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XG3 device...

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John Ragle

XG3 device...

The more I have glanced through the specs for this device, the more
puzzled I have become. I grew up on signal generators that put out a
(good approximation to a) sine wave. This device is described as an RF
"square wave" generator, which I take to mean that the output wave shape
is a trapezoid with very fast rise and fall times. As everyone knows,
the harmonic content of an ideal square wave falls off as 1/N. In other
words, this device is a harmonic generator, par excellence, very rich in
harmonic content. To get a sine wave, one has to run it through a
bandpass filter. In this case, the bandpass filter is the receiver to
which you connect it.

So there are two questions.

1. What is the "frequency?" This term usually refers to a sinusoid, in
which case the answer is trivial. Presumably the "frequency" meant here
is the fundamental component of the "square" wave, but the true answer
depends on the shape of the on/off switching, which presumably depends
on the "frequency" one has dialed into the device. Is one getting more
or less a 1/N dependence on amplitude at all frequencies?

2. When one refers to the calibrated "levels" of output, is one
referring to the level of the square wave or of its fundamental
sinusoidal component? Clearly, these are related...but which is meant?
What about the high frequency end of the operating range, where the
spectrum may well depart substantially from 1/N (because the trapezoid's
edges are less "sharp").

Neither of these questions has anything to do with the "phase noise"
specification.

John Ragle -- W1ZI
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n7ws

Re: XG3 device...

Good questions. I had them myself, especially #2.

Wes

--- On Thu, 4/14/11, John Ragle <[hidden email]> wrote:

> The more I
> have glanced through the specs for this device, the more
> puzzled I have become. I grew up on signal generators that
> put out a
> (good approximation to a) sine wave. This device is
> described as an RF
> "square wave" generator, which I take to mean that the
> output wave shape
> is a trapezoid with very fast rise and fall times. As
> everyone knows,
> the harmonic content of an ideal square wave falls off as
> 1/N. In other
> words, this device is a harmonic generator, par excellence,
> very rich in
> harmonic content. To get a sine wave, one has to run it
> through a
> bandpass filter. In this case, the bandpass filter is the
> receiver to
> which you connect it.
>
> So there are two questions.
>
> 1. What is the "frequency?" This term usually refers to a
> sinusoid, in
> which case the answer is trivial. Presumably the
> "frequency" meant here
> is the fundamental component of the "square" wave, but the
> true answer
> depends on the shape of the on/off switching, which
> presumably depends
> on the "frequency" one has dialed into the device. Is one
> getting more
> or less a 1/N dependence on amplitude at all frequencies?
>
> 2. When one refers to the calibrated "levels" of output, is
> one
> referring to the level of the square wave or of its
> fundamental
> sinusoidal component? Clearly, these are related...but
> which is meant?
> What about the high frequency end of the operating range,
> where the
> spectrum may well depart substantially from 1/N (because
> the trapezoid's
> edges are less "sharp").
>
> Neither of these questions has anything to do with the
> "phase noise"
> specification.
>
> John Ragle -- W1ZI
> ______________________________

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AC7AC

Re: XG3 device...

In reply to this post by John Ragle

CONTENTS DELETED

The author has deleted this message.

Tony Estep

Re: XG3 device...

On Thu, Apr 14, 2011 at 10:32 AM, Ron D'Eau Claire <[hidden email]> wrote:

> A square wave's frequency....
>
>
>
Ron, I think John is aksing about the calibrated power (John, correct me
if I'm mis-stating here). If there are infinite harmonics each
with amplitude = 1/N, then 1/2 of the total energy will be at the
fundamental freqency, and 1/2 will be in the sum of all the higher
harmonics. So if you say that the output is, say, 1 mW and the frequency is
1 MHz, does that mean that there is 1mW of output at 1 MHz and another 1 mW
of output in the harmonics? or what?

Tony KT0NY
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Robert Friess

Re: XG3 device...

All XG3 amplitude references refer to the amplitude of the fundamental
frequency component only.

