Noise Floor
Hi
The amplifier board was sitting in mid air with no shielding. Stray pickup from who
knows where is a possibility.
Bob
On Mar 25, 2020, at 6:32 PM, John Miles john@miles.io wrote:
-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@lists.febo.com] On Behalf Of
kb8tq@n1k.org
Sent: Wednesday, March 25, 2020 9:46 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Noise Floor
Phase noise looks pretty good. ADEV has some weird "stuff" going on. Time
to start tearing the board apart to see what's wrong with it?
Maybe there's some noise in those resistors .... let's go !!!!
Resistor noise won't normally show up on plots at this level, but it does look like there is some kind of periodic disturbance near 1 Hz. Could be a thermal artifact due to convection currents on the board, or possibly a case where large undamped LC components have been used in a power supply filter or bias network.
I'd be more likely to suspect crosstalk from a nearby 5 MHz source that isn't quite on the same frequency, which should be easy enough to rule out. Poor cable shield integrity can also encourage this type of artifact to appear, even in the absence of an obvious interferer.
On the phase noise plot, the 53100A thinks it's an instrument spur and is removing it. It's very unlikely to be one, but this process will never be 100% reliable, especially in short-duration measurements. You can see a suspiciously-flat segment centered at about 0.9 Hz, which often indicates that a spur is being suppressed automatically. The stability data doesn't undergo any automatic spur detection or removal, so when you see ripple in the ADEV plot that doesn't correspond to an obvious spur on the PN plot, it's a good idea to either let the measurement run longer or set the 'Spur min offset' value to 10 Hz or so.
-- john
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Hi
Ok so here's a "new" part as opposed to one that is many decades old. Again
this is a part that has been talked about
more than once on the list. The demo board is an early one, but I assume it
is representative of how the CMOS output
part you get today works.
There are two runs. The first pretty clearly shows the part warming up. The
second still shows temperature effects,
they just are not as obvious. If you really need to hit < 1x10^-15 at 100
seconds with this part, drafts are not a good thing.
The part is being driven with 4 dbm at 5 MHz. Max input is rated as 10 dbm
so that's not as nutty as it sounds. 5 MHz ( or
even 10 MHz) is well below the design target for this part. There's not a
lot on the datasheet to compare to. As with the previous
part, ADEV is pretty good (out to 100 sec). Phase noise is not in the 10811
class wideband. If you need low wideband phase noise
as a logic signal at 5 MHz, you need to do something different. For ADEV,
this will do just fine.
Bob
-----Original Message-----
From: time-nuts time-nuts-bounces@lists.febo.com On Behalf Of Charles
Steinmetz
Sent: Wednesday, March 25, 2020 5:23 PM
To: time-nuts@lists.febo.com
Subject: Re: [time-nuts] Noise Floor
Taka Kamiya wrote:
I've been playing around with Clifton amplifier as well. Mine, input is
terminated with 50 ohm register, and rest is unmodified, so it has 6dB gain.
I have a 10dB pad on input side. I, too, noticed there will be a severe
clipping with driving it too hard. * * * I with there was a little
more room there....
Bob wrote:
Maybe there's some noise in those resistors
Well..... maybe not so much.
If you drive this board so it has a couple db more output, it goes into
clipping. When that happens .... yuck.
Noise and ADEV both are massively impacted.
You very much do not want to overdrive this board. * * *
I would stick with 12 dbm or less
You can buy some headroom by raising the supply voltage. There is an
on-card LM78L09 9v voltage regulator (U902) that can safely be raised to
12v (LM78L12). This will get you cleanly to and a bit past the
traditional +13 dBm (1v rms) standard reference level. Of course, you
will need to make sure the raw supply voltage is >15v.
As to noise, the 200 ohm resistor on the opamp's noninverting input
(R901) accounts for nearly 6dB of the amplifier noise (assuming an
effective source impedance of 50 ohms). Reducing this to, say, 33 ohms
will lower the noise floor a few dB.
