JH
Javier Herrero
Sat, Oct 22, 2011 12:50 PM
Hello all,
Perhaps a bit OT, but I'm measuring the output noise density of a noise
source at a puntual frequency. I've fed the noise output to a 8566B
spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so the
displayed trace is flat. I obtain a measurement of -45dBm, and I
understand that the noise density then is -105dBm/Hz.
From design variables, I was expecting a somewhat lower value, around
-110dBm/Hz, but between the NoiseCom noise source and the output there
are several things (attenuator, filter, amplifier, directional coupler,
variable attenuator, ...), so perhaps there are slight differences
between estimated insertion gains and losses accumulate up to 5dB.
Before dismount the system and look directly at the noise source output
and measure the losses/gains of each element, I would like to know if I
am doing this mesasurement right or am I commiting some mistake?
Thanks! Best regards,
Javier, EA1CRB
Hello all,
Perhaps a bit OT, but I'm measuring the output noise density of a noise
source at a puntual frequency. I've fed the noise output to a 8566B
spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so the
displayed trace is flat. I obtain a measurement of -45dBm, and I
understand that the noise density then is -105dBm/Hz.
From design variables, I was expecting a somewhat lower value, around
-110dBm/Hz, but between the NoiseCom noise source and the output there
are several things (attenuator, filter, amplifier, directional coupler,
variable attenuator, ...), so perhaps there are slight differences
between estimated insertion gains and losses accumulate up to 5dB.
Before dismount the system and look directly at the noise source output
and measure the losses/gains of each element, I would like to know if I
am doing this mesasurement right or am I commiting some mistake?
Thanks! Best regards,
Javier, EA1CRB
JL
Jim Lux
Sat, Oct 22, 2011 1:13 PM
On 10/22/11 5:50 AM, Javier Herrero wrote:
Hello all,
Perhaps a bit OT, but I'm measuring the output noise density of a noise
source at a puntual frequency. I've fed the noise output to a 8566B
spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so the
displayed trace is flat. I obtain a measurement of -45dBm, and I
understand that the noise density then is -105dBm/Hz.
From design variables, I was expecting a somewhat lower value, around
-110dBm/Hz, but between the NoiseCom noise source and the output there
are several things (attenuator, filter, amplifier, directional coupler,
variable attenuator, ...), so perhaps there are slight differences
between estimated insertion gains and losses accumulate up to 5dB.
Before dismount the system and look directly at the noise source output
and measure the losses/gains of each element, I would like to know if I
am doing this mesasurement right or am I commiting some mistake?
Two things spring to mind:
Spectrum analyzers don't have very low noise inputs, in general. Did
you account for the additional noise from that source?
The noise bandwidth is not necessarily the same as the resolution
bandwidth (the shape of the filter isn't rectangular, after all). You'd
have to look at the phase noise measuring ap notes from HP, I think they
give the correction factor to use (it's more than a dB, as I recall)
On 10/22/11 5:50 AM, Javier Herrero wrote:
> Hello all,
>
> Perhaps a bit OT, but I'm measuring the output noise density of a noise
> source at a puntual frequency. I've fed the noise output to a 8566B
> spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so the
> displayed trace is flat. I obtain a measurement of -45dBm, and I
> understand that the noise density then is -105dBm/Hz.
>
> From design variables, I was expecting a somewhat lower value, around
> -110dBm/Hz, but between the NoiseCom noise source and the output there
> are several things (attenuator, filter, amplifier, directional coupler,
> variable attenuator, ...), so perhaps there are slight differences
> between estimated insertion gains and losses accumulate up to 5dB.
> Before dismount the system and look directly at the noise source output
> and measure the losses/gains of each element, I would like to know if I
> am doing this mesasurement right or am I commiting some mistake?
Two things spring to mind:
Spectrum analyzers don't have very low noise inputs, in general. Did
you account for the additional noise from that source?