Bob, N6CM

On Thu, Apr 14, 2011 at 9:09 AM, Tony Estep <[hidden email]> wrote:

> On Thu, Apr 14, 2011 at 10:32 AM, Ron D'Eau Claire <[hidden email]> wrote:
>
> > A square wave's frequency....
> >
> >
> >
> Ron, I think John is aksing about the calibrated power (John, correct me
> if I'm mis-stating here). If there are infinite harmonics each
> with amplitude = 1/N, then 1/2 of the total energy will be at the
> fundamental freqency, and 1/2 will be in the sum of all the higher
> harmonics. So if you say that the output is, say, 1 mW and the frequency
> is
> 1 MHz, does that mean that there is 1mW of output at 1 MHz and another 1 mW
> of output in the harmonics? or what?
>
> Tony KT0NY
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Alan Bloom

Re: XG3 device...

In reply to this post by John Ragle

Question 1: The frequency is based on the period of the square wave, in
other words, the frequency of the fundamental. If you program a
frequency greater than the maximum 200 MHz, software automatically
selects the proper fundamental so that the harmonic comes out at the
desired frequency.

Question 2: I wasn't one of the XG3 designers, but my understanding is
that the amplitude is that of the fundamental (the sine-wave portion)
and does not include the harmonics. When you are operating on a
harmonic, the amplitude is uncalibrated. Although theoretically the
third harmonic is 1/3 the amplitude (-9.5 dB) and the fifth is 1/5 the
amplitude (-14 dB) it is not very accurate because of the finite
rise/fall times of the square wave.

For most things you use a signal generator for, the harmonics don't hurt
anything - they are filtered out by the receiver or other device under
test. Even expensive professional signal generators typically only
specify 30 or 40 dB harmonic suppression.

Alan N1AL

On Thu, 2011-04-14 at 04:14 -0400, John Ragle wrote:

> The more I have glanced through the specs for this device, the more
> puzzled I have become. I grew up on signal generators that put out a
> (good approximation to a) sine wave. This device is described as an RF
> "square wave" generator, which I take to mean that the output wave shape
> is a trapezoid with very fast rise and fall times. As everyone knows,
> the harmonic content of an ideal square wave falls off as 1/N. In other
> words, this device is a harmonic generator, par excellence, very rich in
> harmonic content. To get a sine wave, one has to run it through a
> bandpass filter. In this case, the bandpass filter is the receiver to
> which you connect it.
>
> So there are two questions.
>
> 1. What is the "frequency?" This term usually refers to a sinusoid, in
> which case the answer is trivial. Presumably the "frequency" meant here
> is the fundamental component of the "square" wave, but the true answer
> depends on the shape of the on/off switching, which presumably depends
> on the "frequency" one has dialed into the device. Is one getting more
> or less a 1/N dependence on amplitude at all frequencies?
>
> 2. When one refers to the calibrated "levels" of output, is one
> referring to the level of the square wave or of its fundamental
> sinusoidal component? Clearly, these are related...but which is meant?
> What about the high frequency end of the operating range, where the
> spectrum may well depart substantially from 1/N (because the trapezoid's
> edges are less "sharp").
>
> Neither of these questions has anything to do with the "phase noise"
> specification.
>
> John Ragle -- W1ZI
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Scott Ellington

Re: XG3 device...

It's implicit in Alan's posting, but note that symmetrical square waves have only odd harmonics. The even harmonics will be very, very weak, present at all only because the square wave isn't quite perfectly symmetric.

Scott K9MA

Scott Ellington
Madison, Wisconsin
USA

On Apr 14, 2011, at 1:26 PM, Alan Bloom wrote:

Jack Smith-6

Re: XG3 device...

In reply to this post by Alan Bloom

Alan:

One are where a square wave RF source can get you into trouble is 2nd
and 3rd order intermodulation measurements.

Mini-Circuits Ap Note 00008 discusses the reason why.
http://www.minicircuits.com/pages/pdfs/AN00008.pdf

I usually use an outboard low pass filter on my HP 8657A signal
generators when making IMD measurements of high performance amplifiers,
and it's not a bad idea even with HP 8640B generators which are 60 dB+
down on the harmonics.

As far as a low pass filter goes, CoilCraft has some very inexpensive
($3 range) 7th order elliptical low pass filter modules, the P7LP
series, with cutoff frequencies from 300 KHz to 500 MHz.
http://www.coilcraft.com/pdfs/lcfilt.pdf These are perfectly fine for
output filtering of a single generator, but should not be used with
multiple signals as they can themselves be intermod generators. I use
them here for various tasks including signal generator clean up.

