Outch! doggy.Your front feets are like daggrs.Why do you jump up on me
kidney area and pounce on me like that? That hurts.
cuhulin

On Mon, 27 Nov 2006 18:10:13 -0600, wrote:

Outch! doggy.Your front feets are like daggrs.Why do you jump up on me
kidney area and pounce on me like that? That hurts.
cuhulin

Surrealism in its purest form...

In article
,
Telamon wrote:

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.

The IP3 75 dB I stated in the example was not correct. Here is the
general formula: IP(n)= Pin + (delta P/n-1) where if the input power of
tone 1 is used then delta power is the difference of the tone 2 output
power and the inter-mod product power in dBm. If you keep both input
tones at the same level things are easier to calculate so let's say the
amplifier has unity gain and we set up and measure in dBm:

Input tone power (both) -4.0
Output tone power (both) -3.8
(2*F1) - F2 power was -59.7
then the IP3 would be +24

--
Telamon
Ventura, California

This link from Mini-Circuits explains it very clearly, with spectrum
analyzer plots, etc:
http://www.minicircuits.com/pages/pdfs/mxr1-18.pdf
I am not sure about this calculation that is mention here but as an example,
let's consider 0dBm for each tone into the RF port of the mixer under test.
If our IMR (delta) is 60dB, our IP3 will be +30dBm,
since IP3 = [(IMR/2) + Pin]

If we had -4dBm for each tone, using the same mixer as the first example,
the IMR would be 68dB.

If we had -10dBm for each tone, using the same mixer as the first example,
the IMR would be 80dB.

Once again, IP3 is calculated in this manner: IP3 = [(IMR/2) + Pin]

This is the method that Mini-Circuits, Synergy Microwave, Watkins-Johnson,
and other vendors in the industry use when making this calculation. The only
difference is that the term "Delta" us used for the IMR spec. I hadn't heard
of the "IMR" term until I did that stint at Motorola last year.
Take a look at the PDF link, and it will become very clear.
One characteristic of the IP3 terms is that as you increase the level of the
two tones at the input port of the mixer, the 3rd order distortion products
will increase by a 3:1 ratio over the desired tones.
As an example, if you increase your two RF tones by 1dB, your 3rd order
products will increase by 3dB.
3dB increase for each tone will cause a 9dB increase in the 3rd order
products.
This example is only valid if you are operating within the linear range of
the mixer. The linear range is defined as the range where conversion loss
(or conversion gain) is constant as you increase the signal level at the RF
port.
Consider that your typical Level 7 mixer has a conversion loss of 6.5dB.
There will be a point where you will increase your input tones and the
conversion loss will be 7.5dB. This is your 1dB compression point.
Now, the IP2 calculations can get confusing, since there are different
methods of measuring it. The [RFin + (I.F./2)] method is commonly used. With
LO power applied to the mixer under test, a desired frequency is applied to
the RF port.
A measurement of outpur power at the I.F. port is then recorded.
Next, a frequency of [RFin + (I.F./2)] is applied to the RF port. The power
at the I.F. port will now be between 50dB to 80dB below the initial recorded
value. This is your IMR (or Delta).
IP2 is calculated as (IMR + Pin). If your IMR is 70dB and your Pin is 0dBm,
your IP2 is 70dB.
If your IMR is 70dB and
your Pin is -10dBm, your IP3 is 60dB, etc,etc,etc.
I hope this provides further clarification!

Pete

Input tone power (both) -4.0
Output tone power (both) -3.8
(2*F1) - F2 power was -59.7
then the IP3 would be +24

--
Telamon
Ventura, California

In article ,
"Pete KE9OA" wrote:

This link from Mini-Circuits explains it very clearly, with spectrum
analyzer plots, etc:
http://www.minicircuits.com/pages/pdfs/mxr1-18.pdf
I am not sure about this calculation that is mention here but as an example,
let's consider 0dBm for each tone into the RF port of the mixer under test.
If our IMR (delta) is 60dB, our IP3 will be +30dBm,
since IP3 = [(IMR/2) + Pin]

If we had -4dBm for each tone, using the same mixer as the first example,
the IMR would be 68dB.

If we had -10dBm for each tone, using the same mixer as the first example,
the IMR would be 80dB.

