A new member & PN test set
Hi list,
I am in a process of making a low noise frequency synthesizer for the 1st LO
for my new DSP HF transceiver (http://neon.skydan.in.ua). This list is not
directly related to my project, but I found a lot of useful information in
this list - thanks for all contributors!
I see a discussion regarding "$40 phase noise test set". I have built one
and
already use it for several months. It is a great help in design process (I
am not "blind" anymore :) ). If somebody is interested I can share all the
information about it.
Best wishes!
Oleg
On Sun, Mar 27, 2016 at 11:25:36PM +0300, Oleg Skydan wrote:
Hi list,
I am in a process of making a low noise frequency
synthesizer for the 1st LO for my new DSP HF transceiver
(http://neon.skydan.in.ua). This list is not directly
related to my project, but I found a lot of useful
information in this list - thanks for all contributors!
I see a discussion regarding "$40 phase noise test set".
I have built one and already use it for several months.
It is a great help in design process (I am not "blind"
anymore :) ).
If somebody is interested I can share all the infor-
mation about it.
Yes, please do! I'm interested!
Thanks,
Herbert
Best wishes!
Oleg
time-nuts mailing list -- time-nuts@febo.com
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https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Hi Oleg,
Welcome. As always, it's a combination of tools, experiments and theory
which over a number of iterations develops into skills. You will notice
that there is quite a bit of hams here too, some just forget to give
their signals.
73 de SA0MAD Magnus
On 03/27/2016 10:25 PM, Oleg Skydan wrote:
Hi list,
I am in a process of making a low noise frequency synthesizer for the
1st LO
for my new DSP HF transceiver (http://neon.skydan.in.ua). This list is not
directly related to my project, but I found a lot of useful information in
this list - thanks for all contributors!
I see a discussion regarding "$40 phase noise test set". I have built
one and
already use it for several months. It is a great help in design process (I
am not "blind" anymore :) ). If somebody is interested I can share all the
information about it.
Best wishes!
Oleg
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.
Yes interested in what you are doing as to measuring phase noise. Rob, NC0B
Sent from my iPad
On Mar 28, 2016, at 3:01 AM, "Oleg Skydan" olegskydan@gmail.com wrote:
Hi list,
I am in a process of making a low noise frequency synthesizer for the 1st LO
for my new DSP HF transceiver (http://neon.skydan.in.ua). This list is not
directly related to my project, but I found a lot of useful information in
this list - thanks for all contributors!
I see a discussion regarding "$40 phase noise test set". I have built one and
already use it for several months. It is a great help in design process (I
am not "blind" anymore :) ). If somebody is interested I can share all the
information about it.
Best wishes!
Oleg
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.
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If this email is spam, report it to
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Hi Oleg, I'd be interested in seeing more information about your phase noise measurement setup.
All the best
Mark Spencer
VE7AFZ
Sent from my iPhone
On Mar 27, 2016, at 1:25 PM, Oleg Skydan olegskydan@gmail.com wrote:
Hi list,
I am in a process of making a low noise frequency synthesizer for the 1st LO
for my new DSP HF transceiver (http://neon.skydan.in.ua). This list is not
directly related to my project, but I found a lot of useful information in
this list - thanks for all contributors!
I see a discussion regarding "$40 phase noise test set". I have built one and
already use it for several months. It is a great help in design process (I
am not "blind" anymore :) ). If somebody is interested I can share all the
information about it.
Best wishes!
Oleg
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.
Hi Oleg,
" If somebody is interested I can share all the information about it. "
Yes I would be very interested to see your phase noise test at least the
principle
73
KJ6UHN
Alex
On 3/28/2016 6:49 AM, Magnus Danielson wrote:
Hi Oleg,
Welcome. As always, it's a combination of tools, experiments and
theory which over a number of iterations develops into skills. You
will notice that there is quite a bit of hams here too, some just
forget to give their signals.
73 de SA0MAD Magnus
On 03/27/2016 10:25 PM, Oleg Skydan wrote:
Hi list,
I am in a process of making a low noise frequency synthesizer for the
1st LO
for my new DSP HF transceiver (http://neon.skydan.in.ua). This list
is not
directly related to my project, but I found a lot of useful
information in
this list - thanks for all contributors!
I see a discussion regarding "$40 phase noise test set". I have built
one and
already use it for several months. It is a great help in design
process (I
am not "blind" anymore :) ). If somebody is interested I can share
all the
information about it.
Best wishes!
Oleg
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.
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.
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.7497 / Virus Database: 4545/11905 - Release Date:
03/28/16
Hi, everybody!
OK. Let's start. Here is the schematics of the "test set"
http://skydan.in.ua/PNTestSet/PN%20Test%20set.pdf . It consists of three
small
boards:
- Mixer board - a simple mixer (500MHz ADE-1+) with 200kHz pi-LPF at the
mixer output. - LNA board - a non-inverting low noise AF amplifier based on AD797 with
switchable 20/40dB gain. - PLL board - contains two TL071 OP amps. One is inverting amplifier, the
other is PLL integrator. The R4,R8,R2,R7,C8 sets the PLL parameters - gain,
passband and damping factor. Loop parameters are also dependent of signal
levels and VCO tuning sensitivity. So you may need to correct them if your
setup differs from mine - VCXO's I use have tuning sensitivity approx
100Hz/V and I set RF level at mixer near 0dBm with LO level near +7dBm. If
you want to build universal test set you will need to use some switchs to
allow setting different loop parameters (I just use my soldering iron and
change parts if needed :) ).
The power supply is a simple design based on 7812/7912 regulators.
I use the E-MU 0202 USB external sound card and laptop PC as the AF spectrum
analyzer.
You will also need some cables. Different fixed attenuators or switchable
one will be also helpful.
I also have several homemade low noise VCXOs for some frequencies (7MHz,
10MHz, 14.318MHz, 60MHz) which I use as the reference signal sources to make
measurements at these frequencies.
Another option is to test two identical oscillators (or other signal
sources). Assuming that both signals will have identical phase noise
characteristics we can correct the results by 3dB (or just add 3dB
correction during calibration).
The calibration and use is simple.
- Set LNA gain to 20dB.
- Set the FFT parameters - flattop window, small (2048..4096) points number
and short averaging in SA software. - Connect reference signal to LO mixer port and signal you are going to
test to RF mixer port through the attenuator. Do not close the PLL yet. - Set the beat level a bit less then the sound card full scale using the
attenuator. Check the beat harmonics levels - they should be at least 30dB
lower then the beat level (add more attenuation if harmonics are higher). - Now set the spectrum analyzer calibration so that beat level is at -27dB
if you measure against low noise reference VXCO, or -30dB if you use two
identical oscillators. - Switch the LNA to 40dB gain.
