Hello,

Saw the term "IP3" used in discussing sw radios.

Guess I'll never learn if I don't take the risk of showing my ignorance, so:
what does the abbreviation
IP3 stand for, please ?

Also, any info. or rumors re a new JRC 545 type (555 ?) radio coming out
next year ?

Thanks,
Bob

Robert11 wrote:
Hello,

Saw the term "IP3" used in discussing sw radios.

Guess I'll never learn if I don't take the risk of showing my ignorance, so:
what does the abbreviation
IP3 stand for, please ?

Also, any info. or rumors re a new JRC 545 type (555 ?) radio coming out
next year ?

Thanks,
Bob

See:
http://www.holmea.demon.co.uk/FracN/IMD.htm
www.maurymw.com/support/pdfs/5C-043.pdf
http://www.nitehawk.com/sm5bsz/pcdsp/dynmeas.htm
http://www.aoruk.com/comments.htm
Higher, larger number, is better.

Terry

Robert11 wrote:

Hello,

Saw the term "IP3" used in discussing sw radios.

Guess I'll never learn if I don't take the risk of showing my ignorance, so:
what does the abbreviation
IP3 stand for, please ?

Also, any info. or rumors re a new JRC 545 type (555 ?) radio coming out
next year ?

Not sure about a 545 type but there is a rack mount radio coming out:

http://www.universal-radio.com/catal...vr/nrd630.html

dxAce
Michigan
USA

IP3 is a figure of merit for dynamic range of a mixer. As already mentioned,
the higher the number, the better the unit.
Basically, the measurement consists of using three RF generators, with each
RF port generator running through a 6dB attenuator, a low-pass filter,
another 6dB attenuator, and a combiner. The output of the combiner is
connected to the RF port of the mixer under test. The reasons for the 6dB
attenuators are twofold; first of all, they provide 12dB of isolation for
the RF generators that is added to the 25 or so dB isolation that the
combiner already has. This helps to prevent the generators from "talking" to
each other, thus preventing IMD to be generated in this portion of the test
setup. The second reason for these attenuators is to provide a broadband
resistive termination for the low-pass filters, so that they maintain their
design characteristics.
A third RF generator is connected to a 3dB attenuator, a low-pass filter,
and another 3dB attenuator to the LO port of the mixer. The reason for the
3dB attenuators is to provide a wideband resistive termination for the
low-pass filter so that it retains its design characteristics.
The low-pass filters are very important in this test setup, since when the
signals are squared up in the switching function of the mixer under test
harmonics can cause measurement error. Mini-Circuits has a requirement of
at least -65dBc for all harmonics present in the test setup. The 6th and 9th
harmonics can be especially troublesome when making IP2 and I.F. port return
loss measurements.
As far as injection levels, the LO generator is set to the level required to
illuminate this port. For a Level 7 mixer, this would be +7dBm, or 5mW. With
this type of mixer, the level of each tone at the output of the combiner
that is applied to the RF port of the mixer needs to be at least 10dB below
the 1dB compression point of the mixer. Since the 1dB compression point for
a typical Level 7 mixer is abour 0dBm, we would be talking about a maximum
level of -10dBm for each tone. -20dBm would be a little bit better, just to
make sure that you are operating within the linear range of the mixer.
Now that we have the proper test setup, we connect all of this to the mixer,
and we connect the output port, in this case the I.F. port, to a spectrum
analyzer, also making sure that the spectrum analyzer is set up for maximum