Once again, IP3 is calculated in this manner: IP3 = [(IMR/2) + Pin]

This is the method that Mini-Circuits, Synergy Microwave, Watkins-Johnson,
and other vendors in the industry use when making this calculation. The only
difference is that the term "Delta" us used for the IMR spec. I hadn't heard
of the "IMR" term until I did that stint at Motorola last year.
Take a look at the PDF link, and it will become very clear.
One characteristic of the IP3 terms is that as you increase the level of the
two tones at the input port of the mixer, the 3rd order distortion products
will increase by a 3:1 ratio over the desired tones.
As an example, if you increase your two RF tones by 1dB, your 3rd order
products will increase by 3dB.
3dB increase for each tone will cause a 9dB increase in the 3rd order
products.
This example is only valid if you are operating within the linear range of
the mixer. The linear range is defined as the range where conversion loss
(or conversion gain) is constant as you increase the signal level at the RF
port.
Consider that your typical Level 7 mixer has a conversion loss of 6.5dB.
There will be a point where you will increase your input tones and the
conversion loss will be 7.5dB. This is your 1dB compression point.
Now, the IP2 calculations can get confusing, since there are different
methods of measuring it. The [RFin + (I.F./2)] method is commonly used. With
LO power applied to the mixer under test, a desired frequency is applied to
the RF port.
A measurement of outpur power at the I.F. port is then recorded.
Next, a frequency of [RFin + (I.F./2)] is applied to the RF port. The power
at the I.F. port will now be between 50dB to 80dB below the initial recorded
value. This is your IMR (or Delta).
IP2 is calculated as (IMR + Pin). If your IMR is 70dB and your Pin is 0dBm,
your IP2 is 70dB.
If your IMR is 70dB and
your Pin is -10dBm, your IP3 is 60dB, etc,etc,etc.
I hope this provides further clarification!

Pete

Input tone power (both) -4.0
Output tone power (both) -3.8
(2*F1) - F2 power was -59.7
then the IP3 would be +24

The formula I quoted IP(n)= Pin + (delta P/n-1) is a classical
derivation of a 2 tone result in the passband of a broadband circuit
such as an amplifier. Delta P is the difference in the output tone level
and the intermodulation product level. You can use it for the input IP2,
IP3, et etc. The formula can be used to calculate any intermodulation
product as long as the following conditions are met:

1. The tones and intermodulation products you want to make a measurement
on all have to be in the circuits passband.

2. You have to be in the circuits linear range.

3. You have to be within the dynamic range of the measurement equipment.

The Mini-circuits pdf is about a making these measurements on a mixer
and so it requires a third generator as the Lo.

IMR is intermodulation ratio. The definition appears to be the delta of
the input tone level power and the measured spurious response, which is
the intermodulation product I speak of or in other words is a difference
dBc (dB below carrier, this being the input tone). This being the case
then IP3 = Pin + (IMR/2) has the same meaning if there is no gain. If
there is gain then you would get a different answer. I think you are
better off using the formula I referenced as both input power and gain
or loss are accounted for.

The test setup has several amplifiers so I don't know how they actually
expect to make a measurement on the DUT. Also troubling to me that they
state the IP3 measurement can only be made at some input power level and
that it you will get a different result at a different input power
level. Well, you will get the same result at different power levels as
long as you account for it and conditions #2, and #3 above so I don't
understand their problem with that.

They are also using filters. Using filters is OK as long as you don't
violate condition #1 above.

--
Telamon
Ventura, California

Very true on all of your points, but the initial question was about the IP3
of receivers, so the mixer specification is what is being talked about here,
not amplifiers. When characterizing amplifiers, you have either input IP3 or
output IP3 to contend with, so it gets a little bit more complicated.

The formula I quoted IP(n)= Pin + (delta P/n-1) is a classical
derivation of a 2 tone result in the passband of a broadband circuit
such as an amplifier. Delta P is the difference in the output tone level
and the intermodulation product level. You can use it for the input IP2,
IP3, et etc. The formula can be used to calculate any intermodulation
product as long as the following conditions are met:

1. The tones and intermodulation products you want to make a measurement
on all have to be in the circuits passband.

2. You have to be in the circuits linear range.

3. You have to be within the dynamic range of the measurement equipment.

The Mini-circuits pdf is about a making these measurements on a mixer
and so it requires a third generator as the Lo.

IMR is intermodulation ratio. The definition appears to be the delta of
the input tone level power and the measured spurious response, which is
the intermodulation product I speak of or in other words is a difference
dBc (dB below carrier, this being the input tone).

No, we are talking about the delta between the 3rd order product and its
associated tone at the I.F. (output) port of the mixer under test.

This being the case
then IP3 = Pin + (IMR/2) has the same meaning if there is no gain. If
there is gain then you would get a different answer. I think you are
better off using the formula I referenced as both input power and gain
or loss are accounted for.

True.

The test setup has several amplifiers so I don't know how they actually
expect to make a measurement on the DUT.

Actually, this is very easy........those amplifiers have a very high IP3, so
they introduce very low measurement error.
This setup will allow you to have an IMR of at least 110dB. I didn't have
those amplifiers on hand, so I used circulators for the required isolation
when I characterized that MCL digital step attenuator.