The noise bandwidth is not necessarily the same as the resolution
bandwidth (the shape of the filter isn't rectangular, after all). You'd
have to look at the phase noise measuring ap notes from HP, I think they
give the correction factor to use (it's more than a dB, as I recall)
SR
Sylvain RICHARD
Sat, Oct 22, 2011 1:57 PM
Le 22/10/2011 14:50, Javier Herrero a écrit :
Hello all,
Perhaps a bit OT, but I'm measuring the output noise density of a
noise source at a puntual frequency. I've fed the noise output to a
8566B spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so
the displayed trace is flat. I obtain a measurement of -45dBm, and I
understand that the noise density then is -105dBm/Hz.
From design variables, I was expecting a somewhat lower value, around
-110dBm/Hz, but between the NoiseCom noise source and the output there
are several things (attenuator, filter, amplifier, directional
coupler, variable attenuator, ...), so perhaps there are slight
differences between estimated insertion gains and losses accumulate up
to 5dB. Before dismount the system and look directly at the noise
source output and measure the losses/gains of each element, I would
like to know if I am doing this mesasurement right or am I commiting
some mistake?
Thanks! Best regards,
Javier, EA1CRB
Javier,
Short answer:
- make sure that the noise level increases at least 10 dB when you
connect the noise source.
- check that there is no hidden compression by manually controlling the
input attenuator and (not sure if this works on a 8566B) the IF amps /
reference level. Levels should remain constant. Don't fry your input
mixer: -10 dBm max for specified linearity. Total power in your case =
-105 dBm/Hz in many gigahertz plus (unknown) amplification.
- use the noise marker (shift+M) to take care of the well-known ~2 dB
difference between proper power detection and what the analyzer does.
Long answer:
Agilent appnote 1303, aka 5966-4008E "Spectrum and Signal Analyzer
Measurements and Noise"
http://cp.literature.agilent.com/litweb/pdf/5966-4008E.pdf
Have fun!
--
Sylvain RICHARD
Le 22/10/2011 14:50, Javier Herrero a écrit :
> Hello all,
>
> Perhaps a bit OT, but I'm measuring the output noise density of a
> noise source at a puntual frequency. I've fed the noise output to a
> 8566B spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so
> the displayed trace is flat. I obtain a measurement of -45dBm, and I
> understand that the noise density then is -105dBm/Hz.
>
> From design variables, I was expecting a somewhat lower value, around
> -110dBm/Hz, but between the NoiseCom noise source and the output there
> are several things (attenuator, filter, amplifier, directional
> coupler, variable attenuator, ...), so perhaps there are slight
> differences between estimated insertion gains and losses accumulate up
> to 5dB. Before dismount the system and look directly at the noise
> source output and measure the losses/gains of each element, I would
> like to know if I am doing this mesasurement right or am I commiting
> some mistake?
>
> Thanks! Best regards,
>
> Javier, EA1CRB
Javier,
Short answer:
1) make sure that the noise level increases at least 10 dB when you
connect the noise source.
2) check that there is no hidden compression by manually controlling the
input attenuator and (not sure if this works on a 8566B) the IF amps /
reference level. Levels should remain constant. Don't fry your input
mixer: -10 dBm max for specified linearity. Total power in your case =
-105 dBm/Hz in many gigahertz plus (unknown) amplification.
3) use the noise marker (shift+M) to take care of the well-known ~2 dB
difference between proper power detection and what the analyzer does.
Long answer:
Agilent appnote 1303, aka 5966-4008E "Spectrum and Signal Analyzer
Measurements and Noise"
http://cp.literature.agilent.com/litweb/pdf/5966-4008E.pdf
Have fun!
--
Sylvain RICHARD
G/
Graham / KE9H
Sat, Oct 22, 2011 2:49 PM
On 10/22/2011 7:50 AM, Javier Herrero wrote:
Hello all,
Perhaps a bit OT, but I'm measuring the output noise density of a
noise source at a puntual frequency. I've fed the noise output to a
8566B spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so
the displayed trace is flat. I obtain a measurement of -45dBm, and I
understand that the noise density then is -105dBm/Hz.