dynamic range so that IMD isn't generated in this portion of the test setup.
Your test setup needs to have an IMR at least 10db better than the device
you are measuring, in order to minimize any measurement error.
Use at least 50kHz separation between your input tones that are applied to
the RF port; the reason for this is so that phase noise sidebands from the
RF generators don't cause measurement error.
Taking a look at the spectrum analyzer, you will see five major tones; these
are, the LO, which should be suppressed by around 30dB or more, an upper
sideband tone, a lower sideband tone, and upper sideband and lower sideband
IMD products. These two IMD products are your third order terms.
Next, measure the difference between your upper sideband tone and your upper
sideband 3rd order term. Do the same for your lower sideband terms. This
difference between the desired sideband and the 3rd order term is referred
to as your IMR.
The reason for measuring both of these terms is because oftentimes, one of
these measurements will yield better results.
Choose the worst result when characterizing the mixer.
IP3 is calculated by this method: IP3 = (IMR/2 + Pin), whereby Pin is
defined as the power level at the output of the combiner of only one of the
input tones that are applied to the RF port of the mixer.
Some of the reviewers make this measurement using a 5kHz offset of the RF
generators that are applied to the RF port of the mixer. This measurement is
only valid if the noise sidebands of the generators are run through a very
selective filter, such as a crystal filter. In this case, you need to make
sure that these levels are well below the level where IMD would be generated
in the crystal filter itself; also, too much power can shatter a crystal
filter. If I remember correctly, it would be in the ball park of +10dBm.
I remember when I was testing FM communication systems, the test setup would
be similar, with the exception that the spectrum analyzer wasn't needed and
the LO generator wasn't needed since the actual receiver's LO would be used
in this case.
Now, you still need three generators, this time using a 3-port combiner at
the RF port of the input stage of the receiver.
The two interfering RF port generators would be modulated with a 25%
modulation index. First of all, only the desired signal RF generator would
be switched on, using a level that would provide a 12dB SINAD. This is
equivalent to using a 10dB S/N+N ratio in an AM system or a 5% BER in a
digital system. Next, the second and third generators are switched on,
increasing their levels until a 3dB degradation is noted. Now, these two
generators need to be set to frequencies so that their difference frequency
lands on the desired channel where you are making the measurement. Once
again, you need to do this with upper sideband interferors and lower
sideband interferors, since the rejection will not be symmetrical.
The difference between the levels of your desired signal and your
interfering levels is your IMR. IP3 is calculated in the same manner as
mentioned before.
It is no trivial task when making this kind of measurement. The measurement
itself isn't difficult, but the main thing is to make sure that test setup
created IMD doesn't cause any measurement error. After you do this a few
times, it becomes relatively easy, that is, until you have to characterize a
device such as an RF switch that might have an IP3 of +50dBm. This requires
an IMR in your test setup of at least 110dB. Now, that takes a bit of work!
I hope this long-winded explanation helps.