- Set SA software to Blackman window, 131072points/96kHz SR/necessary
averaging, close PLL, wait for the lock, measure the phase noise.
Why I am calibrating to -27/-30dB:
20dB because the LNA gain is 20dB less during the calibration (compared to
measurement time)
1dB because of FFT parameters 96k/131072 = 0.73Hz * 1.73 (Blackman window) =
1.267Hz, 10 log10(1.267) = 1.03dB
6dB is the correction inherent to used calibration method
additional 3dB needed in case of testing identical oscillators.
Now some words about results. The noise floor of this test set depends of
the signals levels, and with the optimal levels it is in -160..-170dBc/Hz
range (depending of the offset from the carrier). It completely satisfies my
needs, better results can be achieved with the higher level mixer and/or
better LNA. I just used parts that I had :).
Here http://skydan.in.ua/PNTestSet/Screen%20(420)-e.png is an example of the
phase noise measurements results of my homemade low noise 60MHz VCXO (two
identical units were measured). The results at the offsets greater then 1kHz
should be corrected cause the oscillators noise is too close to test set
noise (the real oscillator noise is a bit lower then the displayed one). The
test set noise floor and calibration spectrum is also there.
The boards also have other use.
For example I was able to measure my home made 60MHz VCXO harmonic content
http://skydan.in.ua/PNTestSet/Screen%20(414)-e.png using the mixer, LNA
boards and signal generator. I have no spectrum analyzer so it is a big help
to me :).
Power supply noise can be investigated with the LNA board and sound card.
Look at this screen http://skydan.in.ua/PNTestSet/Screen%20(431)-e.png to
see how bad the LDO regulator noise can be and a great difference in noise
with the simple transistor filter (sorry there are a lot of power line noise
pickup - I needed just to quickly check the power supply noise, so did not
pay a lot attention to minimize them).
The low noise VCXOs with the combiner and attenuator can be used to measure
IMD3 of the receiver. If you add the mixer, LNA and signal generator you can
measure the IMD3 of the separate units (mixers, filters, amplifiers and
etc.).
The low noise VCXO can also be used to test reciprocal mixing DR of the
receiver.
Other useful combinations are possible.
If you like I can post the photos of the boards. They a bit ugly :). Every
time I use them I think about mounting them in personal metal boxes, but I
always find something more important to do...
Best wishes,
Oleg
P.S. I am not aware of the attachments rules of this list, so put the links
in the message instead of attaching files. Is it OK? Should I attach files
next time?
That's probably a good example of how not to do it well.
-
The chosen mixer isnt as low noise as the various Minicircuits phase
detectors. -
The 50 ohm load after the filter merely serves to halve the phase detector
gain. The IF port is terminated by a 15nF capacitor at RF and LO frequencies
and their harmonics. This produces a frequency dependent gain, however it will
likely be relatively flat over the sound card bandwidth. -
Saturating both mixer ports increases the phase detector gain substantially
and has the lowest noise -
Cascading the PLL circuitry with the preamp causes interaction between the
Preamp gain settings and the PLL bandwidth. Driving the PLL circuit in
parallel with the preamp input directly from the low pass filtered mixer output
avoids this issue as well as your 0.1x amplifier in the PLL section. -
Another method of calibration is desirable in order to account for
potentially non flat frequency response.
There are a large number of NIST papers on PN measurement including a few on
the effect of mixer IF port terminations. A recent one
(http://tf.boulder.nist.gov/general/pdf/2556.pdf) compares the PN performance
of various mixers used as phase detectors.
An OCXO like the 10811A has an EFC gain of around 0.1Hz/volt.
The PLL bandwidth should ideally be less than 1/10 of the lowest offset
frequency for which the PN is to be measured.
If the system frequency response is measured then the PLL bandwidth can be a
little higher albeit with a reduction is sensitivity and an increase in system
PN at the low offset frequency end of the range.
AS is the PN noise of this test set is far too high to measure the PN of state
of the art OCXOs or indeed most modern OXCOs.
Bruce
On Monday, March 28, 2016 11:04:45 PM Oleg Skydan wrote:
Hi, everybody!
OK. Let's start. Here is the schematics of the "test set"
http://skydan.in.ua/PNTestSet/PN%20Test%20set.pdf . It consists of three
small
boards:
- Mixer board - a simple mixer (500MHz ADE-1+) with 200kHz pi-LPF at the
mixer output. - LNA board - a non-inverting low noise AF amplifier based on AD797 with
switchable 20/40dB gain. - PLL board - contains two TL071 OP amps. One is inverting amplifier, the
other is PLL integrator. The R4,R8,R2,R7,C8 sets the PLL parameters - gain,
passband and damping factor. Loop parameters are also dependent of signal
levels and VCO tuning sensitivity. So you may need to correct them if your
setup differs from mine - VCXO's I use have tuning sensitivity approx
100Hz/V and I set RF level at mixer near 0dBm with LO level near +7dBm. If
you want to build universal test set you will need to use some switchs to
allow setting different loop parameters (I just use my soldering iron and
change parts if needed :) ).
The power supply is a simple design based on 7812/7912 regulators.
I use the E-MU 0202 USB external sound card and laptop PC as the AF spectrum
analyzer.
You will also need some cables. Different fixed attenuators or switchable
one will be also helpful.
I also have several homemade low noise VCXOs for some frequencies (7MHz,
10MHz, 14.318MHz, 60MHz) which I use as the reference signal sources to make
measurements at these frequencies.
Another option is to test two identical oscillators (or other signal
sources). Assuming that both signals will have identical phase noise
characteristics we can correct the results by 3dB (or just add 3dB
correction during calibration).
The calibration and use is simple.
- Set LNA gain to 20dB.
- Set the FFT parameters - flattop window, small (2048..4096) points number
and short averaging in SA software. - Connect reference signal to LO mixer port and signal you are going to
test to RF mixer port through the attenuator. Do not close the PLL yet. - Set the beat level a bit less then the sound card full scale using the
attenuator. Check the beat harmonics levels - they should be at least 30dB
lower then the beat level (add more attenuation if harmonics are higher). - Now set the spectrum analyzer calibration so that beat level is at -27dB
if you measure against low noise reference VXCO, or -30dB if you use two
identical oscillators. - Switch the LNA to 40dB gain.
- Set SA software to Blackman window, 131072points/96kHz SR/necessary
averaging, close PLL, wait for the lock, measure the phase noise.