Also troubling to me that they
state the IP3 measurement can only be made at some input power level and
that it you will get a different result at a different input power
level. Well, you will get the same result at different power levels as
long as you account for it and conditions #2, and #3 above so I don't
understand their problem with that.

As long as you are within the linear range of the DUT, this is true.

They are also using filters. Using filters is OK as long as you don't
violate condition #1 above.

If you are using low-pass or bandpass filters at the output of each
generator and make sure that the tones are at the required level, this is a
non-issue. Sometimes, you might only have a filter that has a corner
frequency very close to your highest frequency of interest.
Part of calibrating the test setup is making sure that you have the correct
power level at every frequency that you are making the test at. What I would
do is measure the power level of the RF generators and LO generator at every
frequency of interest, and either use a correction factor for setting the
generator output manually, or I would enter the correction factor into the
Labview program when applicable. Since we are making sure that the power
levels are correct at all frequencies, condition #1 is being met.

--
Telamon
Ventura, California

On a final note, I haven't done any multitone testing of
amplifiers..........my tests were limited to harmonic distortion, noise
figure, S-Parameters, and 1dB compression point.
As I have mentioned in the past, it sounds like you have been in the
industry, and I appreciate your input.
One thing I didn't mention was a piece of test equipment that makes these
tests a little bit easier. Instead of using a swept spectrum analyzer, a
Vector Signal Analyzer (VSA) is used. This instrument has a very wide
dynamic range, with a noise floor of -140dBm, even in a very wide passband.
Since this is really an FFT analyzer vs a swept analyzer, you aren't limited
by very long sweep times of the swept analyzer.
Another new tool that has become available from Agilent is the PSA. This is
a spectrum analyzer with added functions, but the best thing about this
analyzer is the very low sideband noise from its internal LO.
This makes it possible to look at the phase noise sidebands from an 8657 for
instance, even at 1MHz away from the carrier.
There were several different generators from Agilent, Rohde and Schwarz, and
Fluke, but the quietest units they had around were still the 8642B. When I
characterized one of those unit at a 100kHz offset, I measured the noise
down at -154dBc.
The new R&S stuff isn't bad, but the 8642 generators are still "king of the
hill".

Pete

In article ,
"Pete KE9OA" wrote:

Very true on all of your points, but the initial question was about
the IP3 of receivers, so the mixer specification is what is being
talked about here, not amplifiers. When characterizing amplifiers,
you have either input IP3 or output IP3 to contend with, so it gets a
little bit more complicated.

The formula I quoted IP(n)= Pin + (delta P/n-1) is a classical
derivation of a 2 tone result in the passband of a broadband
circuit such as an amplifier. Delta P is the difference in the
output tone level and the intermodulation product level. You can
use it for the input IP2, IP3, et etc. The formula can be used to
calculate any intermodulation product as long as the following
conditions are met:

1. The tones and intermodulation products you want to make a
measurement on all have to be in the circuits passband.

2. You have to be in the circuits linear range.

3. You have to be within the dynamic range of the measurement
equipment.

The Mini-circuits pdf is about a making these measurements on a
mixer and so it requires a third generator as the Lo.

IMR is intermodulation ratio. The definition appears to be the
delta of the input tone level power and the measured spurious
response, which is the intermodulation product I speak of or in
other words is a difference dBc (dB below carrier, this being the
input tone).

No, we are talking about the delta between the 3rd order product and
its associated tone at the I.F. (output) port of the mixer under
test.

Maybe that is what you were talking about but I'm trying to stay more
general. The formula and explanation I provided can be applied to RF
circuits in general not just mixers. Mixers comprise just one to three
stages in a radio generally. The rest of the circuits are filters and
amplifiers and detectors. With the right generalized approach you can
analyze any linear circuit or the whole radio.

This being the case then IP3 = Pin + (IMR/2) has the same meaning
if there is no gain. If there is gain then you would get a
different answer. I think you are better off using the formula I
referenced as both input power and gain or loss are accounted for.

True.

The test setup has several amplifiers so I don't know how they
actually expect to make a measurement on the DUT.

Actually, this is very easy........those amplifiers have a very high
IP3, so they introduce very low measurement error. This setup will
allow you to have an IMR of at least 110dB. I didn't have those
amplifiers on hand, so I used circulators for the required isolation
when I characterized that MCL digital step attenuator.

Well, its easy if you know all the specifications of the amplifiers or
have made the measurements on the test setup by itself. This is
something I can't do and would be making an assumption about.