Finally, the state of CFB video amplifier development has advanced
dramatically in the 20 years since the AD8007 was introduced. New
amplifiers with supply voltage ratings up to 36v are available (allowing
about 10dB greater headroom than the 8007), and many of the newer opamps
clip much more gracefully than the 8007 when you do hit the limit (but
you really want not to do that in any measurement application).
Many of these new CFB amplifiers have been discussed here on the list,
and each has its own fans. One I like that doesn't get mentioned much
is the LME49713. It is discontinued, but still available from Rochester
Electronics and others. But there are lots of good choices.
Best regards,
Charles
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According to the datasheet, AD8007's absolute max is 12.5V. It's a bit scary to go to 12V. I was able to reduce the gain to zero dB, and get a clean and respectable 11.5dBm output. With this, I'm perfectly happy. I would experiment with other changes if I had a meaningful way to measure its impact, but I do not.
Thanks for your advice!
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
On Wednesday, March 25, 2020, 5:28:16 PM EDT, Charles Steinmetz <csteinmetz@yandex.com> wrote:
Taka Kamiya wrote:
I've been playing around with Clifton amplifier as well. Mine, input is terminated with 50 ohm register, and rest is unmodified, so it has 6dB gain. I have a 10dB pad on input side. I, too, noticed there will be a severe clipping with driving it too hard. * * * I with there was a little more room there....
Bob wrote:
Maybe there's some noise in those resistors
Well..... maybe not so much.
If you drive this board so it has a couple db more output, it goes into clipping. When that happens .... yuck.
Noise and ADEV both are massively impacted.
You very much do not want to overdrive this board. * * *
I would stick with 12 dbm or less
You can buy some headroom by raising the supply voltage. There is an
on-card LM78L09 9v voltage regulator (U902) that can safely be raised to
12v (LM78L12). This will get you cleanly to and a bit past the
traditional +13 dBm (1v rms) standard reference level. Of course, you
will need to make sure the raw supply voltage is >15v.
As to noise, the 200 ohm resistor on the opamp's noninverting input
(R901) accounts for nearly 6dB of the amplifier noise (assuming an
effective source impedance of 50 ohms). Reducing this to, say, 33 ohms
will lower the noise floor a few dB.
Finally, the state of CFB video amplifier development has advanced
dramatically in the 20 years since the AD8007 was introduced. New
amplifiers with supply voltage ratings up to 36v are available (allowing
about 10dB greater headroom than the 8007), and many of the newer opamps
clip much more gracefully than the 8007 when you do hit the limit (but
you really want not to do that in any measurement application).
Many of these new CFB amplifiers have been discussed here on the list,
and each has its own fans. One I like that doesn't get mentioned much
is the LME49713. It is discontinued, but still available from Rochester
Electronics and others. But there are lots of good choices.
Best regards,
Charles
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
Taka Kamiya wrote:
According to the datasheet, AD8007's absolute max is 12.5V. It's a bit scary to go to 12V.
Not at all. Look at the first page of the datasheet, which recommends
supplies from 5v to 12v. I've deployed thousands of them running at 12v
(usually, +/- 6v) with superb reliability.
That said, today I use modern CFB amps with 36v supply ratings for these
jobs, and if I had a Z10000 I would certainly retrofit it with one
without a second thought. There is no substitute for headroom!
Best regards,
Charles
The PN floor is somewhat lower with a 15dBm rather than a 4dBm input
http://www.ko4bb.com/getsimple/index.php?id=phase-noise-and-other-measurements-with-a-timepod
Bruce
On 27 March 2020 at 06:11 kb8tq@n1k.org mailto:kb8tq@n1k.org wrote:
Hi
Ok so here's a "new" part as opposed to one that is many decades old. Again
this is a part that has been talked about
more than once on the list. The demo board is an early one, but I assume it
is representative of how the CMOS output
part you get today works.
There are two runs. The first pretty clearly shows the part warming up. The
second still shows temperature effects,
they just are not as obvious. If you *really* need to hit < 1x10^-15 at 100
seconds with this part, drafts are not a good thing.