Why I am calibrating to -27/-30dB:
20dB because the LNA gain is 20dB less during the calibration (compared to
measurement time)
1dB because of FFT parameters 96k/131072 = 0.73Hz * 1.73 (Blackman window) =
1.267Hz, 10 log10(1.267) = 1.03dB
6dB is the correction inherent to used calibration method
additional 3dB needed in case of testing identical oscillators.
Now some words about results. The noise floor of this test set depends of
the signals levels, and with the optimal levels it is in -160..-170dBc/Hz
range (depending of the offset from the carrier). It completely satisfies my
needs, better results can be achieved with the higher level mixer and/or
better LNA. I just used parts that I had :).
Here http://skydan.in.ua/PNTestSet/Screen%20(420)-e.png is an example of the
phase noise measurements results of my homemade low noise 60MHz VCXO (two
identical units were measured). The results at the offsets greater then
1kHz should be corrected cause the oscillators noise is too close to test
set noise (the real oscillator noise is a bit lower then the displayed
one). The test set noise floor and calibration spectrum is also there.
The boards also have other use.
For example I was able to measure my home made 60MHz VCXO harmonic content
http://skydan.in.ua/PNTestSet/Screen%20(414)-e.png using the mixer, LNA
boards and signal generator. I have no spectrum analyzer so it is a big help
to me :).
Power supply noise can be investigated with the LNA board and sound card.
Look at this screen http://skydan.in.ua/PNTestSet/Screen%20(431)-e.png to
see how bad the LDO regulator noise can be and a great difference in noise
with the simple transistor filter (sorry there are a lot of power line noise
pickup - I needed just to quickly check the power supply noise, so did not
pay a lot attention to minimize them).
The low noise VCXOs with the combiner and attenuator can be used to measure
IMD3 of the receiver. If you add the mixer, LNA and signal generator you can
measure the IMD3 of the separate units (mixers, filters, amplifiers and
etc.).
The low noise VCXO can also be used to test reciprocal mixing DR of the
receiver.
Other useful combinations are possible.
If you like I can post the photos of the boards. They a bit ugly :). Every
time I use them I think about mounting them in personal metal boxes, but I
always find something more important to do...
Best wishes,
Oleg
P.S. I am not aware of the attachments rules of this list, so put the links
in the message instead of attaching files. Is it OK? Should I attach files
next time?
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.
Hi Oleg,
I like the simplicity here.
Would not GNUradio be a good platform to encode the calibration stuff a
little more gift-wrapped?
What spectrum-analyzer software do you use? (Just curious)
This simple setup would be useful for many purposes.
Depending on the oscillator, the EFC can need inversion, so I sketched
for a similar design such that I could jumper it for either polarity. In
that design I put the inverter after the integrating op-amp.
Cheers,
Magnus
On 03/28/2016 10:04 PM, Oleg Skydan wrote:
Hi, everybody!
OK. Let's start. Here is the schematics of the "test set"
http://skydan.in.ua/PNTestSet/PN%20Test%20set.pdf . It consists of three
small
boards:
- Mixer board - a simple mixer (500MHz ADE-1+) with 200kHz pi-LPF at
the mixer output. - LNA board - a non-inverting low noise AF amplifier based on AD797
with switchable 20/40dB gain. - PLL board - contains two TL071 OP amps. One is inverting amplifier,
the other is PLL integrator. The R4,R8,R2,R7,C8 sets the PLL parameters
- gain, passband and damping factor. Loop parameters are also dependent
of signal levels and VCO tuning sensitivity. So you may need to correct
them if your setup differs from mine - VCXO's I use have tuning
sensitivity approx 100Hz/V and I set RF level at mixer near 0dBm with LO
level near +7dBm. If you want to build universal test set you will need
to use some switchs to allow setting different loop parameters (I just
use my soldering iron and change parts if needed :) ).
The power supply is a simple design based on 7812/7912 regulators.
I use the E-MU 0202 USB external sound card and laptop PC as the AF
spectrum analyzer.
You will also need some cables. Different fixed attenuators or
switchable one will be also helpful.
I also have several homemade low noise VCXOs for some frequencies (7MHz,
10MHz, 14.318MHz, 60MHz) which I use as the reference signal sources to
make measurements at these frequencies.
Another option is to test two identical oscillators (or other signal
sources). Assuming that both signals will have identical phase noise
characteristics we can correct the results by 3dB (or just add 3dB
correction during calibration).
The calibration and use is simple.
- Set LNA gain to 20dB.
- Set the FFT parameters - flattop window, small (2048..4096) points
number and short averaging in SA software. - Connect reference signal to LO mixer port and signal you are going to
test to RF mixer port through the attenuator. Do not close the PLL yet. - Set the beat level a bit less then the sound card full scale using
the attenuator. Check the beat harmonics levels - they should be at
least 30dB lower then the beat level (add more attenuation if harmonics
are higher). - Now set the spectrum analyzer calibration so that beat level is at
-27dB if you measure against low noise reference VXCO, or -30dB if you
use two identical oscillators. - Switch the LNA to 40dB gain.
- Set SA software to Blackman window, 131072points/96kHz SR/necessary
averaging, close PLL, wait for the lock, measure the phase noise.
Why I am calibrating to -27/-30dB:
20dB because the LNA gain is 20dB less during the calibration (compared
to measurement time)
1dB because of FFT parameters 96k/131072 = 0.73Hz * 1.73 (Blackman
window) = 1.267Hz, 10 log10(1.267) = 1.03dB
6dB is the correction inherent to used calibration method
additional 3dB needed in case of testing identical oscillators.
Now some words about results. The noise floor of this test set depends
of the signals levels, and with the optimal levels it is in
-160..-170dBc/Hz range (depending of the offset from the carrier). It
completely satisfies my needs, better results can be achieved with the
higher level mixer and/or better LNA. I just used parts that I had :).
Here http://skydan.in.ua/PNTestSet/Screen%20(420)-e.png is an example of
the phase noise measurements results of my homemade low noise 60MHz VCXO
(two identical units were measured). The results at the offsets greater
then 1kHz should be corrected cause the oscillators noise is too close
to test set noise (the real oscillator noise is a bit lower then the
displayed one). The test set noise floor and calibration spectrum is
also there.
The boards also have other use.
For example I was able to measure my home made 60MHz VCXO harmonic
content http://skydan.in.ua/PNTestSet/Screen%20(414)-e.png using the
mixer, LNA boards and signal generator. I have no spectrum analyzer so
it is a big help to me :).
Power supply noise can be investigated with the LNA board and sound
card. Look at this screen
http://skydan.in.ua/PNTestSet/Screen%20(431)-e.png to see how bad the
LDO regulator noise can be and a great difference in noise with the
simple transistor filter (sorry there are a lot of power line noise
pickup - I needed just to quickly check the power supply noise, so did
not pay a lot attention to minimize them).