Pete

"dxAce" wrote in message
...


Robert11 wrote:

Hello,

Saw the term "IP3" used in discussing sw radios.

Guess I'll never learn if I don't take the risk of showing my ignorance,
so:
what does the abbreviation
IP3 stand for, please ?

Also, any info. or rumors re a new JRC 545 type (555 ?) radio coming out
next year ?

Not sure about a 545 type but there is a rack mount radio coming out:

http://www.universal-radio.com/catal...vr/nrd630.html

dxAce
Michigan
USA

Hi,

Helps a lot.
Very clear explanation.

Appreciate it.

Thanks,
Bob
-------------------
"Pete KE9OA" wrote in message
...
IP3 is a figure of merit for dynamic range of a mixer. As already
mentioned, the higher the number, the better the unit.
Basically, the measurement consists of using three RF generators, with
each RF port generator running through a 6dB attenuator, a low-pass
filter, another 6dB attenuator, and a combiner. The output of the combiner
is connected to the RF port of the mixer under test. The reasons for the
6dB attenuators are twofold; first of all, they provide 12dB of isolation
for the RF generators that is added to the 25 or so dB isolation that the
combiner already has. This helps to prevent the generators from "talking"
to each other, thus preventing IMD to be generated in this portion of the
test setup. The second reason for these attenuators is to provide a
broadband resistive termination for the low-pass filters, so that they
maintain their design characteristics.
A third RF generator is connected to a 3dB attenuator, a low-pass filter,
and another 3dB attenuator to the LO port of the mixer. The reason for the
3dB attenuators is to provide a wideband resistive termination for the
low-pass filter so that it retains its design characteristics.
The low-pass filters are very important in this test setup, since when the
signals are squared up in the switching function of the mixer under test
harmonics can cause measurement error. Mini-Circuits has a requirement of
at least -65dBc for all harmonics present in the test setup. The 6th and
9th harmonics can be especially troublesome when making IP2 and I.F. port
return loss measurements.
As far as injection levels, the LO generator is set to the level required
to illuminate this port. For a Level 7 mixer, this would be +7dBm, or 5mW.
With this type of mixer, the level of each tone at the output of the
combiner that is applied to the RF port of the mixer needs to be at least
10dB below the 1dB compression point of the mixer. Since the 1dB
compression point for a typical Level 7 mixer is abour 0dBm, we would be
talking about a maximum level of -10dBm for each tone. -20dBm would be a
little bit better, just to make sure that you are operating within the
linear range of the mixer.
Now that we have the proper test setup, we connect all of this to the
mixer, and we connect the output port, in this case the I.F. port, to a
spectrum analyzer, also making sure that the spectrum analyzer is set up
for maximum dynamic range so that IMD isn't generated in this portion of
the test setup. Your test setup needs to have an IMR at least 10db better
than the device you are measuring, in order to minimize any measurement
error.
Use at least 50kHz separation between your input tones that are applied to
the RF port; the reason for this is so that phase noise sidebands from the
RF generators don't cause measurement error.
Taking a look at the spectrum analyzer, you will see five major tones;
these are, the LO, which should be suppressed by around 30dB or more, an
upper sideband tone, a lower sideband tone, and upper sideband and lower
sideband IMD products. These two IMD products are your third order terms.
Next, measure the difference between your upper sideband tone and your
upper sideband 3rd order term. Do the same for your lower sideband terms.
This difference between the desired sideband and the 3rd order term is
referred to as your IMR.
The reason for measuring both of these terms is because oftentimes, one of
these measurements will yield better results.
Choose the worst result when characterizing the mixer.
IP3 is calculated by this method: IP3 = (IMR/2 + Pin), whereby Pin is
defined as the power level at the output of the combiner of only one of
the input tones that are applied to the RF port of the mixer.
Some of the reviewers make this measurement using a 5kHz offset of the RF
generators that are applied to the RF port of the mixer. This measurement
is only valid if the noise sidebands of the generators are run through a
very selective filter, such as a crystal filter. In this case, you need to
make sure that these levels are well below the level where IMD would be
generated in the crystal filter itself; also, too much power can shatter a
crystal filter. If I remember correctly, it would be in the ball park of
+10dBm.
I remember when I was testing FM communication systems, the test setup
would be similar, with the exception that the spectrum analyzer wasn't
needed and the LO generator wasn't needed since the actual receiver's LO
would be used in this case.
Now, you still need three generators, this time using a 3-port combiner at
the RF port of the input stage of the receiver.
The two interfering RF port generators would be modulated with a 25%
modulation index. First of all, only the desired signal RF generator would
be switched on, using a level that would provide a 12dB SINAD. This is
equivalent to using a 10dB S/N+N ratio in an AM system or a 5% BER in a
digital system. Next, the second and third generators are switched on,
increasing their levels until a 3dB degradation is noted. Now, these two
generators need to be set to frequencies so that their difference
frequency lands on the desired channel where you are making the
measurement. Once again, you need to do this with upper sideband
interferors and lower sideband interferors, since the rejection will not
be symmetrical.
The difference between the levels of your desired signal and your
interfering levels is your IMR. IP3 is calculated in the same manner as
mentioned before.
It is no trivial task when making this kind of measurement. The
measurement itself isn't difficult, but the main thing is to make sure
that test setup created IMD doesn't cause any measurement error. After you
do this a few times, it becomes relatively easy, that is, until you have
to characterize a device such as an RF switch that might have an IP3 of
+50dBm. This requires an IMR in your test setup of at least 110dB. Now,
that takes a bit of work!
I hope this long-winded explanation helps.

