >The noise powers being in watts calculated from the NF; in a 1Hz >Bandwidth by convention. So its dB above kTB converted to watts if you >are working with NF in dB. > >So for a particular NF the added noise is always the same, therefore the >SNRin/SNRout holds, and is a standard definition of NF (not in dB). > >Jeff
https://en.wikipedia.org/wiki/DBm Look at the last four entries in the table.
On 6/27/2015 7:11 AM, DecadentLinuxUserNumeroUno wrote:
> On Sat, 27 Jun 2015 06:48:59 -0500, amdx <nojunk@knology.net> Gave us: > >> On 6/26/2015 9:46 PM, rickman wrote: >>> On 6/26/2015 12:38 PM, amdx wrote: >>>> On 6/26/2015 7:24 AM, rickman wrote: >>>>> I read this post in an antenna group and I don't get how this guy is >>>>> coming up with a negative noise figure. Looks to me like he is >>>>> calculating the noise figure of a resistor, not the amplifier. Anyone >>>>> care to explain this to me? >>>>> >>>>> The part that seems bogus is this... >>>>> >>>>> > The negative NF is defined as the amplifier noise being less than the >>>>> > increase in noise due to the amplifier gain. >>>>> >>>>> I thought noise figure was NF = SNRin / SNRout >>>>> >>>>> Rick >>>>> >>>> I once ask Ratzlaff about the FSL antenna, in his comments he said, >>>> "high Q or low Q has little relation to how the FSL will actually >>>> perform for receiving weak signals.", but then went on to say, "Of >>>> course using Litz is the only type of wire to use." >>>> When I ask him about why Litz is important if Q isn't, he got pissed >>>> off and wrote back, "When you make sarcastic replies to the info I >>>> passed along, and question what I say, then I write you off as just a >>>> tire-kicker, not interested in possibly learning something, and I have >>>> no interest in saying anything more." >>>> Seems to me he said something incorrect and didn't like having someone >>>> ask him to clarify it. I'll leave it to you to figure out which part was >>>> incorrect. >>>> I thought Q would be important, an FSL is a ferrite loaded tuned loop. >>>> With magic mixed in! ;-) >>>> If Q is not important, why use Litz? >>>> I suspect you might have already tried to ask him, and now he's mad at >>>> you too! >>>> Mikek >>> >>> I suspect he said he didn't like your sarcastic replies because you made >>> sarcastic replies much more than he didn't want to discuss anything he >>> said. >>> >> I was not being sarcastic in my response when I ask about the Litz. >> My understanding is Litz reduces R losses thus Q increases, if Q is not >> important, why is Litz the only type of wire to use? >> He probably realized that what he wrote made no sense and being ask >> about it offended his ego and I'm that's why got angry. >> On the other hand, if both of his statements are correct, it would be >> interesting to learn why. I would learn something, because as it stands, >> I can't reconcile the two statements. >> In the end, the ferrite loaded antenna I was working on had a low Q, >> I was using some surplus ferrite material I had, and it was lossy, >> especially in the upper AMBCB. It had Q's under 100 down to 40. To >> support Ratzlaff's theory, it did bring in stations that the radio >> didn't hear if not near the Ferrite loaded antenna. But that's >> subjective and I don't know what it would be like if it had a Q of 800. >> Mikek > > The &#2013266101; of the ferrite makes a difference. > > Especially in cost.. > > There is also an "ideal" (or nearly so) diameter (and length) to best > use. > > One can buy one inch specimens and glue them together when tuning to > find a "best use" scenario for the desired fo under which to continue > tuning practices. >
These FSL antennas are a different breed, they use 10's of rods or bars in a 4" to 10"+ diameter cylinder. Then a coil is wrapped around and tuned with an air capacitor. Here's a good link. http://www.am-dx.com/antennas/FSL%20Antenna%20Design%20Optimization.htm Mikek --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com
> To me, NF refers to "noise floor". > > Lets see him go below that. > > GPS received signals are among the lowest "power" signals we currently > grab. They sit just above the noise floor. >
It might to you, but in this context it means either Noise Factor or Noise Figure. Of course you can go below the Noise Floor, and in some circumstances and modes the signal is receivable and decodable. Jeff