The part is being driven with 4 dbm at 5 MHz. Max input is rated as 10 dbm
so that's not as nutty as it sounds. 5 MHz ( or
even 10 MHz) is well below the design target for this part. There's not a
lot on the datasheet to compare to. As with the previous
part, ADEV is pretty good (out to 100 sec). Phase noise is not in the 10811
class wideband. If you need low wideband phase noise
as a logic signal at 5 MHz, you need to do something different. For ADEV,
this will do just fine.
Bob
-----Original Message-----
From: time-nuts <time-nuts-bounces@lists.febo.com mailto:time-nuts-bounces@lists.febo.com > On Behalf Of Charles
Steinmetz
Sent: Wednesday, March 25, 2020 5:23 PM
To: time-nuts@lists.febo.com mailto:time-nuts@lists.febo.com
Subject: Re: [time-nuts] Noise Floor
Taka Kamiya wrote:
I've been playing around with Clifton amplifier as well. Mine, input is
terminated with 50 ohm register, and rest is unmodified, so it has 6dB gain.
I have a 10dB pad on input side. I, too, noticed there will be a severe
clipping with driving it too hard. * * * I with there was a little
more room there....
Bob wrote:
Maybe there's some noise in those resistors
Well..... maybe not so much.
If you drive this board so it has a couple db more output, it goes into
clipping. When that happens .... yuck.
Noise and ADEV both are massively impacted.
You very much do not want to overdrive this board. * * *
I would stick with 12 dbm or less
You can buy some headroom by raising the supply voltage. There is an
on-card LM78L09 9v voltage regulator (U902) that can safely be raised to
12v (LM78L12). This will get you cleanly to and a bit past the
traditional +13 dBm (1v rms) standard reference level. Of course, you
will need to make sure the raw supply voltage is >15v.
As to noise, the 200 ohm resistor on the opamp's noninverting input
(R901) accounts for nearly 6dB of the amplifier noise (assuming an
effective source impedance of 50 ohms). Reducing this to, say, 33 ohms
will lower the noise floor a few dB.
Finally, the state of CFB video amplifier development has advanced
dramatically in the 20 years since the AD8007 was introduced. New
amplifiers with supply voltage ratings up to 36v are available (allowing
about 10dB greater headroom than the 8007), and many of the newer opamps
clip much more gracefully than the 8007 when you do hit the limit (but
you really want not to do that in any measurement application).
Many of these new CFB amplifiers have been discussed here on the list,
and each has its own fans. One I like that doesn't get mentioned much
is the LME49713. It is discontinued, but still available from Rochester
Electronics and others. But there are lots of good choices.
Best regards,
Charles
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Yes. The first page says that, along with several entries in the spec sheet. Then, on page 6 lists absolute maximum. 12.6V (I was .1V off). To me, that's awfully close. I chose not to go there, especially when 9V gave me what I wanted in the first place.
In many ways and places, I've learned not to get too close to the maximum rating of devices.
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
On Thursday, March 26, 2020, 4:48:25 PM EDT, Charles Steinmetz <csteinmetz@yandex.com> wrote:
Taka Kamiya wrote:
According to the datasheet, AD8007's absolute max is 12.5V. It's a bit scary to go to 12V.
Not at all. Look at the first page of the datasheet, which recommends
supplies from 5v to 12v. I've deployed thousands of them running at 12v
(usually, +/- 6v) with superb reliability.
That said, today I use modern CFB amps with 36v supply ratings for these
jobs, and if I had a Z10000 I would certainly retrofit it with one
without a second thought. There is no substitute for headroom!
Best regards,
Charles
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
Hi
So here's an OPA 693 running on the TI demo board. One trace has a 50 ohm
termination on the
input. The other trace has no termination. Yes that's not the best way to
run a splitter. Input signal
level to the splitter is same / same for both runs.