Pete

"dxAce" wrote in message
...


Robert11 wrote:

Hello,

Saw the term "IP3" used in discussing sw radios.

Guess I'll never learn if I don't take the risk of showing my ignorance,
so:
what does the abbreviation
IP3 stand for, please ?

Also, any info. or rumors re a new JRC 545 type (555 ?) radio coming out
next year ?

Not sure about a 545 type but there is a rack mount radio coming out:

http://www.universal-radio.com/catal...vr/nrd630.html

dxAce
Michigan
USA

Anytime Bob!

Pete

"Robert11" wrote in message
...
Hi,

Helps a lot.
Very clear explanation.

Appreciate it.

Thanks,
Bob
-------------------
"Pete KE9OA" wrote in message
...
IP3 is a figure of merit for dynamic range of a mixer. As already
mentioned, the higher the number, the better the unit.
Basically, the measurement consists of using three RF generators, with
each RF port generator running through a 6dB attenuator, a low-pass
filter, another 6dB attenuator, and a combiner. The output of the
combiner is connected to the RF port of the mixer under test. The reasons
for the 6dB attenuators are twofold; first of all, they provide 12dB of
isolation for the RF generators that is added to the 25 or so dB
isolation that the combiner already has. This helps to prevent the
generators from "talking" to each other, thus preventing IMD to be
generated in this portion of the test setup. The second reason for these
attenuators is to provide a broadband resistive termination for the
low-pass filters, so that they maintain their design characteristics.
A third RF generator is connected to a 3dB attenuator, a low-pass filter,
and another 3dB attenuator to the LO port of the mixer. The reason for
the 3dB attenuators is to provide a wideband resistive termination for
the low-pass filter so that it retains its design characteristics.
The low-pass filters are very important in this test setup, since when
the signals are squared up in the switching function of the mixer under
test harmonics can cause measurement error. Mini-Circuits has a
requirement of at least -65dBc for all harmonics present in the test
setup. The 6th and 9th harmonics can be especially troublesome when
making IP2 and I.F. port return loss measurements.
As far as injection levels, the LO generator is set to the level required
to illuminate this port. For a Level 7 mixer, this would be +7dBm, or
5mW. With this type of mixer, the level of each tone at the output of the
combiner that is applied to the RF port of the mixer needs to be at least
10dB below the 1dB compression point of the mixer. Since the 1dB
compression point for a typical Level 7 mixer is abour 0dBm, we would be
talking about a maximum level of -10dBm for each tone. -20dBm would be a
little bit better, just to make sure that you are operating within the
linear range of the mixer.
Now that we have the proper test setup, we connect all of this to the
mixer, and we connect the output port, in this case the I.F. port, to a
spectrum analyzer, also making sure that the spectrum analyzer is set up
for maximum dynamic range so that IMD isn't generated in this portion of
the test setup. Your test setup needs to have an IMR at least 10db better
than the device you are measuring, in order to minimize any measurement
error.
Use at least 50kHz separation between your input tones that are applied
to the RF port; the reason for this is so that phase noise sidebands from
the RF generators don't cause measurement error.
Taking a look at the spectrum analyzer, you will see five major tones;
these are, the LO, which should be suppressed by around 30dB or more, an
upper sideband tone, a lower sideband tone, and upper sideband and lower
sideband IMD products. These two IMD products are your third order terms.
Next, measure the difference between your upper sideband tone and your
upper sideband 3rd order term. Do the same for your lower sideband terms.
This difference between the desired sideband and the 3rd order term is
referred to as your IMR.
The reason for measuring both of these terms is because oftentimes, one
of these measurements will yield better results.
Choose the worst result when characterizing the mixer.
IP3 is calculated by this method: IP3 = (IMR/2 + Pin), whereby Pin is
defined as the power level at the output of the combiner of only one of
the input tones that are applied to the RF port of the mixer.
Some of the reviewers make this measurement using a 5kHz offset of the RF
generators that are applied to the RF port of the mixer. This measurement
is only valid if the noise sidebands of the generators are run through a
very selective filter, such as a crystal filter. In this case, you need
to make sure that these levels are well below the level where IMD would
be generated in the crystal filter itself; also, too much power can
shatter a crystal filter. If I remember correctly, it would be in the
ball park of +10dBm.
I remember when I was testing FM communication systems, the test setup
would be similar, with the exception that the spectrum analyzer wasn't
needed and the LO generator wasn't needed since the actual receiver's LO
would be used in this case.
Now, you still need three generators, this time using a 3-port combiner
at the RF port of the input stage of the receiver.
The two interfering RF port generators would be modulated with a 25%
modulation index. First of all, only the desired signal RF generator
would be switched on, using a level that would provide a 12dB SINAD. This
is equivalent to using a 10dB S/N+N ratio in an AM system or a 5% BER in
a digital system. Next, the second and third generators are switched on,
increasing their levels until a 3dB degradation is noted. Now, these two
generators need to be set to frequencies so that their difference
frequency lands on the desired channel where you are making the
measurement. Once again, you need to do this with upper sideband
interferors and lower sideband interferors, since the rejection will not
be symmetrical.
The difference between the levels of your desired signal and your
interfering levels is your IMR. IP3 is calculated in the same manner as
mentioned before.
It is no trivial task when making this kind of measurement. The
measurement itself isn't difficult, but the main thing is to make sure
that test setup created IMD doesn't cause any measurement error. After
you do this a few times, it becomes relatively easy, that is, until you
have to characterize a device such as an RF switch that might have an IP3
of +50dBm. This requires an IMR in your test setup of at least 110dB.
Now, that takes a bit of work!
I hope this long-winded explanation helps.

