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