I don't understand why the amplifiers are need in the first place. Maybe
their generators have weak outputs. The test setup is overly complex and
has unneeded equipment. When I see something like this it generally
means that someone is having problems making the measurement and not
understanding the problems they are having. It could be they are having
reflections from the DUT screwing up the measurements and the amplifiers
and attenuators is their way of dealing with it. I could keep making
pointless speculations about this but you must see the point by now.

The need of attenuators and power divider on the generator outputs is
well understood. The generator outputs must have some degree of
isolation from each other so the test setup itself does not generate the
intermodulation products to be measured. I've made these measurements on
unity gain amplifiers with just two generators, two attenuators, a power
combiner and a spectrum analyzer. That's all you need.

Also troubling to me that they state the IP3 measurement can only
be made at some input power level and that it you will get a
different result at a different input power level. Well, you will
get the same result at different power levels as long as you
account for it and conditions #2, and #3 above so I don't
understand their problem with that.

As long as you are within the linear range of the DUT, this is true.

Yes, that is one of the conditions I stated and is a direct logical
requirement of this type of measurement.

They are also using filters. Using filters is OK as long as you
don't violate condition #1 above.

If you are using low-pass or bandpass filters at the output of each
generator and make sure that the tones are at the required level,
this is a non-issue.

Well OK for you to say that but I'm not so sure other people that make
measurements on SW radios and publish the results have paid proper
attention to this.

Sometimes, you might only have a filter that has a corner frequency
very close to your highest frequency of interest. Part of calibrating
the test setup is making sure that you have the correct power level
at every frequency that you are making the test at. What I would do
is measure the power level of the RF generators and LO generator at
every frequency of interest, and either use a correction factor for
setting the generator output manually, or I would enter the
correction factor into the Labview program when applicable. Since we
are making sure that the power levels are correct at all frequencies,
condition #1 is being met.

Very conscientious of you to follow proper procedure in calibrating out
the affects of support circuitry. It is the right approach but again for
the sake of discussion I can't know what it is you or Mini-circuits may
or may not be doing unless it is explicitly stated.

On a final note, I haven't done any multitone testing of
amplifiers..........my tests were limited to harmonic distortion,
noise figure, S-Parameters, and 1dB compression point. As I have
mentioned in the past, it sounds like you have been in the industry,
and I appreciate your input. One thing I didn't mention was a piece
of test equipment that makes these tests a little bit easier. Instead
of using a swept spectrum analyzer, a Vector Signal Analyzer (VSA) is
used. This instrument has a very wide dynamic range, with a noise
floor of -140dBm, even in a very wide passband. Since this is really
an FFT analyzer vs a swept analyzer, you aren't limited by very long
sweep times of the swept analyzer. Another new tool that has become
available from Agilent is the PSA. This is a spectrum analyzer with
added functions, but the best thing about this analyzer is the very
low sideband noise from its internal LO. This makes it possible to
look at the phase noise sidebands from an 8657 for instance, even at
1MHz away from the carrier. There were several different generators
from Agilent, Rohde and Schwarz, and Fluke, but the quietest units
they had around were still the 8642B. When I characterized one of
those unit at a 100kHz offset, I measured the noise down at -154dBc.
The new R&S stuff isn't bad, but the 8642 generators are still "king
of the hill".

I have some experience making these measurements. One thing about being
in electronics is change. I'm sure you know the drill. I have
experience in many areas out of necessity. Digital, analog, RF, mixed
signal, electromechanical, military, computers and so on.

Agilent make some good equipment. Always always have since they were
HP. The company where I work now has an Agilent PSA. The thing is still
slow on the noise measurements and I can't see how that type of
measurement could be speeded up while maintaining accuracy. I checked
the formula I posted against the IP2 and IP3 measurements it calculated
on some wide band amplifiers and they matched so I have some confidence
in them AND I ran the generators at different output levels and got the
same IP2 and IP3 numbers so it can be done with consistency at
different levels so there you have it Mini-circuits personnel.

The Agilent PSA is an OK piece of equipment that automates some
measurements.

Anritsu bought Wiltron a US manufacture of RF signal generators with
very good phase noise. The R&S claim to fame I saw as important at the
the time I was buying them was phase locking ability. Most RF generators
have frequency lock but the R&S generators have phase lock. Most people
(very smart people by the way) didn't understand the difference and
would fail BER measurements due to the multiple generators in the test
setup being frequency locked that occasionally slipped a cycle on a
telecommunications link. What is a few bits lost every few minutes
between friends anyway? Oh well, details, details...

--
Telamon
Ventura, California

Maybe that is what you were talking about but I'm trying to stay more
general. The formula and explanation I provided can be applied to RF
circuits in general not just mixers. Mixers comprise just one to three
stages in a radio generally. The rest of the circuits are filters and
amplifiers and detectors. With the right generalized approach you can
analyze any linear circuit or the whole radio.