The low noise VCXOs with the combiner and attenuator can be used to
measure IMD3 of the receiver. If you add the mixer, LNA and signal
generator you can measure the IMD3 of the separate units (mixers,
filters, amplifiers and etc.).
The low noise VCXO can also be used to test reciprocal mixing DR of the
receiver.
Other useful combinations are possible.
If you like I can post the photos of the boards. They a bit ugly :).
Every time I use them I think about mounting them in personal metal
boxes, but I always find something more important to do...
Best wishes,
Oleg
P.S. I am not aware of the attachments rules of this list, so put the
links in the message instead of attaching files. Is it OK? Should I
attach files next time?
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.
Inversion of gain isn't required, the system will just lock on the opposite slope of the phase detector output. Level shifting to accommodate different EFC ranges nay be useful however.
Bruce
On Tuesday, 29 March 2016 1:12 PM, Magnus Danielson <magnus@rubidium.dyndns.org> wrote:
Hi Oleg,
I like the simplicity here.
Would not GNUradio be a good platform to encode the calibration stuff a
little more gift-wrapped?
What spectrum-analyzer software do you use? (Just curious)
This simple setup would be useful for many purposes.
Depending on the oscillator, the EFC can need inversion, so I sketched
for a similar design such that I could jumper it for either polarity. In
that design I put the inverter after the integrating op-amp.
Cheers,
Magnus
On 03/28/2016 10:04 PM, Oleg Skydan wrote:
Hi, everybody!
OK. Let's start. Here is the schematics of the "test set"
http://skydan.in.ua/PNTestSet/PN%20Test%20set.pdf . It consists of three
small
boards:
- Mixer board - a simple mixer (500MHz ADE-1+) with 200kHz pi-LPF at
the mixer output. - LNA board - a non-inverting low noise AF amplifier based on AD797
with switchable 20/40dB gain. - PLL board - contains two TL071 OP amps. One is inverting amplifier,
the other is PLL integrator. The R4,R8,R2,R7,C8 sets the PLL parameters
- gain, passband and damping factor. Loop parameters are also dependent
of signal levels and VCO tuning sensitivity. So you may need to correct
them if your setup differs from mine - VCXO's I use have tuning
sensitivity approx 100Hz/V and I set RF level at mixer near 0dBm with LO
level near +7dBm. If you want to build universal test set you will need
to use some switchs to allow setting different loop parameters (I just
use my soldering iron and change parts if needed :) ).
The power supply is a simple design based on 7812/7912 regulators.
I use the E-MU 0202 USB external sound card and laptop PC as the AF
spectrum analyzer.
You will also need some cables. Different fixed attenuators or
switchable one will be also helpful.
I also have several homemade low noise VCXOs for some frequencies (7MHz,
10MHz, 14.318MHz, 60MHz) which I use as the reference signal sources to
make measurements at these frequencies.
Another option is to test two identical oscillators (or other signal
sources). Assuming that both signals will have identical phase noise
characteristics we can correct the results by 3dB (or just add 3dB
correction during calibration).
The calibration and use is simple.
- Set LNA gain to 20dB.
- Set the FFT parameters - flattop window, small (2048..4096) points
number and short averaging in SA software. - Connect reference signal to LO mixer port and signal you are going to
test to RF mixer port through the attenuator. Do not close the PLL yet. - Set the beat level a bit less then the sound card full scale using
the attenuator. Check the beat harmonics levels - they should be at
least 30dB lower then the beat level (add more attenuation if harmonics
are higher). - Now set the spectrum analyzer calibration so that beat level is at
-27dB if you measure against low noise reference VXCO, or -30dB if you
use two identical oscillators. - Switch the LNA to 40dB gain.
- Set SA software to Blackman window, 131072points/96kHz SR/necessary
averaging, close PLL, wait for the lock, measure the phase noise.
Why I am calibrating to -27/-30dB:
20dB because the LNA gain is 20dB less during the calibration (compared
to measurement time)
1dB because of FFT parameters 96k/131072 = 0.73Hz * 1.73 (Blackman
window) = 1.267Hz, 10 log10(1.267) = 1.03dB
6dB is the correction inherent to used calibration method
additional 3dB needed in case of testing identical oscillators.
Now some words about results. The noise floor of this test set depends
of the signals levels, and with the optimal levels it is in
-160..-170dBc/Hz range (depending of the offset from the carrier). It
completely satisfies my needs, better results can be achieved with the
higher level mixer and/or better LNA. I just used parts that I had :).
Here http://skydan.in.ua/PNTestSet/Screen%20(420)-e.png is an example of
the phase noise measurements results of my homemade low noise 60MHz VCXO
(two identical units were measured). The results at the offsets greater
then 1kHz should be corrected cause the oscillators noise is too close
to test set noise (the real oscillator noise is a bit lower then the
displayed one). The test set noise floor and calibration spectrum is
also there.
The boards also have other use.
For example I was able to measure my home made 60MHz VCXO harmonic
content http://skydan.in.ua/PNTestSet/Screen%20(414)-e.png using the
mixer, LNA boards and signal generator. I have no spectrum analyzer so
it is a big help to me :).
Power supply noise can be investigated with the LNA board and sound
card. Look at this screen
http://skydan.in.ua/PNTestSet/Screen%20(431)-e.png to see how bad the
LDO regulator noise can be and a great difference in noise with the
simple transistor filter (sorry there are a lot of power line noise
pickup - I needed just to quickly check the power supply noise, so did
not pay a lot attention to minimize them).
The low noise VCXOs with the combiner and attenuator can be used to
measure IMD3 of the receiver. If you add the mixer, LNA and signal
generator you can measure the IMD3 of the separate units (mixers,
filters, amplifiers and etc.).
The low noise VCXO can also be used to test reciprocal mixing DR of the
receiver.
Other useful combinations are possible.
If you like I can post the photos of the boards. They a bit ugly :).
Every time I use them I think about mounting them in personal metal
boxes, but I always find something more important to do...
Best wishes,
Oleg
P.S. I am not aware of the attachments rules of this list, so put the
links in the message instead of attaching files. Is it OK? Should I
attach files next time?
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and follow the instructions there.
Hi, Bruce,
Thank you for the comments and useful link. Probably you did not understand
the goal and positioning of this "project" and I did not tell the history of
how it was build :)
So, the solely goal of making this "test set" was to assist with the design
of the synthesizer unit for my HF transceiver. The synthesizer PN goals are
to archive PN better then -145..-150dBc/Hz@1kHz offset and better
then -150..-155dBc/Hz@5kHz and farther. So I do not need something perfect
to measure parts of the synthesizer or the complete unit.