Pete

"dxAce" wrote in message
...


Robert11 wrote:

Hello,

Saw the term "IP3" used in discussing sw radios.

Guess I'll never learn if I don't take the risk of showing my
ignorance, so:
what does the abbreviation
IP3 stand for, please ?

Also, any info. or rumors re a new JRC 545 type (555 ?) radio coming
out
next year ?

Not sure about a 545 type but there is a rack mount radio coming out:

http://www.universal-radio.com/catal...vr/nrd630.html

dxAce
Michigan
USA

Pete KE9OA wrote:
IP3 is a figure of merit for dynamic range of a mixer. As already mentioned,
the higher the number, the better the unit.
Basically, the measurement consists of using three RF generators, with each
RF port generator running through a 6dB attenuator, a low-pass filter,
another 6dB attenuator, and a combiner. The output of the combiner is
connected to the RF port of the mixer under test. The reasons for the 6dB
attenuators are twofold; first of all, they provide 12dB of isolation for
the RF generators that is added to the 25 or so dB isolation that the
combiner already has. This helps to prevent the generators from "talking" to
each other, thus preventing IMD to be generated in this portion of the test
setup. The second reason for these attenuators is to provide a broadband
resistive termination for the low-pass filters, so that they maintain their
design characteristics.
A third RF generator is connected to a 3dB attenuator, a low-pass filter,
and another 3dB attenuator to the LO port of the mixer. The reason for the
3dB attenuators is to provide a wideband resistive termination for the
low-pass filter so that it retains its design characteristics.
The low-pass filters are very important in this test setup, since when the
signals are squared up in the switching function of the mixer under test
harmonics can cause measurement error. Mini-Circuits has a requirement of
at least -65dBc for all harmonics present in the test setup. The 6th and 9th
harmonics can be especially troublesome when making IP2 and I.F. port return
loss measurements.
As far as injection levels, the LO generator is set to the level required to
illuminate this port. For a Level 7 mixer, this would be +7dBm, or 5mW. With
this type of mixer, the level of each tone at the output of the combiner
that is applied to the RF port of the mixer needs to be at least 10dB below
the 1dB compression point of the mixer. Since the 1dB compression point for
a typical Level 7 mixer is abour 0dBm, we would be talking about a maximum
level of -10dBm for each tone. -20dBm would be a little bit better, just to
make sure that you are operating within the linear range of the mixer.
Now that we have the proper test setup, we connect all of this to the mixer,
and we connect the output port, in this case the I.F. port, to a spectrum
analyzer, also making sure that the spectrum analyzer is set up for maximum
dynamic range so that IMD isn't generated in this portion of the test setup.
Your test setup needs to have an IMR at least 10db better than the device
you are measuring, in order to minimize any measurement error.
Use at least 50kHz separation between your input tones that are applied to
the RF port; the reason for this is so that phase noise sidebands from the
RF generators don't cause measurement error.
Taking a look at the spectrum analyzer, you will see five major tones; these
are, the LO, which should be suppressed by around 30dB or more, an upper
sideband tone, a lower sideband tone, and upper sideband and lower sideband