If anyone is interested, I have a few extra printed circuit boards with
provisions for PCB-mount BNC connectors and a P7LP filter and can make
them available at a reasonable price (PCB only, you supply the
connectors and filter modules). Usual double sided, silk screen, solder
masked boards. I have installed a socket strip in one as an experiment
so that one might just plug in the appropriate filter, but that's not a
great idea as the filter modules are not all that mechanically robust
and the extra lead inductance from the socket degrades stop band
performance at higher frequencies. I can send a photo of the board to
anyone interested.

Jack K8ZOA

On 4/14/2011 2:26 PM, Alan Bloom wrote:

> Question 1: The frequency is based on the period of the square wave, in
> other words, the frequency of the fundamental. If you program a
> frequency greater than the maximum 200 MHz, software automatically
> selects the proper fundamental so that the harmonic comes out at the
> desired frequency.
>
> Question 2: I wasn't one of the XG3 designers, but my understanding is
> that the amplitude is that of the fundamental (the sine-wave portion)
> and does not include the harmonics. When you are operating on a
> harmonic, the amplitude is uncalibrated. Although theoretically the
> third harmonic is 1/3 the amplitude (-9.5 dB) and the fifth is 1/5 the
> amplitude (-14 dB) it is not very accurate because of the finite
> rise/fall times of the square wave.
>
> For most things you use a signal generator for, the harmonics don't hurt
> anything - they are filtered out by the receiver or other device under
> test. Even expensive professional signal generators typically only
> specify 30 or 40 dB harmonic suppression.
>
> Alan N1AL
>
>
> On Thu, 2011-04-14 at 04:14 -0400, John Ragle wrote:
>> The more I have glanced through the specs for this device, the more
>> puzzled I have become. I grew up on signal generators that put out a
>> (good approximation to a) sine wave. This device is described as an RF
>> "square wave" generator, which I take to mean that the output wave shape
>> is a trapezoid with very fast rise and fall times. As everyone knows,
>> the harmonic content of an ideal square wave falls off as 1/N. In other
>> words, this device is a harmonic generator, par excellence, very rich in
>> harmonic content. To get a sine wave, one has to run it through a
>> bandpass filter. In this case, the bandpass filter is the receiver to
>> which you connect it.
>>
>> So there are two questions.
>>
>> 1. What is the "frequency?" This term usually refers to a sinusoid, in
>> which case the answer is trivial. Presumably the "frequency" meant here
>> is the fundamental component of the "square" wave, but the true answer
>> depends on the shape of the on/off switching, which presumably depends
>> on the "frequency" one has dialed into the device. Is one getting more
>> or less a 1/N dependence on amplitude at all frequencies?
>>
>> 2. When one refers to the calibrated "levels" of output, is one
>> referring to the level of the square wave or of its fundamental
>> sinusoidal component? Clearly, these are related...but which is meant?
>> What about the high frequency end of the operating range, where the
>> spectrum may well depart substantially from 1/N (because the trapezoid's
>> edges are less "sharp").
>>
>> Neither of these questions has anything to do with the "phase noise"
>> specification.
>>
>> John Ragle -- W1ZI
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Alan Bloom

Re: XG3 device...

Hi Jack,

You're right that when testing a wide-band device like an amplifier you
have to filter out the generator harmonics in order to get a valid
third-order IMD test. But when testing a narrow-band device like a
receiver the harmonics are normally not an issue.

Those Coilcraft low-pass filters look very nice, especially for he
price. Where can you buy them?

Alan N1AL

On Thu, 2011-04-14 at 16:54 -0400, Jack Smith wrote:

> Alan:
>
> One are where a square wave RF source can get you into trouble is 2nd
> and 3rd order intermodulation measurements.
>
> Mini-Circuits Ap Note 00008 discusses the reason why.
> http://www.minicircuits.com/pages/pdfs/AN00008.pdf
>
> I usually use an outboard low pass filter on my HP 8657A signal
> generators when making IMD measurements of high performance amplifiers,
> and it's not a bad idea even with HP 8640B generators which are 60 dB+
> down on the harmonics.
>
> As far as a low pass filter goes, CoilCraft has some very inexpensive
> ($3 range) 7th order elliptical low pass filter modules, the P7LP
> series, with cutoff frequencies from 300 KHz to 500 MHz.
> http://www.coilcraft.com/pdfs/lcfilt.pdf These are perfectly fine for
> output filtering of a single generator, but should not be used with
> multiple signals as they can themselves be intermod generators. I use
> them here for various tasks including signal generator clean up.
>
> If anyone is interested, I have a few extra printed circuit boards with
> provisions for PCB-mount BNC connectors and a P7LP filter and can make
> them available at a reasonable price (PCB only, you supply the
> connectors and filter modules). Usual double sided, silk screen, solder
> masked boards. I have installed a socket strip in one as an experiment
> so that one might just plug in the appropriate filter, but that's not a
> great idea as the filter modules are not all that mechanically robust
> and the extra lead inductance from the socket degrades stop band
> performance at higher frequencies. I can send a photo of the board to
> anyone interested.
>
> Jack K8ZOA
>
>
>
>
>
>
> On 4/14/2011 2:26 PM, Alan Bloom wrote:
> > Question 1: The frequency is based on the period of the square wave, in
> > other words, the frequency of the fundamental. If you program a
> > frequency greater than the maximum 200 MHz, software automatically
> > selects the proper fundamental so that the harmonic comes out at the
> > desired frequency.
> >
> > Question 2: I wasn't one of the XG3 designers, but my understanding is
> > that the amplitude is that of the fundamental (the sine-wave portion)
> > and does not include the harmonics. When you are operating on a
> > harmonic, the amplitude is uncalibrated. Although theoretically the
> > third harmonic is 1/3 the amplitude (-9.5 dB) and the fifth is 1/5 the
> > amplitude (-14 dB) it is not very accurate because of the finite
> > rise/fall times of the square wave.
> >
> > For most things you use a signal generator for, the harmonics don't hurt
> > anything - they are filtered out by the receiver or other device under
> > test. Even expensive professional signal generators typically only
> > specify 30 or 40 dB harmonic suppression.
> >
> > Alan N1AL
> >
> >
> > On Thu, 2011-04-14 at 04:14 -0400, John Ragle wrote:
> >> The more I have glanced through the specs for this device, the more
> >> puzzled I have become. I grew up on signal generators that put out a
> >> (good approximation to a) sine wave. This device is described as an RF
> >> "square wave" generator, which I take to mean that the output wave shape
> >> is a trapezoid with very fast rise and fall times. As everyone knows,
> >> the harmonic content of an ideal square wave falls off as 1/N. In other
> >> words, this device is a harmonic generator, par excellence, very rich in
> >> harmonic content. To get a sine wave, one has to run it through a
> >> bandpass filter. In this case, the bandpass filter is the receiver to
> >> which you connect it.
> >>
> >> So there are two questions.
> >>
> >> 1. What is the "frequency?" This term usually refers to a sinusoid, in
> >> which case the answer is trivial. Presumably the "frequency" meant here
> >> is the fundamental component of the "square" wave, but the true answer
> >> depends on the shape of the on/off switching, which presumably depends
> >> on the "frequency" one has dialed into the device. Is one getting more
> >> or less a 1/N dependence on amplitude at all frequencies?
> >>
> >> 2. When one refers to the calibrated "levels" of output, is one
> >> referring to the level of the square wave or of its fundamental
> >> sinusoidal component? Clearly, these are related...but which is meant?
> >> What about the high frequency end of the operating range, where the
> >> spectrum may well depart substantially from 1/N (because the trapezoid's
> >> edges are less "sharp").
> >>
> >> Neither of these questions has anything to do with the "phase noise"
> >> specification.
> >>
> >> John Ragle -- W1ZI
> >> ______________________________________________________________
> >> Elecraft mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:[hidden email]
> >>
> >> This list hosted by: http://www.qsl.net
> >> Please help support this email list: http://www.qsl.net/donate.html
> >>
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Jack Smith-6

Re: XG3 device...

Alan:

Coilcraft is direct sales only - no minimum quantity for internet orders
and they are pretty good about free samples if you have a business name
and address.

Jack K8ZOA

On 4/14/2011 5:58 PM, Alan Bloom wrote:

> Hi Jack,
>
> You're right that when testing a wide-band device like an amplifier you
> have to filter out the generator harmonics in order to get a valid
> third-order IMD test. But when testing a narrow-band device like a
> receiver the harmonics are normally not an issue.
>
> Those Coilcraft low-pass filters look very nice, especially for he
> price. Where can you buy them?
>
> Alan N1AL
>
>
> On Thu, 2011-04-14 at 16:54 -0400, Jack Smith wrote:
>> Alan:
>>
>> One are where a square wave RF source can get you into trouble is 2nd
>> and 3rd order intermodulation measurements.
>>
>> Mini-Circuits Ap Note 00008 discusses the reason why.
>> http://www.minicircuits.com/pages/pdfs/AN00008.pdf
>>
>> I usually use an outboard low pass filter on my HP 8657A signal
>> generators when making IMD measurements of high performance amplifiers,
>> and it's not a bad idea even with HP 8640B generators which are 60 dB+
>> down on the harmonics.
>>
>> As far as a low pass filter goes, CoilCraft has some very inexpensive
>> ($3 range) 7th order elliptical low pass filter modules, the P7LP
>> series, with cutoff frequencies from 300 KHz to 500 MHz.
>> http://www.coilcraft.com/pdfs/lcfilt.pdf These are perfectly fine for
>> output filtering of a single generator, but should not be used with
>> multiple signals as they can themselves be intermod generators. I use
>> them here for various tasks including signal generator clean up.
>>
>> If anyone is interested, I have a few extra printed circuit boards with
>> provisions for PCB-mount BNC connectors and a P7LP filter and can make
>> them available at a reasonable price (PCB only, you supply the
>> connectors and filter modules). Usual double sided, silk screen, solder
>> masked boards. I have installed a socket strip in one as an experiment
>> so that one might just plug in the appropriate filter, but that's not a
>> great idea as the filter modules are not all that mechanically robust
>> and the extra lead inductance from the socket degrades stop band
>> performance at higher frequencies. I can send a photo of the board to
>> anyone interested.
>>
>> Jack K8ZOA
>>
>>
>>
>>
>>
>>
>> On 4/14/2011 2:26 PM, Alan Bloom wrote:
>>> Question 1: The frequency is based on the period of the square wave, in
>>> other words, the frequency of the fundamental. If you program a
>>> frequency greater than the maximum 200 MHz, software automatically
>>> selects the proper fundamental so that the harmonic comes out at the
>>> desired frequency.
>>>
>>> Question 2: I wasn't one of the XG3 designers, but my understanding is
>>> that the amplitude is that of the fundamental (the sine-wave portion)
>>> and does not include the harmonics. When you are operating on a
>>> harmonic, the amplitude is uncalibrated. Although theoretically the
>>> third harmonic is 1/3 the amplitude (-9.5 dB) and the fifth is 1/5 the
>>> amplitude (-14 dB) it is not very accurate because of the finite
>>> rise/fall times of the square wave.
>>>
>>> For most things you use a signal generator for, the harmonics don't hurt
>>> anything - they are filtered out by the receiver or other device under
>>> test. Even expensive professional signal generators typically only
>>> specify 30 or 40 dB harmonic suppression.
>>>
>>> Alan N1AL
>>>
>>>
>>> On Thu, 2011-04-14 at 04:14 -0400, John Ragle wrote:
>>>> The more I have glanced through the specs for this device, the more
>>>> puzzled I have become. I grew up on signal generators that put out a
>>>> (good approximation to a) sine wave. This device is described as an RF
>>>> "square wave" generator, which I take to mean that the output wave shape
>>>> is a trapezoid with very fast rise and fall times. As everyone knows,
>>>> the harmonic content of an ideal square wave falls off as 1/N. In other
>>>> words, this device is a harmonic generator, par excellence, very rich in
>>>> harmonic content. To get a sine wave, one has to run it through a
>>>> bandpass filter. In this case, the bandpass filter is the receiver to
>>>> which you connect it.
>>>>
>>>> So there are two questions.
>>>>
>>>> 1. What is the "frequency?" This term usually refers to a sinusoid, in
>>>> which case the answer is trivial. Presumably the "frequency" meant here
>>>> is the fundamental component of the "square" wave, but the true answer
>>>> depends on the shape of the on/off switching, which presumably depends
>>>> on the "frequency" one has dialed into the device. Is one getting more
>>>> or less a 1/N dependence on amplitude at all frequencies?
>>>>
>>>> 2. When one refers to the calibrated "levels" of output, is one
>>>> referring to the level of the square wave or of its fundamental
>>>> sinusoidal component? Clearly, these are related...but which is meant?
>>>> What about the high frequency end of the operating range, where the
>>>> spectrum may well depart substantially from 1/N (because the trapezoid's
>>>> edges are less "sharp").
>>>>
>>>> Neither of these questions has anything to do with the "phase noise"
>>>> specification.
>>>>
>>>> John Ragle -- W1ZI
>>>> ______________________________________________________________
>>>> Elecraft mailing list
>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>> Post: mailto:[hidden email]
>>>>
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
>

Geoffrey Mackenzie-Kennedy

Re: XG3 device...