From design variables, I was expecting a somewhat lower value, around
-110dBm/Hz, but between the NoiseCom noise source and the output there
are several things (attenuator, filter, amplifier, directional
coupler, variable attenuator, ...), so perhaps there are slight
differences between estimated insertion gains and losses accumulate up
to 5dB. Before dismount the system and look directly at the noise
source output and measure the losses/gains of each element, I would
like to know if I am doing this mesasurement right or am I commiting
some mistake?
Thanks! Best regards,
Javier, EA1CRB
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Javier:
When you say your Spectrum Analyzer bandwidth is set to 1 MHz, do you
mean the frequency span width of the screen?
I would think that your receiver bandwidth is the Video Bandwidth,
therefore 1 kHz.
Correction for noise bandwidth is an adjustment for power, proportional to
bandwidth, therefore 10log(BW1/BW2)
Correcting 1 KHz to 1 Hz is therefore a 30 dB adjustment, not a 60 dB
adjustment.
I think what you are measuring is more like -75dBm/Hz.
--- Graham / KE9H
==
On 10/22/2011 7:50 AM, Javier Herrero wrote:
> Hello all,
>
> Perhaps a bit OT, but I'm measuring the output noise density of a
> noise source at a puntual frequency. I've fed the noise output to a
> 8566B spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so
> the displayed trace is flat. I obtain a measurement of -45dBm, and I
> understand that the noise density then is -105dBm/Hz.
>
> From design variables, I was expecting a somewhat lower value, around
> -110dBm/Hz, but between the NoiseCom noise source and the output there
> are several things (attenuator, filter, amplifier, directional
> coupler, variable attenuator, ...), so perhaps there are slight
> differences between estimated insertion gains and losses accumulate up
> to 5dB. Before dismount the system and look directly at the noise
> source output and measure the losses/gains of each element, I would
> like to know if I am doing this mesasurement right or am I commiting
> some mistake?
>
> Thanks! Best regards,
>
> Javier, EA1CRB
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
Javier:
When you say your Spectrum Analyzer bandwidth is set to 1 MHz, do you
mean the frequency span width of the screen?
I would think that your receiver bandwidth is the Video Bandwidth,
therefore 1 kHz.
Correction for noise bandwidth is an adjustment for power, proportional to
bandwidth, therefore 10log(BW1/BW2)
Correcting 1 KHz to 1 Hz is therefore a 30 dB adjustment, not a 60 dB
adjustment.
I think what you are measuring is more like -75dBm/Hz.
--- Graham / KE9H
==
MF
Mike Feher
Sat, Oct 22, 2011 3:06 PM
Javier -
I believe you are indeed close. With the IF BW at 1 MHz the correction is
indeed 60 dB. The post detection filtering by the video filter only makes it
look nicer but does not come into play. I believe there are two correction
factors that you need to take into consideration, that, as I recall, comes
close to about 2.5 dB total. I may be off on that number, but, it is close
to that (I am sure you can Google it). You will read more because the filter
BW is off course not perfect, and the equivalent noise BW is greater than 1
MHz. I believe there is a correction for that. The other, is how the
detector inside the analyzer treats noise instead of a pure sine wave. Those
corrections will get you closer to your expected value, and, maybe the
others are due to your losses. 73 - Mike
Mike B. Feher, EOZ Inc.
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 (B)
908-902-3831 (C)
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Javier Herrero
Sent: Saturday, October 22, 2011 8:51 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Noise source measurement
Hello all,
Perhaps a bit OT, but I'm measuring the output noise density of a noise
source at a puntual frequency. I've fed the noise output to a 8566B
spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so the
displayed trace is flat. I obtain a measurement of -45dBm, and I
understand that the noise density then is -105dBm/Hz.
From design variables, I was expecting a somewhat lower value, around
-110dBm/Hz, but between the NoiseCom noise source and the output there
are several things (attenuator, filter, amplifier, directional coupler,
variable attenuator, ...), so perhaps there are slight differences
between estimated insertion gains and losses accumulate up to 5dB.