IMD products. These two IMD products are your third order terms.
Next, measure the difference between your upper sideband tone and your upper
sideband 3rd order term. Do the same for your lower sideband terms. This
difference between the desired sideband and the 3rd order term is referred
to as your IMR.
The reason for measuring both of these terms is because oftentimes, one of
these measurements will yield better results.
Choose the worst result when characterizing the mixer.
IP3 is calculated by this method: IP3 = (IMR/2 + Pin), whereby Pin is
defined as the power level at the output of the combiner of only one of the
input tones that are applied to the RF port of the mixer.
Some of the reviewers make this measurement using a 5kHz offset of the RF
generators that are applied to the RF port of the mixer. This measurement is
only valid if the noise sidebands of the generators are run through a very
selective filter, such as a crystal filter. In this case, you need to make
sure that these levels are well below the level where IMD would be generated
in the crystal filter itself; also, too much power can shatter a crystal
filter. If I remember correctly, it would be in the ball park of +10dBm.
I remember when I was testing FM communication systems, the test setup would
be similar, with the exception that the spectrum analyzer wasn't needed and
the LO generator wasn't needed since the actual receiver's LO would be used
in this case.
Now, you still need three generators, this time using a 3-port combiner at
the RF port of the input stage of the receiver.
The two interfering RF port generators would be modulated with a 25%
modulation index. First of all, only the desired signal RF generator would
be switched on, using a level that would provide a 12dB SINAD. This is
equivalent to using a 10dB S/N+N ratio in an AM system or a 5% BER in a
digital system. Next, the second and third generators are switched on,
increasing their levels until a 3dB degradation is noted. Now, these two
generators need to be set to frequencies so that their difference frequency
lands on the desired channel where you are making the measurement. Once
again, you need to do this with upper sideband interferors and lower
sideband interferors, since the rejection will not be symmetrical.
The difference between the levels of your desired signal and your
interfering levels is your IMR. IP3 is calculated in the same manner as
mentioned before.
It is no trivial task when making this kind of measurement. The measurement
itself isn't difficult, but the main thing is to make sure that test setup
created IMD doesn't cause any measurement error. After you do this a few
times, it becomes relatively easy, that is, until you have to characterize a
device such as an RF switch that might have an IP3 of +50dBm. This requires
an IMR in your test setup of at least 110dB. Now, that takes a bit of work!
I hope this long-winded explanation helps.

Pete



Could you please be more specific? LOL! ; ^ )

Ok, let me
think............................................. ...........Actually, I
can't claim all of this knowledge as my own, especially the troublesome 6th
and 9th harmonics of the LO. I have to give Mr. Lu Chen of Mini-Circuits for
that bit of knowledge.
Mr. Paul Vinsand of Mini-Circuits was nice enough to give me that -65dBc
figure when I was running some tests on a mixer that had a +40dBm IP3. Nice
folks.

Pete

"Somebody Somewhere" wrote in message
ups.com...