When a receiver is being characterized for IP3, the 1st mixer is what is
being characterized in every case.


Well, its easy if you know all the specifications of the amplifiers or
have made the measurements on the test setup by itself. This is
something I can't do and would be making an assumption about.

This is something that is generally done in the industry today. It is more
or less the testing standard.

I don't understand why the amplifiers are need in the first place. Maybe
their generators have weak outputs.

Most RF generators today have an output of at least +15 to +20dBm, so
generator output is not an issue. The main reason for selecting these
amplifiers is twofold. First of all, they have very high reverse isolation,
and second, they have very low harmonic distortion and very good multitone
response.

The test setup is overly complex and has unneeded equipment. When I see
something like this it generally
means that someone is having problems making the measurement and not
understanding the problems they are having.

From the above statement, I have to deduce that you haven't really made too
many mixer characterizations. If you had, you would have discovered that a
"complex" setup is necessary when characterizing low distortion mixers.
If you are measuring the IP3 of the newer RF switches and digital step
attenuators, this "complex" setup just barely makes the grade.

It could be they are having
reflections from the DUT screwing up the measurements and the amplifiers
and attenuators is their way of dealing with it. I could keep making
pointless speculations about this but you must see the point by now.

No, I don't see your point.

The need of attenuators and power divider on the generator outputs is
well understood. The generator outputs must have some degree of
isolation from each other so the test setup itself does not generate the
intermodulation products to be measured. I've made these measurements on
unity gain amplifiers with just two generators, two attenuators, a power
combiner and a spectrum analyzer. That's all you need.

Perhaps this setup is adequate for unity gain amplifiers, but it doesn't
even come close if you have to characterize high performance mixers. You
might thing the setup is working well, but you would discover very quickly
that one of the newer mixers isn't meeting its specifications.
understand their problem with that.
above.

If you are using low-pass or bandpass filters at the output of each
generator and make sure that the tones are at the required level,
this is a non-issue.

Well OK for you to say that but I'm not so sure other people that make
measurements on SW radios and publish the results have paid proper
attention to this.

I am not sure about that.......if they are not following these guidelines
and if different reviewers are using different topologies with their test
setups, there is no standard to compare by.
A similar problem occurs with microscope specifications. As an example, with
planachromatic objectives one manufacturer might specify a plan objective as
having a flat field with good color correction over at least 90% of the
viewing field while another manufacturer would use 85% as a specification.

Here is another problem when making IP3 measurements, or any distortion
measurement...........when you are looking at distortion components that are
at -100dBc or lower, even connectors can contribute to the measured result.
When selecting attenuators, the ones with the transverse heatsink fins do
have lower IMD properties, so these are the ones to use.

Sometimes, you might only have a filter that has a corner frequency
very close to your highest frequency of interest. Part of calibrating
the test setup is making sure that you have the correct power level
at every frequency that you are making the test at. What I would do
is measure the power level of the RF generators and LO generator at
every frequency of interest, and either use a correction factor for
setting the generator output manually, or I would enter the
correction factor into the Labview program when applicable. Since we
are making sure that the power levels are correct at all frequencies,
condition #1 is being met.

Very conscientious of you to follow proper procedure in calibrating out
the affects of support circuitry. It is the right approach but again for
the sake of discussion I can't know what it is you or Mini-circuits may
or may not be doing unless it is explicitly stated.

That is why I provided the PDF link from Mini-Circuits..............they are
pretty succint in the appnote.

On a final note, I haven't done any multitone testing of
amplifiers..........my tests were limited to harmonic distortion,
noise figure, S-Parameters, and 1dB compression point. As I have
mentioned in the past, it sounds like you have been in the industry,
and I appreciate your input. One thing I didn't mention was a piece
of test equipment that makes these tests a little bit easier. Instead
of using a swept spectrum analyzer, a Vector Signal Analyzer (VSA) is
used. This instrument has a very wide dynamic range, with a noise
floor of -140dBm, even in a very wide passband. Since this is really
an FFT analyzer vs a swept analyzer, you aren't limited by very long
sweep times of the swept analyzer. Another new tool that has become
available from Agilent is the PSA. This is a spectrum analyzer with
added functions, but the best thing about this analyzer is the very
low sideband noise from its internal LO. This makes it possible to
look at the phase noise sidebands from an 8657 for instance, even at
1MHz away from the carrier. There were several different generators
from Agilent, Rohde and Schwarz, and Fluke, but the quietest units
they had around were still the 8642B. When I characterized one of
those unit at a 100kHz offset, I measured the noise down at -154dBc.
The new R&S stuff isn't bad, but the 8642 generators are still "king
of the hill".