Now some words how it was build. Several years ago I experimented with the
voltage regulators and needed to measure their noise. So I made an AD797 LNA
for my soundcard. Later I added the mixer which I used (along with the
signal generator) as a selective meter or primitive spectrum analyzer.
Several months ago I started to work at the synthesizer project, so I needed
PN "test set". I found a board with two TL071 in suitable configuration in
my "junk box" and after several minutes of soldering I had the PLL board :)
Usually I am not a fan of such construction methods, but that time it solved
problem quickly.
- The chosen mixer isnt as low noise as the various Minicircuits phase
detectors.
I just used what I have. There are some very bad things here :( (it is way
out of the list theme), so buying parts (especially ones not widely used) is
not a simple task here. The Minicircuits parts are expensive and exotic
here.
- The 50 ohm load after the filter merely serves to halve the phase
detector
gain. The IF port is terminated by a 15nF capacitor at RF and LO
frequencies
and their harmonics. This produces a frequency dependent gain, however it
will
likely be relatively flat over the sound card bandwidth.
I know it does not terminate mixer correctly, but it is simple and it works.
I tried the termination suggested in the NIST papers (with 50Ohm RF
termination and 1kOhm DC/AF one) with no success - the noise floor of the
"test set" was higher. As for the gain flatness, I checked it - you can see
the results of the quick test here
http://skydan.in.ua/PNTestSet/Screen(432)-e.png (it was 60MHz LO + signal
generator slowly tuned around 60MHz, the SA was set to peak and hold mode).
It completely satisfies my needs.
- Saturating both mixer ports increases the phase detector gain
substantially
and has the lowest noise
In this case the simple and reliable calibration method I use will not work,
cause the mixer output will not be sinusoidal anymore. Another problem is
the signal levels - two good RF LNAs will be needed to amplify signals up to
the necessary levels to saturate mixer.
- Cascading the PLL circuitry with the preamp causes interaction between
the
Preamp gain settings and the PLL bandwidth. Driving the PLL circuit in
parallel with the preamp input directly from the low pass filtered mixer
output
avoids this issue as well as your 0.1x amplifier in the PLL section.
I see no reason to use 20dB preamp gain for measurements (the sound card
noise will have too much influence with this setting), so it useful only for
calibration or the other LNA use (not in PN test set). On the other hand if
the PLL circuit connected to the LNA output we have minimal
components/wires/traces/connections in the most sensitive part of the test
set, so the chance to pick up some external noise is also minimized.
I can add that other good and simple/cheap additions will be the integrator
reset button, two buttons to move integrator in positive or negative
direction manually (to speed up the initial lock in some cases, or shift the
output voltage into the necessary EFC range), potentiometer for the manual
VCO/VCXO frequency control (for the calibration) with the switch to
close/open PLL.
An OCXO like the 10811A has an EFC gain of around 0.1Hz/volt.
The PLL bandwidth should ideally be less than 1/10 of the lowest offset
frequency for which the PN is to be measured.
If the system frequency response is measured then the PLL bandwidth can be
a
little higher albeit with a reduction is sensitivity and an increase in
system
PN at the low offset frequency end of the range.
AS is the PN noise of this test set is far too high to measure the PN of
state
of the art OCXOs or indeed most modern OXCOs.
Ohh... I am not a time nut (or maybe not a time nut YET ;). I did not try to
make something "state of the art" - my goals were/are different (see
earlier).
As for the PLL BW of cause one should be aware what the BW is. In my
measurements the PLL BW is less then 30Hz. I am not interested in PN closer
then 1kHz, so no need for any additional correction of the results.
Much more sophisticated system can be made - better ADC, better LNA, RF LNAs
to push mixer in saturation, better software, two channels with cross
correlation and etc. Or we can even use two high speed ADC and move more
things into digital domain. But it can not be done in one evening and for
the less then $40 ;).
Best wishes!
Oleg
Hi Magnus,
Would not GNUradio be a good platform to encode the calibration stuff a
little more gift-wrapped?
I never used the GNUradio. Basically you can use any SA software/hardware
which has the necessary capabilities.
What spectrum-analyzer software do you use? (Just curious)
It is an old SpectraLAB (which is now as far as I know SpectraPLUS). I also
tried DL4YHF Spectrum Lab - it works, but lacks of logarithmic frequency
scale (or I just did not find how to enable it). I think, from time to time,
about writing specialized software with some special features, but there are
always more important things to do :).
All the best!
Oleg
NIST indicate in several early papers that using 50 ohm in series with a capacitor increases the noise over that achieved by capacitively terminating the IF port at the sum frequency (LO + RF) as you have done. NB the RF and LO port match will be improved somewhat with suitable low value series resistors.
However 50 ohms to ground at the LC filter output shouldn't be necessary.
A somewhat larger value should suffice. Despite assertions by Both minicircuits and Watkins Johnson a mixer connected as a phase detector doesnt act like a current source at the IF output (this is obvious from the plot of the phase detection characteristic as a function of IF port low frequency load resistance on the WJ mixer/PD paper. Also the minicircuits assertion that amplifiers apply a voltage offset to the mixer port that can only be attenuated by a resistor in series with the amplifier input plus a lower value shunt resistance at the output of the IF port LC filter is errant nonsense with an opamp based amplifier.
There should be no problems with a parallel connected Buffer amp driving the PLL circuitry at the LC filter output that's the way Wenzel does it for example.Note that the Wenzel low noise amp can be improved significantly using the same components in a slightly different topology.
NIST have used an RF noise source for calibration and to measure the frequency response.
Bruce
On Wednesday, 30 March 2016 12:12 AM, Oleg Skydan <olegskydan@gmail.com> wrote:
Hi, Bruce,
Thank you for the comments and useful link. Probably you did not understand
the goal and positioning of this "project" and I did not tell the history of
how it was build :)
So, the solely goal of making this "test set" was to assist with the design
of the synthesizer unit for my HF transceiver. The synthesizer PN goals are
to archive PN better then -145..-150dBc/Hz@1kHz offset and better
then -150..-155dBc/Hz@5kHz and farther. So I do not need something perfect
to measure parts of the synthesizer or the complete unit.
Now some words how it was build. Several years ago I experimented with the
voltage regulators and needed to measure their noise. So I made an AD797 LNA
for my soundcard. Later I added the mixer which I used (along with the
signal generator) as a selective meter or primitive spectrum analyzer.