No big surprise, phase noise is almost 6 db better. ADEV is still doing
pretty well. It and the phase
are impacted by something at the longer tau's. Is it the mixer and
temperature? Is it the sun going
down and things cooling off? Not at all clear. The main point is that the
termination isn't helping
the phase noise any. Throw away a resistor and nose goes down by 5 db ....
Bob
-----Original Message-----
From: time-nuts time-nuts-bounces@lists.febo.com On Behalf Of Bruce
Griffiths
Sent: Thursday, March 26, 2020 5:01 PM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Subject: Re: [time-nuts] Noise Floor
The PN floor is somewhat lower with a 15dBm rather than a 4dBm input
http://www.ko4bb.com/getsimple/index.php?id=phase-noise-and-other-measuremen
ts-with-a-timepod
Bruce
On 27 March 2020 at 06:11 kb8tq@n1k.org mailto:kb8tq@n1k.org wrote:
Hi
Ok so here's a "new" part as opposed to one that is many decades old.
Again
this is a part that has been talked about
more than once on the list. The demo board is an early one, but I
assume it
is representative of how the CMOS output
part you get today works.
There are two runs. The first pretty clearly shows the part warming
up. The
second still shows temperature effects,
they just are not as obvious. If you *really* need to hit < 1x10^-15
at 100
seconds with this part, drafts are not a good thing.
The part is being driven with 4 dbm at 5 MHz. Max input is rated as 10
dbm
so that's not as nutty as it sounds. 5 MHz ( or
even 10 MHz) is well below the design target for this part. There's
not a
lot on the datasheet to compare to. As with the previous
part, ADEV is pretty good (out to 100 sec). Phase noise is not in the
10811
class wideband. If you need low wideband phase noise
as a logic signal at 5 MHz, you need to do something different. For
ADEV,
this will do just fine.
Bob
-----Original Message-----
From: time-nuts <time-nuts-bounces@lists.febo.com
mailto:time-nuts-bounces@lists.febo.com > On Behalf Of Charles
Steinmetz
Sent: Wednesday, March 25, 2020 5:23 PM
To: time-nuts@lists.febo.com mailto:time-nuts@lists.febo.com
Subject: Re: [time-nuts] Noise Floor
Taka Kamiya wrote:
I've been playing around with Clifton amplifier as well. Mine,
input is
terminated with 50 ohm register, and rest is unmodified, so it has
6dB gain.
I have a 10dB pad on input side. I, too, noticed there will be a
severe
clipping with driving it too hard. * * * I with there was a little
more room there....
Bob wrote:
Maybe there's some noise in those resistors
Well..... maybe not so much.
If you drive this board so it has a couple db more output, it goes
into
clipping. When that happens .... yuck.
Noise and ADEV both are massively impacted.
You very much do not want to overdrive this board. * * *
I would stick with 12 dbm or less
You can buy some headroom by raising the supply voltage. There is an
on-card LM78L09 9v voltage regulator (U902) that can safely be raised
to
12v (LM78L12). This will get you cleanly to and a bit past the
traditional +13 dBm (1v rms) standard reference level. Of course, you
will need to make sure the raw supply voltage is >15v.
As to noise, the 200 ohm resistor on the opamp's noninverting input
(R901) accounts for nearly 6dB of the amplifier noise (assuming an
effective source impedance of 50 ohms). Reducing this to, say, 33 ohms
will lower the noise floor a few dB.
Finally, the state of CFB video amplifier development has advanced
dramatically in the 20 years since the AD8007 was introduced. New
amplifiers with supply voltage ratings up to 36v are available
(allowing
about 10dB greater headroom than the 8007), and many of the newer
opamps
clip much more gracefully than the 8007 when you do hit the limit (but
you really want not to do that in any measurement application).
Many of these new CFB amplifiers have been discussed here on the list,
and each has its own fans. One I like that doesn't get mentioned much
is the LME49713. It is discontinued, but still available from
Rochester
Electronics and others. But there are lots of good choices.
Best regards,
Charles
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mailto:time-nuts@lists.febo.com
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