Pete KE9OA wrote:
IP3 is a figure of merit for dynamic range of a mixer. As already
mentioned,
the higher the number, the better the unit.
Basically, the measurement consists of using three RF generators, with
each
RF port generator running through a 6dB attenuator, a low-pass filter,
another 6dB attenuator, and a combiner. The output of the combiner is
connected to the RF port of the mixer under test. The reasons for the 6dB
attenuators are twofold; first of all, they provide 12dB of isolation for
the RF generators that is added to the 25 or so dB isolation that the
combiner already has. This helps to prevent the generators from "talking"
to
each other, thus preventing IMD to be generated in this portion of the
test
setup. The second reason for these attenuators is to provide a broadband
resistive termination for the low-pass filters, so that they maintain
their
design characteristics.
A third RF generator is connected to a 3dB attenuator, a low-pass filter,
and another 3dB attenuator to the LO port of the mixer. The reason for
the
3dB attenuators is to provide a wideband resistive termination for the
low-pass filter so that it retains its design characteristics.
The low-pass filters are very important in this test setup, since when
the
signals are squared up in the switching function of the mixer under test
harmonics can cause measurement error. Mini-Circuits has a requirement
of
at least -65dBc for all harmonics present in the test setup. The 6th and
9th
harmonics can be especially troublesome when making IP2 and I.F. port
return
loss measurements.
As far as injection levels, the LO generator is set to the level required
to
illuminate this port. For a Level 7 mixer, this would be +7dBm, or 5mW.
With
this type of mixer, the level of each tone at the output of the combiner
that is applied to the RF port of the mixer needs to be at least 10dB
below
the 1dB compression point of the mixer. Since the 1dB compression point
for
a typical Level 7 mixer is abour 0dBm, we would be talking about a
maximum
level of -10dBm for each tone. -20dBm would be a little bit better, just
to
make sure that you are operating within the linear range of the mixer.
Now that we have the proper test setup, we connect all of this to the
mixer,
and we connect the output port, in this case the I.F. port, to a spectrum
analyzer, also making sure that the spectrum analyzer is set up for
maximum
dynamic range so that IMD isn't generated in this portion of the test
setup.
Your test setup needs to have an IMR at least 10db better than the device
you are measuring, in order to minimize any measurement error.
Use at least 50kHz separation between your input tones that are applied
to
the RF port; the reason for this is so that phase noise sidebands from
the
RF generators don't cause measurement error.
Taking a look at the spectrum analyzer, you will see five major tones;
these
are, the LO, which should be suppressed by around 30dB or more, an upper
sideband tone, a lower sideband tone, and upper sideband and lower
sideband
IMD products. These two IMD products are your third order terms.
Next, measure the difference between your upper sideband tone and your
upper
sideband 3rd order term. Do the same for your lower sideband terms. This
difference between the desired sideband and the 3rd order term is
referred
to as your IMR.
The reason for measuring both of these terms is because oftentimes, one
of
these measurements will yield better results.
Choose the worst result when characterizing the mixer.
IP3 is calculated by this method: IP3 = (IMR/2 + Pin), whereby Pin is
defined as the power level at the output of the combiner of only one of
the
input tones that are applied to the RF port of the mixer.
Some of the reviewers make this measurement using a 5kHz offset of the RF
generators that are applied to the RF port of the mixer. This measurement
is
only valid if the noise sidebands of the generators are run through a
very
selective filter, such as a crystal filter. In this case, you need to
make
sure that these levels are well below the level where IMD would be
generated
in the crystal filter itself; also, too much power can shatter a crystal
filter. If I remember correctly, it would be in the ball park of +10dBm.
I remember when I was testing FM communication systems, the test setup
would
be similar, with the exception that the spectrum analyzer wasn't needed
and
the LO generator wasn't needed since the actual receiver's LO would be
used
in this case.
Now, you still need three generators, this time using a 3-port combiner
at
the RF port of the input stage of the receiver.
The two interfering RF port generators would be modulated with a 25%
modulation index. First of all, only the desired signal RF generator
would
be switched on, using a level that would provide a 12dB SINAD. This is
equivalent to using a 10dB S/N+N ratio in an AM system or a 5% BER in a
digital system. Next, the second and third generators are switched on,
increasing their levels until a 3dB degradation is noted. Now, these two
generators need to be set to frequencies so that their difference
frequency
lands on the desired channel where you are making the measurement. Once
again, you need to do this with upper sideband interferors and lower
sideband interferors, since the rejection will not be symmetrical.
The difference between the levels of your desired signal and your
interfering levels is your IMR. IP3 is calculated in the same manner as
mentioned before.
It is no trivial task when making this kind of measurement. The
measurement
itself isn't difficult, but the main thing is to make sure that test
setup
created IMD doesn't cause any measurement error. After you do this a few
times, it becomes relatively easy, that is, until you have to
characterize a
device such as an RF switch that might have an IP3 of +50dBm. This
requires
an IMR in your test setup of at least 110dB. Now, that takes a bit of
work!
I hope this long-winded explanation helps.