Several months ago I started to work at the synthesizer project, so I needed
PN "test set". I found a board with two TL071 in suitable configuration in
my "junk box" and after several minutes of soldering I had the PLL board :)
Usually I am not a fan of such construction methods, but that time it solved
problem quickly.
- The chosen mixer isnt as low noise as the various Minicircuits phase
detectors.
I just used what I have. There are some very bad things here :( (it is way
out of the list theme), so buying parts (especially ones not widely used) is
not a simple task here. The Minicircuits parts are expensive and exotic
here.
- The 50 ohm load after the filter merely serves to halve the phase
detector
gain. The IF port is terminated by a 15nF capacitor at RF and LO
frequencies
and their harmonics. This produces a frequency dependent gain, however it
will
likely be relatively flat over the sound card bandwidth.
I know it does not terminate mixer correctly, but it is simple and it works..
I tried the termination suggested in the NIST papers (with 50Ohm RF
termination and 1kOhm DC/AF one) with no success - the noise floor of the
"test set" was higher. As for the gain flatness, I checked it - you can see
the results of the quick test here
http://skydan.in.ua/PNTestSet/Screen(432)-e.png (it was 60MHz LO + signal
generator slowly tuned around 60MHz, the SA was set to peak and hold mode).
It completely satisfies my needs.
- Saturating both mixer ports increases the phase detector gain
substantially
and has the lowest noise
In this case the simple and reliable calibration method I use will not work,
cause the mixer output will not be sinusoidal anymore. Another problem is
the signal levels - two good RF LNAs will be needed to amplify signals up to
the necessary levels to saturate mixer.
- Cascading the PLL circuitry with the preamp causes interaction between
the
Preamp gain settings and the PLL bandwidth. Driving the PLL circuit in
parallel with the preamp input directly from the low pass filtered mixer
output
avoids this issue as well as your 0.1x amplifier in the PLL section.
I see no reason to use 20dB preamp gain for measurements (the sound card
noise will have too much influence with this setting), so it useful only for
calibration or the other LNA use (not in PN test set). On the other hand if
the PLL circuit connected to the LNA output we have minimal
components/wires/traces/connections in the most sensitive part of the test
set, so the chance to pick up some external noise is also minimized.
I can add that other good and simple/cheap additions will be the integrator
reset button, two buttons to move integrator in positive or negative
direction manually (to speed up the initial lock in some cases, or shift the
output voltage into the necessary EFC range), potentiometer for the manual
VCO/VCXO frequency control (for the calibration) with the switch to
close/open PLL.
An OCXO like the 10811A has an EFC gain of around 0.1Hz/volt.
The PLL bandwidth should ideally be less than 1/10 of the lowest offset
frequency for which the PN is to be measured.
If the system frequency response is measured then the PLL bandwidth can be
a
little higher albeit with a reduction is sensitivity and an increase in
system
PN at the low offset frequency end of the range.
AS is the PN noise of this test set is far too high to measure the PN of
state
of the art OCXOs or indeed most modern OXCOs.
Ohh... I am not a time nut (or maybe not a time nut YET ;). I did not try to
make something "state of the art" - my goals were/are different (see
earlier).
As for the PLL BW of cause one should be aware what the BW is. In my
measurements the PLL BW is less then 30Hz. I am not interested in PN closer
then 1kHz, so no need for any additional correction of the results.
Much more sophisticated system can be made - better ADC, better LNA, RF LNAs
to push mixer in saturation, better software, two channels with cross
correlation and etc. Or we can even use two high speed ADC and move more
things into digital domain. But it can not be done in one evening and for
the less then $40 ;).
Best wishes!
Oleg
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Hi Oleg
Le 29/03/2016 07:18, Oleg Skydan a écrit :
I also tried DL4YHF Spectrum Lab - it works, but lacks of logarithmic
frequency scale (or I just did not find how to enable it).
Just right-click on the frequency scale, then click on "more ...", and
then tick on "logarithmic" in the "Options for the frequency axis" window.
Simple, isn't it ? o:)
Jean-Louis F6AGR
One hidden issue you don't address is that operation of the 40uH inductor at
frequencies above its parallel resonance may allow substantial RF at the sum
of the LO and RF frequencies to appear at the opamp input.
120MHz at the 797 input will likely lead to RF rectification effects in the
opamp input stage. The resultant offset will create a number of issues
including operation away from the quadrature point.
Unless you use something like a series string of inductors and/or a conical
inductor the first parallel resonance of the 40uH inductor is likely to be
somewhat below 120MHz.
Bruce
On Monday, March 28, 2016 11:04:45 PM Oleg Skydan wrote:
Hi, everybody!
OK. Let's start. Here is the schematics of the "test set"
http://skydan.in.ua/PNTestSet/PN%20Test%20set.pdf . It consists of three
small
boards:
- Mixer board - a simple mixer (500MHz ADE-1+) with 200kHz pi-LPF at the
mixer output. - LNA board - a non-inverting low noise AF amplifier based on AD797 with
switchable 20/40dB gain. - PLL board - contains two TL071 OP amps. One is inverting amplifier, the
other is PLL integrator. The R4,R8,R2,R7,C8 sets the PLL parameters - gain,
passband and damping factor. Loop parameters are also dependent of signal
levels and VCO tuning sensitivity. So you may need to correct them if your
setup differs from mine - VCXO's I use have tuning sensitivity approx
100Hz/V and I set RF level at mixer near 0dBm with LO level near +7dBm. If
you want to build universal test set you will need to use some switchs to
allow setting different loop parameters (I just use my soldering iron and
change parts if needed :) ).
The power supply is a simple design based on 7812/7912 regulators.
I use the E-MU 0202 USB external sound card and laptop PC as the AF spectrum
analyzer.
You will also need some cables. Different fixed attenuators or switchable
one will be also helpful.
I also have several homemade low noise VCXOs for some frequencies (7MHz,
10MHz, 14.318MHz, 60MHz) which I use as the reference signal sources to make
measurements at these frequencies.
Another option is to test two identical oscillators (or other signal
sources). Assuming that both signals will have identical phase noise
characteristics we can correct the results by 3dB (or just add 3dB
correction during calibration).
The calibration and use is simple.
- Set LNA gain to 20dB.
- Set the FFT parameters - flattop window, small (2048..4096) points number
and short averaging in SA software. - Connect reference signal to LO mixer port and signal you are going to
test to RF mixer port through the attenuator. Do not close the PLL yet. - Set the beat level a bit less then the sound card full scale using the
attenuator. Check the beat harmonics levels - they should be at least 30dB
lower then the beat level (add more attenuation if harmonics are higher). - Now set the spectrum analyzer calibration so that beat level is at -27dB
if you measure against low noise reference VXCO, or -30dB if you use two
identical oscillators. - Switch the LNA to 40dB gain.