In reply to this post by Alan Bloom

Hi Al,

You did say "normally not an issue", but when making even or odd order
intermodulation measurements on a receiver the use of RF sources whose
harmonic content is significant can and usually will lead to invalid
results.

73,
Geoff
GM4ESD

On April 14, 2011 at 22:58 +0100, Alan Bloom wrote:

Alan Bloom

Re: XG3 device...

Hi Geoff,

Most receivers have bandpass and/or low-pass filters in the front end
that would filter out the harmonics of a square-wave test signal. I
could dream up some unusual situations where the harmonics could cause a
problem, but normally it would not be an issue.

Alan N1AL

On Fri, 2011-04-15 at 00:37 +0100, Geoffrey Mackenzie-Kennedy wrote:

> Hi Al,
>
> You did say "normally not an issue", but when making even or odd order
> intermodulation measurements on a receiver the use of RF sources whose
> harmonic content is significant can and usually will lead to invalid
> results.
>
> 73,
> Geoff
> GM4ESD
>
>
> On April 14, 2011 at 22:58 +0100, Alan Bloom wrote:
>
> > Hi Jack,
> >
> > You're right that when testing a wide-band device like an amplifier you
> > have to filter out the generator harmonics in order to get a valid
> > third-order IMD test. But when testing a narrow-band device like a
> > receiver the harmonics are normally not an issue.
> >
> > Those Coilcraft low-pass filters look very nice, especially for he
> > price. Where can you buy them?
> >
> > Alan N1AL
> >
> >
> > On Thu, 2011-04-14 at 16:54 -0400, Jack Smith wrote:
> >> Alan:
> >>
> >> One are where a square wave RF source can get you into trouble is 2nd
> >> and 3rd order intermodulation measurements.
> >>
> >> Mini-Circuits Ap Note 00008 discusses the reason why.
> >> http://www.minicircuits.com/pages/pdfs/AN00008.pdf
> >>
> >> I usually use an outboard low pass filter on my HP 8657A signal
> >> generators when making IMD measurements of high performance amplifiers,
> >> and it's not a bad idea even with HP 8640B generators which are 60 dB+
> >> down on the harmonics.
> >>
> >> As far as a low pass filter goes, CoilCraft has some very inexpensive
> >> ($3 range) 7th order elliptical low pass filter modules, the P7LP
> >> series, with cutoff frequencies from 300 KHz to 500 MHz.
> >> http://www.coilcraft.com/pdfs/lcfilt.pdf These are perfectly fine for
> >> output filtering of a single generator, but should not be used with
> >> multiple signals as they can themselves be intermod generators. I use
> >> them here for various tasks including signal generator clean up.
> >>
> >> If anyone is interested, I have a few extra printed circuit boards with
> >> provisions for PCB-mount BNC connectors and a P7LP filter and can make
> >> them available at a reasonable price (PCB only, you supply the
> >> connectors and filter modules). Usual double sided, silk screen, solder
> >> masked boards. I have installed a socket strip in one as an experiment
> >> so that one might just plug in the appropriate filter, but that's not a
> >> great idea as the filter modules are not all that mechanically robust
> >> and the extra lead inductance from the socket degrades stop band
> >> performance at higher frequencies. I can send a photo of the board to
> >> anyone interested.
> >>
> >> Jack K8ZOA
>
>
>
>

Geoffrey Mackenzie-Kennedy

Re: XG3 device...

Hi Alan,

Indeed, most receivers do have some form of filter "up front" in the front
end, and therein lies one source of IMD measurement error if harmonics are
present in the applied test signals.

While the MiniCircuits application note AN-00-008 which Jack mentioned
points out that harmonics present in the applied test signals are a
potential source of error when measuring the IMD performance of a device
such as a mixer, for the same reasons error can be introduced by a
receiver's input filter(s). So it is essential that "clean" sources are used
when testing a receiver.