Pete



Could you please be more specific? LOL! ; ^ )

In article ,
"Robert11" wrote:

Hello,

Saw the term "IP3" used in discussing sw radios.

Guess I'll never learn if I don't take the risk of showing my
ignorance, so: what does the abbreviation IP3 stand for, please ?

Also, any info. or rumors re a new JRC 545 type (555 ?) radio coming
out next year ?


IP3 - third order intercept point. That does not mean much to you does
it.

It is a measurement of intermodulation products of two signals. That
probably does not mean much to you either.

Generally it is a measurement of an amplifiers ability to amplify
signals without generating other mixing products. If an amplifier
produces these other mixing products it steals the power from the
signals you are putting at its input limiting the amplification it could
produce on those input signals and so it turns out that IP3 directly
impacts the -1 dB compression point of an amplifier.

The -1 dB compression point is a point where the output of an amplifier
fails to track the input by 1 dB or in other words the gain rolls off 1
dB at some point from what the gain of the amplifier is otherwise.

An intermodulation product is the result of two signals (a mixing
product) that you might be familiar with such as the sum and difference
of two signals. If you took the direct sum or difference then you would
be talking about IP2. This measurement is basically a measure of the
difference of the sum or difference signal (whichever is larger)
compared to the original two signals. A perfect radio circuit would not
produce any other signal mixing products (other than a mixer because the
object of a mixer is to produce the sum and difference signals) so when
it come to IP2 a larger number is better since it is a measure of the
original signal levels (usually the same level for both generators)
compared to the sum and difference signal generated by the amplifier or
whatever circuit the two signals are passing through.

IP3 is the same measurement as IP2 except it is the second harmonic one
one input generator mixed with the sum or difference of the second
generator frequency. Those mixing harmonics levels produced are once
again compared to the original signal levels of the two generators.

To make the measure simple you can set both generators to 0 dB and then
make a measurement of the appropriate mixing products for either IP2 or
IP3. Lets say the IP2 was -66 on the difference and -68 on the plus. The
IP2 would then be 66 dB, which is the worst of the two. Lets say 2 times
generator 1 frequency plus the generator 2 frequency product had the
highest level of -75 dB of the IP3 possibilities. The the IP3 would be
75 dB.

Generally you don't care about IP2 and IP3. This specification only
matters when the radio has to deal with very strong signal levels. Best
example of this in the USA would be local AMBCB stations reducing the
input sensitivity of a radio on short wave or other AMBCB stations.

--
Telamon
Ventura, California

On Mon, 27 Nov 2006 06:02:29 GMT, Telamon
wrote:

In article ,
"Robert11" wrote:

To make the measure simple you can set both generators to 0 dB and then
make a measurement of the appropriate mixing products for either IP2 or
IP3. Lets say the IP2 was -66 on the difference and -68 on the plus. The
IP2 would then be 66 dB, which is the worst of the two. Lets say 2 times
generator 1 frequency plus the generator 2 frequency product had the
highest level of -75 dB of the IP3 possibilities. The the IP3 would be
75 dB.

Wrong. IP3 is a theoretical point in space above a graph. What you
have described is the ratio of a single unwanted product to a desired
signal.