Before dismount the system and look directly at the noise source output
and measure the losses/gains of each element, I would like to know if I
am doing this mesasurement right or am I commiting some mistake?
Thanks! Best regards,
Javier, EA1CRB
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Javier -
I believe you are indeed close. With the IF BW at 1 MHz the correction is
indeed 60 dB. The post detection filtering by the video filter only makes it
look nicer but does not come into play. I believe there are two correction
factors that you need to take into consideration, that, as I recall, comes
close to about 2.5 dB total. I may be off on that number, but, it is close
to that (I am sure you can Google it). You will read more because the filter
BW is off course not perfect, and the equivalent noise BW is greater than 1
MHz. I believe there is a correction for that. The other, is how the
detector inside the analyzer treats noise instead of a pure sine wave. Those
corrections will get you closer to your expected value, and, maybe the
others are due to your losses. 73 - Mike
Mike B. Feher, EOZ Inc.
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 (B)
908-902-3831 (C)
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Javier Herrero
Sent: Saturday, October 22, 2011 8:51 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Noise source measurement
Hello all,
Perhaps a bit OT, but I'm measuring the output noise density of a noise
source at a puntual frequency. I've fed the noise output to a 8566B
spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so the
displayed trace is flat. I obtain a measurement of -45dBm, and I
understand that the noise density then is -105dBm/Hz.
From design variables, I was expecting a somewhat lower value, around
-110dBm/Hz, but between the NoiseCom noise source and the output there
are several things (attenuator, filter, amplifier, directional coupler,
variable attenuator, ...), so perhaps there are slight differences
between estimated insertion gains and losses accumulate up to 5dB.
Before dismount the system and look directly at the noise source output
and measure the losses/gains of each element, I would like to know if I
am doing this mesasurement right or am I commiting some mistake?
Thanks! Best regards,
Javier, EA1CRB
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
JH
Javier Herrero
Sat, Oct 22, 2011 7:17 PM
El 22/10/2011 15:13, Jim Lux escribió:
Two things spring to mind:
Spectrum analyzers don't have very low noise inputs, in general. Did
you account for the additional noise from that source?
The noise bandwidth is not necessarily the same as the resolution
bandwidth (the shape of the filter isn't rectangular, after all).
You'd have to look at the phase noise measuring ap notes from HP, I
think they give the correction factor to use (it's more than a dB, as
I recall)
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Thanks, Jim. Yes, I've accounted it, the noise source is around 20dB
over the analyzer noise, so analyzer noise can be neglected. I was
missing the correction due to the filter form factor, and thanks,
Sylvain, for pointing me to the application note, that shows this
correction and other more important (in dB terms) due to the log
detection and averaging process of the video filter, so I must add
2.51dB, and substract 0.51dB due to the filter shape, so I must correct
add 2dB. I see that the shift-M function already provides this
correction (I was missing that! Thanks!)
I've make sure that no analyzer compression or overloading is taking
place. Also, the bandwidth of the noise source is limited to approx.
1.2GHz, centered at 8.2GHz, so the analyzer does not see too much noise
power (around -15dBm total noise power). I've checked changing the
attenuation values from 0, 10 and 20dB and the analyzer noise floor
varies as expected, but the noise source measurement does not change.
I was missing also to add a 1.2dB for the analyzer cable loss, and after
playing a bit around, the value I get at the center frequency is
-102dBm/Hz, around 8dB higher that I was expecting, but probably the
measurement is ok and the fixed losses due to the other elements were
somewhat overestimated during the design, and the gain of the amplifier
that is in the noise path is a bit higher than expected. I will measure
directly at the noise source output, and check losses and amplifier
gain, but to have a bit more of noise available is not a problem in this
case (in fact, it is an advantage). Mainly I was looking to be sure that
I was measuring it in the right way, so thank you very much for your help.