I have some experience making these measurements. One thing about being
in electronics is change. I'm sure you know the drill. I have
experience in many areas out of necessity. Digital, analog, RF, mixed
signal, electromechanical, military, computers and so on.

I have no doubt about your ability.......it appears that you have quite a
bit of experience in this field.

Agilent make some good equipment. Always always have since they were
HP. The company where I work now has an Agilent PSA. The thing is still
slow on the noise measurements and I can't see how that type of
measurement could be speeded up while maintaining accuracy. I checked
the formula I posted against the IP2 and IP3 measurements it calculated
on some wide band amplifiers and they matched so I have some confidence
in them AND I ran the generators at different output levels and got the
same IP2 and IP3 numbers so it can be done with consistency at
different levels so there you have it Mini-circuits personnel.

I have noted the same thing, as long as I was working within the linear
range of the DUT. As far as noise testing, I think you are talking about
phase noise. If that is the case, Agilent has a new phase noise/VCO test
system that can measure down to below -160dBc. We were using it with some of
the new VCOs (in-house design). Still, when measuring down at that level,
external factors can affect the measurement. When were were testing the VCOs
at -40C, there were some spikes in the phase noise spectrum.
The firing of the SCRs in the environmental chamber were causing
perturbation of the tuning voltage from radiated emissions. These were very
low frequency harmonics of 60hZ...............the 3rd and 4th harmonic were
causing the problems.

The Agilent PSA is an OK piece of equipment that automates some
measurements.

Anritsu bought Wiltron a US manufacture of RF signal generators with
very good phase noise. The R&S claim to fame I saw as important at the
the time I was buying them was phase locking ability. Most RF generators
have frequency lock but the R&S generators have phase lock. Most people
(very smart people by the way) didn't understand the difference and
would fail BER measurements due to the multiple generators in the test
setup being frequency locked that occasionally slipped a cycle on a
telecommunications link. What is a few bits lost every few minutes
between friends anyway? Oh well, details, details...

I remember when I was working at Rockwell-Collins. They had buffered 10MHz
signals running through all of the labs that we used to connect all of the
generators and spectrum analyzers to. This was also important when
characterizing the frequency hop synthesizers.
Same thing at Motorola.......we used to sync all of the equipment when we
were measuring BER of some of the newer radios.
Those R&S generators were pretty good. When we were looking at new
generators years back, we had samples of the Agilent E series and of the R&S
SMY-01s. Those SMY-01s were pretty nice, but not as clean as the 8642s.
We used them as the reference oscillator with new synthesizer designs. At
wide frequency offsets, the phase noise of the synthesizers were about the
same with both generators, but at a 7kHz offset there was a 25dB disparity
between the two, with the 8642 coming out better.
Another thing about the SMY-01s...............many of them had failures in
the phase lock loop section.
I haven't seen this problem with the newer R&S units..........they have been
very reliable. Wouldn't be bad for a home unit!
I remember the 8640s used frequency locking, and if you connected the
generator to a high resolution frequency counter you would see the output
frequency warp up and down by a few Hz over a period of time.
That is the reason that I still have my old Boonton 103D. This generator has
phase noise in the -143dBc range and it has a dedicated OCXO for the phase
locking function.

Oh well...........time to get ready for work again.............nice talking
(bantering?) with you. I don't mind intelligent debates!

Pete

In article ,
"Pete KE9OA" wrote:

Maybe that is what you were talking about but I'm trying to stay
more general. The formula and explanation I provided can be applied
to RF circuits in general not just mixers. Mixers comprise just one
to three stages in a radio generally. The rest of the circuits are
filters and amplifiers and detectors. With the right generalized
approach you can analyze any linear circuit or the whole radio.

When a receiver is being characterized for IP3, the 1st mixer is what
is being characterized in every case.

What? All the rest of the radio circuitry has nothing to do with IP3?

Well, its easy if you know all the specifications of the amplifiers
or have made the measurements on the test setup by itself. This is
something I can't do and would be making an assumption about.

This is something that is generally done in the industry today. It is
more or less the testing standard.

Then explain why this is a industry standard way of making these
measurements.

I don't understand why the amplifiers are need in the first place.
Maybe their generators have weak outputs.

Most RF generators today have an output of at least +15 to +20dBm, so
generator output is not an issue. The main reason for selecting these
amplifiers is twofold. First of all, they have very high reverse
isolation, and second, they have very low harmonic distortion and
very good multitone response.

Makes no sense to me. Why would a separate amplifier not have the same
problem as the output amplifier in the generator? The attenuators on
the generator outputs before the power combiner and the power combiner
itself (resistive type) are are supposed to provide the isolation of
the generator outputs.