- Set SA software to Blackman window, 131072points/96kHz SR/necessary
averaging, close PLL, wait for the lock, measure the phase noise.
Why I am calibrating to -27/-30dB:
20dB because the LNA gain is 20dB less during the calibration (compared to
measurement time)
1dB because of FFT parameters 96k/131072 = 0.73Hz * 1.73 (Blackman window) =
1.267Hz, 10 log10(1.267) = 1.03dB
6dB is the correction inherent to used calibration method
additional 3dB needed in case of testing identical oscillators.
Now some words about results. The noise floor of this test set depends of
the signals levels, and with the optimal levels it is in -160..-170dBc/Hz
range (depending of the offset from the carrier). It completely satisfies my
needs, better results can be achieved with the higher level mixer and/or
better LNA. I just used parts that I had :).
Here http://skydan.in.ua/PNTestSet/Screen%20(420)-e.png is an example of the
phase noise measurements results of my homemade low noise 60MHz VCXO (two
identical units were measured). The results at the offsets greater then
1kHz should be corrected cause the oscillators noise is too close to test
set noise (the real oscillator noise is a bit lower then the displayed
one). The test set noise floor and calibration spectrum is also there.
The boards also have other use.
For example I was able to measure my home made 60MHz VCXO harmonic content
http://skydan.in.ua/PNTestSet/Screen%20(414)-e.png using the mixer, LNA
boards and signal generator. I have no spectrum analyzer so it is a big help
to me :).
Power supply noise can be investigated with the LNA board and sound card.
Look at this screen http://skydan.in.ua/PNTestSet/Screen%20(431)-e.png to
see how bad the LDO regulator noise can be and a great difference in noise
with the simple transistor filter (sorry there are a lot of power line noise
pickup - I needed just to quickly check the power supply noise, so did not
pay a lot attention to minimize them).
The low noise VCXOs with the combiner and attenuator can be used to measure
IMD3 of the receiver. If you add the mixer, LNA and signal generator you can
measure the IMD3 of the separate units (mixers, filters, amplifiers and
etc.).
The low noise VCXO can also be used to test reciprocal mixing DR of the
receiver.
Other useful combinations are possible.
If you like I can post the photos of the boards. They a bit ugly :). Every
time I use them I think about mounting them in personal metal boxes, but I
always find something more important to do...
Best wishes,
Oleg
P.S. I am not aware of the attachments rules of this list, so put the links
in the message instead of attaching files. Is it OK? Should I attach files
next time?
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From: "Bruce Griffiths" bruce.griffiths@xtra.co.nz
Sent: Wednesday, March 30, 2016 7:29 AM
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Subject: Re: [time-nuts] Oleg' s PN test Re: A new member & PN test set
One hidden issue you don't address is that operation of the 40uH inductor
at
frequencies above its parallel resonance may allow substantial RF at the
sum
of the LO and RF frequencies to appear at the opamp input.
120MHz at the 797 input will likely lead to RF rectification effects in
the
opamp input stage. The resultant offset will create a number of issues
including operation away from the quadrature point.
Unless you use something like a series string of inductors and/or a
conical
inductor the first parallel resonance of the 40uH inductor is likely to be
somewhat below 120MHz.
Ohhh... I do not like words like "substantial", "much more" and etc. I like
numbers and tests. ;)
So I looked at the Murrata inductors datasheets, and it appeared 40uH
inductor will have SRF in 10MHz region. But it does not mean that pi-LPF
will not work at the higher frequencies. Actually it mean that our LPF will
have response similar to the elliptic filters.
So let's draw the model with the inductor with self resonance at 10MHz and
well at 120MHz and 1MHz to see how bad the response is:
1MHz: http://skydan.in.ua/PNTestSet/1MSRF.png
10MHz: http://skydan.in.ua/PNTestSet/10MSRF.png
120MHz: http://skydan.in.ua/PNTestSet/120MSRF.png
As we can see the RF+LO product will be attenuated more than 60dB in all
cases. So, your comments? Would you like me to measure the RF voltage at the
AD797 input in the real "test set"?
However 50 ohms to ground at the LC filter output shouldn't be necessary.
A somewhat larger value should suffice.
I made some experiments trying to find the optimal value of the resistor at
the LC filter output. The phase detector gain grew along with the resistor
value, but so did the harmonics level. So I needed to apply more attenuation
to the input signal to stay in the linear region. The resulting "test set"
noise floor was almost identical for 50..300Ohm values (300Ohm was a bit
better at offsets grater then 2kHz and a bit worse closer). Large values
noticeably degraded the performance.
I suppose the noise floor can be lowered only if better LNA will be used
(currently the LNA noise dominates the PD noise), or if the levels on the
mixer will be increased (this will require higher level mixer and/or new
calibration routine if the mixer will not be in a linear region).
All the best!
Oleg
The first inductor self resonance is much lower than it need be. EPCOS have a
range of inductors which have a much higher first self resonance frequency.
The other problem is that inductors have several resonances alternating
between parallel and series resonance. In short, your inductor model is
inadequate and gives false predictions. You actually need to measure the filter
response.
Conical inductors are available that are effectively resonance free to 40GHz
but the largest value is around 10uH. In principle one could wind one's own
conical inductor with a larger value, However an iron powder (carbonyl iron -
available from Ukraine at least via ebay) and epoxy mixture. A cone angle of
about 15 degrees appears to be suitable.
Failing that, the classical method is to use a series string of inductors of
increasing value. Even then the various resonances need to be damped.
Lossy Ferrites and resistors can be useful, however one has to be careful not
to increase the noise at frequencies of interest.
Bruce
On Wednesday, March 30, 2016 06:11:51 PM Oleg Skydan wrote:
From: "Bruce Griffiths" bruce.griffiths@xtra.co.nz
Sent: Wednesday, March 30, 2016 7:29 AM
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Subject: Re: [time-nuts] Oleg' s PN test Re: A new member & PN test set
One hidden issue you don't address is that operation of the 40uH inductor
at
frequencies above its parallel resonance may allow substantial RF at the
sum
of the LO and RF frequencies to appear at the opamp input.
120MHz at the 797 input will likely lead to RF rectification effects in
the
opamp input stage. The resultant offset will create a number of issues
including operation away from the quadrature point.
Unless you use something like a series string of inductors and/or a
conical
inductor the first parallel resonance of the 40uH inductor is likely to be
somewhat below 120MHz.