Best regards,
Javier, EA1CRB
El 22/10/2011 15:13, Jim Lux escribió:
>
> Two things spring to mind:
>
> Spectrum analyzers don't have very low noise inputs, in general. Did
> you account for the additional noise from that source?
>
> The noise bandwidth is not necessarily the same as the resolution
> bandwidth (the shape of the filter isn't rectangular, after all).
> You'd have to look at the phase noise measuring ap notes from HP, I
> think they give the correction factor to use (it's more than a dB, as
> I recall)
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>
Thanks, Jim. Yes, I've accounted it, the noise source is around 20dB
over the analyzer noise, so analyzer noise can be neglected. I was
missing the correction due to the filter form factor, and thanks,
Sylvain, for pointing me to the application note, that shows this
correction and other more important (in dB terms) due to the log
detection and averaging process of the video filter, so I must add
2.51dB, and substract 0.51dB due to the filter shape, so I must correct
add 2dB. I see that the shift-M function already provides this
correction (I was missing that! Thanks!)
I've make sure that no analyzer compression or overloading is taking
place. Also, the bandwidth of the noise source is limited to approx.
1.2GHz, centered at 8.2GHz, so the analyzer does not see too much noise
power (around -15dBm total noise power). I've checked changing the
attenuation values from 0, 10 and 20dB and the analyzer noise floor
varies as expected, but the noise source measurement does not change.
I was missing also to add a 1.2dB for the analyzer cable loss, and after
playing a bit around, the value I get at the center frequency is
-102dBm/Hz, around 8dB higher that I was expecting, but probably the
measurement is ok and the fixed losses due to the other elements were
somewhat overestimated during the design, and the gain of the amplifier
that is in the noise path is a bit higher than expected. I will measure
directly at the noise source output, and check losses and amplifier
gain, but to have a bit more of noise available is not a problem in this
case (in fact, it is an advantage). Mainly I was looking to be sure that
I was measuring it in the right way, so thank you very much for your help.
Best regards,
Javier, EA1CRB
JH
Javier Herrero
Sat, Oct 22, 2011 7:21 PM
El 22/10/2011 16:49, Graham / KE9H escribió:
Javier:
When you say your Spectrum Analyzer bandwidth is set to 1 MHz, do you
mean the frequency span width of the screen?
I would think that your receiver bandwidth is the Video Bandwidth,
therefore 1 kHz.
Correction for noise bandwidth is an adjustment for power,
proportional to
bandwidth, therefore 10log(BW1/BW2)
Correcting 1 KHz to 1 Hz is therefore a 30 dB adjustment, not a 60 dB
adjustment.
I think what you are measuring is more like -75dBm/Hz.
No, with 1MHz bandwidth I mean the IF filter bandwidth, not the span.
The 1kHz video filter processes the detected output, so it has no
effect, other than to make the measurement less noisy. When changing the
video bandwidth to 10kHz or 100Hz, the measurement of the noise does not
change, however modifying the IF bandwidth to 100kHz, the measurement
drops 10dB, as expected.
Regards,
Javier, EA1CRB
El 22/10/2011 16:49, Graham / KE9H escribió:
>
>
> Javier:
>
> When you say your Spectrum Analyzer bandwidth is set to 1 MHz, do you
> mean the frequency span width of the screen?
>
> I would think that your receiver bandwidth is the Video Bandwidth,
> therefore 1 kHz.
> Correction for noise bandwidth is an adjustment for power,
> proportional to
> bandwidth, therefore 10log(BW1/BW2)
>
> Correcting 1 KHz to 1 Hz is therefore a 30 dB adjustment, not a 60 dB
> adjustment.
> I think what you are measuring is more like -75dBm/Hz.
>
>
No, with 1MHz bandwidth I mean the IF filter bandwidth, not the span.
The 1kHz video filter processes the detected output, so it has no
effect, other than to make the measurement less noisy. When changing the
video bandwidth to 10kHz or 100Hz, the measurement of the noise does not
change, however modifying the IF bandwidth to 100kHz, the measurement
drops 10dB, as expected.
Regards,
Javier, EA1CRB