Why is some additional amount of reverse isolation the amplifier
provides needed?

The test setup is overly complex and has unneeded equipment. When I
see something like this it generally
means that someone is having problems making the measurement and
not understanding the problems they are having.

From the above statement, I have to deduce that you haven't really
made too many mixer characterizations. If you had, you would have
discovered that a "complex" setup is necessary when characterizing
low distortion mixers. If you are measuring the IP3 of the newer RF
switches and digital step attenuators, this "complex" setup just
barely makes the grade.

Yeah, I have not made any measurements on a mixer.

You mean solid state switches and step attenuators? Why are additional
amplifiers, attenuators, and filters needed for those?

It could be they are having reflections from the DUT screwing up
the measurements and the amplifiers and attenuators is their way of
dealing with it. I could keep making pointless speculations about
this but you must see the point by now.

No, I don't see your point.

Pretty simple point, it is my observation of RF test setups measuring
this, that, or the other people have created when having problems
making a measurement over many years time. It's not an inditement it
just raises my suspicions.

There has to be a reason that you use an amplifier to boost a signal
followed by attenuators to cut it back down. There has to be a reason
you think you need some additional amount of reverse isolation in the
fixture.

My guess is that the DUT input and output impedance is not a flat 50
ohms over the measurement range and the reflections play havoc with the
measurements. If that is the case then fix the DUT design not add junk
to the fixturing that needs to be calibrated out of the DUT
measurements.

The need of attenuators and power divider on the generator outputs
is well understood. The generator outputs must have some degree of
isolation from each other so the test setup itself does not
generate the intermodulation products to be measured. I've made
these measurements on unity gain amplifiers with just two
generators, two attenuators, a power combiner and a spectrum
analyzer. That's all you need.

Perhaps this setup is adequate for unity gain amplifiers, but it
doesn't even come close if you have to characterize high performance
mixers. You might thing the setup is working well, but you would
discover very quickly that one of the newer mixers isn't meeting its
specifications. understand their problem with that. above.

The unity gain amplifier was just an example that I used because their
is no gain and it might be a reason amplification is needed somewhere
in the fixturing with the attenuation needed for isolation of the
generator outputs.

If you are using low-pass or bandpass filters at the output of
each generator and make sure that the tones are at the required
level, this is a non-issue.

Well OK for you to say that but I'm not so sure other people that
make measurements on SW radios and publish the results have paid
proper attention to this.

I am not sure about that.......if they are not following these
guidelines and if different reviewers are using different topologies
with their test setups, there is no standard to compare by.

Bingo.

A similar problem occurs with microscope specifications. As an
example, with planachromatic objectives one manufacturer might
specify a plan objective as having a flat field with good color
correction over at least 90% of the viewing field while another
manufacturer would use 85% as a specification.

Gotcha.

Here is another problem when making IP3 measurements, or any
distortion measurement...........when you are looking at distortion
components that are at -100dBc or lower, even connectors can
contribute to the measured result. When selecting attenuators, the
ones with the transverse heatsink fins do have lower IMD properties,
so these are the ones to use.

My work is mostly small signal so attenuators I use don't have fins but
ya got me why transverse cooling fins would make an IMD difference.

Sometimes, you might only have a filter that has a corner
frequency very close to your highest frequency of interest. Part
of calibrating the test setup is making sure that you have the
correct power level at every frequency that you are making the
test at. What I would do is measure the power level of the RF
generators and LO generator at every frequency of interest, and
either use a correction factor for setting the generator output
manually, or I would enter the correction factor into the Labview
program when applicable. Since we are making sure that the power
levels are correct at all frequencies, condition #1 is being met.

Very conscientious of you to follow proper procedure in calibrating
out the affects of support circuitry. It is the right approach but
again for the sake of discussion I can't know what it is you or
Mini-circuits may or may not be doing unless it is explicitly
stated.

That is why I provided the PDF link from
Mini-Circuits..............they are pretty succint in the appnote.

I pretty much did not like what I read there. Good company, good
products but that pdf left me desiring more explanation of some of
their conclusions.

On a final note, I haven't done any multitone testing of
amplifiers..........my tests were limited to harmonic distortion,
noise figure, S-Parameters, and 1dB compression point. As I have
mentioned in the past, it sounds like you have been in the
industry, and I appreciate your input. One thing I didn't mention
was a piece of test equipment that makes these tests a little bit
easier. Instead of using a swept spectrum analyzer, a Vector
Signal Analyzer (VSA) is used. This instrument has a very wide
dynamic range, with a noise floor of -140dBm, even in a very wide
passband. Since this is really an FFT analyzer vs a swept
analyzer, you aren't limited by very long sweep times of the swept
analyzer. Another new tool that has become available from Agilent
is the PSA. This is a spectrum analyzer with added functions, but
the best thing about this analyzer is the very low sideband noise
from its internal LO. This makes it possible to look at the phase
noise sidebands from an 8657 for instance, even at 1MHz away from
the carrier. There were several different generators from Agilent,
Rohde and Schwarz, and Fluke, but the quietest units they had
around were still the 8642B. When I characterized one of those
unit at a 100kHz offset, I measured the noise down at -154dBc. The
new R&S stuff isn't bad, but the 8642 generators are still "king
of the hill".