Ohhh... I do not like words like "substantial", "much more" and etc. I like
numbers and tests. ;)
So I looked at the Murrata inductors datasheets, and it appeared 40uH
inductor will have SRF in 10MHz region. But it does not mean that pi-LPF
will not work at the higher frequencies. Actually it mean that our LPF will
have response similar to the elliptic filters.
So let's draw the model with the inductor with self resonance at 10MHz and
well at 120MHz and 1MHz to see how bad the response is:
1MHz: http://skydan.in.ua/PNTestSet/1MSRF.png
10MHz: http://skydan.in.ua/PNTestSet/10MSRF.png
120MHz: http://skydan.in.ua/PNTestSet/120MSRF.png
As we can see the RF+LO product will be attenuated more than 60dB in all
cases. So, your comments? Would you like me to measure the RF voltage at the
AD797 input in the real "test set"?
However 50 ohms to ground at the LC filter output shouldn't be necessary.
A somewhat larger value should suffice.
I made some experiments trying to find the optimal value of the resistor at
the LC filter output. The phase detector gain grew along with the resistor
value, but so did the harmonics level. So I needed to apply more attenuation
to the input signal to stay in the linear region. The resulting "test set"
noise floor was almost identical for 50..300Ohm values (300Ohm was a bit
better at offsets grater then 2kHz and a bit worse closer). Large values
noticeably degraded the performance.
I suppose the noise floor can be lowered only if better LNA will be used
(currently the LNA noise dominates the PD noise), or if the levels on the
mixer will be increased (this will require higher level mixer and/or new
calibration routine if the mixer will not be in a linear region).
All the best!
Oleg
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On Thursday, March 31, 2016 08:20:19 AM Bruce Griffiths wrote:
The first inductor self resonance is much lower than it need be. EPCOS have
a range of inductors which have a much higher first self resonance
frequency.
The other problem is that inductors have several resonances alternating
between parallel and series resonance. In short, your inductor model is
inadequate and gives false predictions. You actually need to measure the
filter response.
Conical inductors are available that are effectively resonance free to 40GHz
but the largest value is around 10uH. In principle one could wind one's own
conical inductor with a larger value, However an iron powder (carbonyl iron
- available from Ukraine at least via ebay) and epoxy mixture
filling/core is required.
A cone angle of about 15 degrees appears to be suitable.
Failing that, the classical method is to use a series string of inductors of
increasing value. Even then the various resonances need to be damped. Lossy
Ferrites and resistors can be useful, however one has to be careful not to
increase the noise at frequencies of interest.
Bruce
Note correction above.
Bruce
Am 30.03.2016 um 21:20 schrieb Bruce Griffiths:
Conical inductors are available that are effectively resonance free to 40GHz
but the largest value is around 10uH. In principle one could wind one's own
conical inductor with a larger value, However an iron powder (carbonyl iron -
available from Ukraine at least via ebay) and epoxy mixture. A cone angle of
about 15 degrees appears to be suitable.
Failing that, the classical method is to use a series string of inductors of
increasing value. Even then the various resonances need to be damped.
Lossy Ferrites and resistors can be useful, however one has to be careful not
to increase the noise at frequencies of interest.
It doesn't take conical inductors to separate the baseband from the
carrier at 10 MHz. The
world existed before Piconics and their conical L patents. Yes, we used
them in our 10 GB/s
fiber optic transceivers, just to see what eye diagrams we could
achieve. But at €38 a pop they
never ever made it into production. It was just too easy to replace them
with somewhat more cent stuff.
A colleague even rolled his own from wire, epoxy glue and ferrite beads
smashed in a mortar.
That looked, hmm, ugly, but performed excellently. Now, you get them
from MCL and Coilcraft.
But for a 10 or 100 MHz lowpass, that's way over the top. Not even if
you are nuts.
regards, Gerhard
You've missed the point which is that:
-
With 10MHz input frequencies the sum frequency is actually 20MHz which is beyond the first resonance of the inductor used.Something better is required. The sum frequency is the largest unwanted component that exits the mixer IF port.
-
Oleg is restricted in what he has available, rolling ones own conical inductor is an option given the iron powder Piconics claim to use is potentially available to him locally.
-
Oleg indicated he'd used the rig to measure PN with 60MHz inputs resulting in a 120MHz sum frequency output placing even more severe band reject requirements on the filter/diplexer.
-
The specified mixer is usable to 500 MHz with resulting sum frequency of 1GHz. If someone were tempted to use it at those frequencies as is the results would be "interesting" to say the least.
Obviously one could select off the shelf components that are satisfactory over a small frequency range or for a particular input frequency of interest.. This means the filter components have to be changed whenever the measurement frequency is changed too much.
However its probably more useful to use a filter that works well over the entire range of frequencies for which the mixer is useful.There are many ways to achieve this.
Thanks for the confirmation that home made conical inductors can work well.
A version that worked from say 1MHz to 1GHz would be very useful.
Another potential problem is injection locking:If the VCXO/OCXO under test has inadequate reverse isolation then this can occur leading one to falsely conclude the VCO/OCXO under test has far better performance than it actually has. In effect the injected signal increases the PLL bandwidth far beyond the intended value.
Using high reverse isolation amplifiers on the mixer / phase detector input ports is one way of ensuring that injection locking doesn't occur.
Bruce
From: Gerhard Hoffmann dk4xp@arcor.de
To: time-nuts@febo.com
Sent: Thursday, 31 March 2016 12:12 PM
Subject: Re: [time-nuts] Oleg' s PN test Re: A new member & PN test set
Am 30.03.2016 um 21:20 schrieb Bruce Griffiths:
Conical inductors are available that are effectively resonance free to 40GHz
but the largest value is around 10uH. In principle one could wind one's own
conical inductor with a larger value, However an iron powder (carbonyl iron -
available from Ukraine at least via ebay) and epoxy mixture. A cone angle of
about 15 degrees appears to be suitable.
Failing that, the classical method is to use a series string of inductors of
increasing value. Even then the various resonances need to be damped.
Lossy Ferrites and resistors can be useful, however one has to be careful not
to increase the noise at frequencies of interest.
It doesn't take conical inductors to separate the baseband from the
carrier at 10 MHz. The
world existed before Piconics and their conical L patents. Yes, we used
them in our 10 GB/s
fiber optic transceivers, just to see what eye diagrams we could
achieve. But at €38 a pop they
never ever made it into production. It was just too easy to replace them
with somewhat more cent stuff.
A colleague even rolled his own from wire, epoxy glue and ferrite beads
smashed in a mortar.
That looked, hmm, ugly, but performed excellently. Now, you get them
from MCL and Coilcraft.
But for a 10 or 100 MHz lowpass, that's way over the top. Not even if
you are nuts.
regards, Gerhard
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