73,
Geoff
GM4ESD

On April 15, 2011 at 04:26 +0100, Alan Bloom wrote:

> Hi Geoff,
>
> Most receivers have bandpass and/or low-pass filters in the front end
> that would filter out the harmonics of a square-wave test signal. I
> could dream up some unusual situations where the harmonics could cause a
> problem, but normally it would not be an issue.
>
> Alan N1AL
>
>
> On Fri, 2011-04-15 at 00:37 +0100, Geoffrey Mackenzie-Kennedy wrote:
>> Hi Al,
>>
>> You did say "normally not an issue", but when making even or odd order
>> intermodulation measurements on a receiver the use of RF sources whose
>> harmonic content is significant can and usually will lead to invalid
>> results.
>>
>> 73,
>> Geoff
>> GM4ESD
>>
>>
>> On April 14, 2011 at 22:58 +0100, Alan Bloom wrote:
>>
>> > Hi Jack,
>> >
>> > You're right that when testing a wide-band device like an amplifier you
>> > have to filter out the generator harmonics in order to get a valid
>> > third-order IMD test. But when testing a narrow-band device like a
>> > receiver the harmonics are normally not an issue.
>> >
>> > Those Coilcraft low-pass filters look very nice, especially for he
>> > price. Where can you buy them?
>> >
>> > Alan N1AL

Alan Bloom

Re: XG3 device...

Hi Geoff,

I guess I don't understand. Filters are linear devices. How can they
cause IMD? If the signal generator's harmonics are removed by the
receiver filters then it is the same as if the sig gen were "clean", no?

73,

Alan N1AL

On Fri, 2011-04-15 at 11:54 +0100, Geoffrey Mackenzie-Kennedy wrote:

> Hi Alan,
>
> Indeed, most receivers do have some form of filter "up front" in the front
> end, and therein lies one source of IMD measurement error if harmonics are
> present in the applied test signals.
>
> While the MiniCircuits application note AN-00-008 which Jack mentioned
> points out that harmonics present in the applied test signals are a
> potential source of error when measuring the IMD performance of a device
> such as a mixer, for the same reasons error can be introduced by a
> receiver's input filter(s). So it is essential that "clean" sources are used
> when testing a receiver.
>
> 73,
> Geoff
> GM4ESD
>
>
> On April 15, 2011 at 04:26 +0100, Alan Bloom wrote:
>
> > Hi Geoff,
> >
> > Most receivers have bandpass and/or low-pass filters in the front end
> > that would filter out the harmonics of a square-wave test signal. I
> > could dream up some unusual situations where the harmonics could cause a
> > problem, but normally it would not be an issue.
> >
> > Alan N1AL
> >
> >
> > On Fri, 2011-04-15 at 00:37 +0100, Geoffrey Mackenzie-Kennedy wrote:
> >> Hi Al,
> >>
> >> You did say "normally not an issue", but when making even or odd order
> >> intermodulation measurements on a receiver the use of RF sources whose
> >> harmonic content is significant can and usually will lead to invalid
> >> results.
> >>
> >> 73,
> >> Geoff
> >> GM4ESD
> >>
> >>
> >> On April 14, 2011 at 22:58 +0100, Alan Bloom wrote:
> >>
> >> > Hi Jack,
> >> >
> >> > You're right that when testing a wide-band device like an amplifier you
> >> > have to filter out the generator harmonics in order to get a valid
> >> > third-order IMD test. But when testing a narrow-band device like a
> >> > receiver the harmonics are normally not an issue.
> >> >
> >> > Those Coilcraft low-pass filters look very nice, especially for he
> >> > price. Where can you buy them?
> >> >
> >> > Alan N1AL
>
>
>

Jack Smith-6

Re: XG3 device...

Only to a first approximation are filters linear.

Usually the major source of non-linearity is in the inductors. Even
powdered iron is non-linear to some degree. Ferrite is worse, of course.
Air is pretty close to perfect.

Capacitors are also non-linear at some level, as C is not constant with
applied voltage. NP0/C0G caps are very good, but again not perfect.

Filter generated intermodulation problems are real and measurable. Been
there and done that and have the Tee-shirt.