I have some experience making these measurements. One thing about
being in electronics is change. I'm sure you know the drill. I have
experience in many areas out of necessity. Digital, analog, RF,
mixed signal, electromechanical, military, computers and so on.

I have no doubt about your ability.......it appears that you have
quite a bit of experience in this field.

Agilent make some good equipment. Always always have since they
were HP. The company where I work now has an Agilent PSA. The thing
is still slow on the noise measurements and I can't see how that
type of measurement could be speeded up while maintaining accuracy.
I checked the formula I posted against the IP2 and IP3 measurements
it calculated on some wide band amplifiers and they matched so I
have some confidence in them AND I ran the generators at different
output levels and got the same IP2 and IP3 numbers so it can be
done with consistency at different levels so there you have it
Mini-circuits personnel.

I have noted the same thing, as long as I was working within the
linear range of the DUT. As far as noise testing, I think you are
talking about phase noise. If that is the case, Agilent has a new
phase noise/VCO test system that can measure down to below -160dBc.
We were using it with some of the new VCOs (in-house design). Still,
when measuring down at that level, external factors can affect the
measurement. When were were testing the VCOs at -40C, there were some
spikes in the phase noise spectrum. The firing of the SCRs in the
environmental chamber were causing perturbation of the tuning voltage
from radiated emissions. These were very low frequency harmonics of
60hZ...............the 3rd and 4th harmonic were causing the
problems.

Yeah, chambers of any type and vibration tables always add another
dimension of "fun" when the DUT is not making specifications and don't
you just love it when the problem turns out to be test equipment
instead of the DUT.

The Agilent PSA is an OK piece of equipment that automates some
measurements.

Anritsu bought Wiltron a US manufacture of RF signal generators
with very good phase noise. The R&S claim to fame I saw as
important at the the time I was buying them was phase locking
ability. Most RF generators have frequency lock but the R&S
generators have phase lock. Most people (very smart people by the
way) didn't understand the difference and would fail BER
measurements due to the multiple generators in the test setup being
frequency locked that occasionally slipped a cycle on a
telecommunications link. What is a few bits lost every few minutes
between friends anyway? Oh well, details, details...

I remember when I was working at Rockwell-Collins. They had buffered
10MHz signals running through all of the labs that we used to connect
all of the generators and spectrum analyzers to. This was also
important when characterizing the frequency hop synthesizers. Same
thing at Motorola.......we used to sync all of the equipment when we
were measuring BER of some of the newer radios. Those R&S generators
were pretty good. When we were looking at new generators years back,
we had samples of the Agilent E series and of the R&S SMY-01s. Those
SMY-01s were pretty nice, but not as clean as the 8642s. We used them
as the reference oscillator with new synthesizer designs. At wide
frequency offsets, the phase noise of the synthesizers were about the
same with both generators, but at a 7kHz offset there was a 25dB
disparity between the two, with the 8642 coming out better. Another
thing about the SMY-01s...............many of them had failures in
the phase lock loop section. I haven't seen this problem with the
newer R&S units..........they have been very reliable. Wouldn't be
bad for a home unit! I remember the 8640s used frequency locking, and
if you connected the generator to a high resolution frequency counter
you would see the output frequency warp up and down by a few Hz ov er
a period of time. That is the reason that I still have my old Boonton
103D. This generator has phase noise in the -143dBc range and it has
a dedicated OCXO for the phase locking function.

Oh well...........time to get ready for work again.............nice
talking (bantering?) with you. I don't mind intelligent debates!

I don't care for debates, I'm interested in learning. You are right
that I've never characterized a mixer so maybe you can explain the
reason for the filters, attenuators and amplifiers in the test setup. I
explained why I thought them unnecessary and I do not understand why
they are necessary as a standard way of characterizing a mixer. Sure
you can connect everything together without the DUT and characterize
the fixturing. These measurements can either be a floor you can't
measure below or ceiling you can't measure above on the DUT or used as
a fixture compensation on the DUT measurement depending on the
measurement type but generally fixture compensation is to be avoided
unless necessary. It is a much better situation that the fixturing be
transparent to the measurements.

--
Telamon
Ventura, California