Jack K8ZOA

On 4/15/2011 1:01 PM, Alan Bloom wrote:

> Hi Geoff,
>
> I guess I don't understand. Filters are linear devices. How can they
> cause IMD? If the signal generator's harmonics are removed by the
> receiver filters then it is the same as if the sig gen were "clean", no?
>
> 73,
>
> Alan N1AL
>
>
> On Fri, 2011-04-15 at 11:54 +0100, Geoffrey Mackenzie-Kennedy wrote:
>> Hi Alan,
>>
>> Indeed, most receivers do have some form of filter "up front" in the front
>> end, and therein lies one source of IMD measurement error if harmonics are
>> present in the applied test signals.
>>
>> While the MiniCircuits application note AN-00-008 which Jack mentioned
>> points out that harmonics present in the applied test signals are a
>> potential source of error when measuring the IMD performance of a device
>> such as a mixer, for the same reasons error can be introduced by a
>> receiver's input filter(s). So it is essential that "clean" sources are used
>> when testing a receiver.
>>
>> 73,
>> Geoff
>> GM4ESD
>>
>>
>> On April 15, 2011 at 04:26 +0100, Alan Bloom wrote:
>>
>>> Hi Geoff,
>>>
>>> Most receivers have bandpass and/or low-pass filters in the front end
>>> that would filter out the harmonics of a square-wave test signal. I
>>> could dream up some unusual situations where the harmonics could cause a
>>> problem, but normally it would not be an issue.
>>>
>>> Alan N1AL
>>>
>>>
>>> On Fri, 2011-04-15 at 00:37 +0100, Geoffrey Mackenzie-Kennedy wrote:
>>>> Hi Al,
>>>>
>>>> You did say "normally not an issue", but when making even or odd order
>>>> intermodulation measurements on a receiver the use of RF sources whose
>>>> harmonic content is significant can and usually will lead to invalid
>>>> results.
>>>>
>>>> 73,
>>>> Geoff
>>>> GM4ESD
>>>>
>>>>
>>>> On April 14, 2011 at 22:58 +0100, Alan Bloom wrote:
>>>>
>>>>> Hi Jack,
>>>>>
>>>>> You're right that when testing a wide-band device like an amplifier you
>>>>> have to filter out the generator harmonics in order to get a valid
>>>>> third-order IMD test. But when testing a narrow-band device like a
>>>>> receiver the harmonics are normally not an issue.
>>>>>
>>>>> Those Coilcraft low-pass filters look very nice, especially for he
>>>>> price. Where can you buy them?
>>>>>
>>>>> Alan N1AL
>>
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Guy, K2AV

Re: XG3 device...

Of course, if we didn't want to be able to copy with equal clarity
over a > 100 dB input signal range, we could dispense with a lot of
this. AND do that with signals of the extremes separated by a mere 250
Hz. We are so picky. Why does anyone put up with us :>)

You selling that T-shirt in bulk?

73, Guy.

On Fri, Apr 15, 2011 at 1:11 PM, Jack Smith
<[hidden email]> wrote:

> Only to a first approximation are filters linear.
>
> Usually the major source of non-linearity is in the inductors. Even
> powdered iron is non-linear to some degree. Ferrite is worse, of course.
> Air is pretty close to perfect.
>
> Capacitors are also non-linear at some level, as C is not constant with
> applied voltage. NP0/C0G caps are very good, but again not perfect.
>
> Filter generated intermodulation problems are real and measurable. Been
> there and done that and have the Tee-shirt.
>
> Jack K8ZOA
>
>
> On 4/15/2011 1:01 PM, Alan Bloom wrote:
>> Hi Geoff,
>>
>> I guess I don't understand. Filters are linear devices. How can they
>> cause IMD? If the signal generator's harmonics are removed by the
>> receiver filters then it is the same as if the sig gen were "clean", no?
>>
>> 73,
>>
>> Alan N1AL
>>
>>
>> On Fri, 2011-04-15 at 11:54 +0100, Geoffrey Mackenzie-Kennedy wrote:
>>> Hi Alan,
>>>
>>> Indeed, most receivers do have some form of filter "up front" in the front
>>> end, and therein lies one source of IMD measurement error if harmonics are
>>> present in the applied test signals.
>>>
>>> While the MiniCircuits application note AN-00-008 which Jack mentioned
>>> points out that harmonics present in the applied test signals are a
>>> potential source of error when measuring the IMD performance of a device
>>> such as a mixer, for the same reasons error can be introduced by a
>>> receiver's input filter(s). So it is essential that "clean" sources are used
>>> when testing a receiver.
>>>
>>> 73,
>>> Geoff
>>> GM4ESD
>>>
>>>
>>> On April 15, 2011 at 04:26 +0100, Alan Bloom wrote:
>>>
>>>> Hi Geoff,
>>>>
>>>> Most receivers have bandpass and/or low-pass filters in the front end
>>>> that would filter out the harmonics of a square-wave test signal. I
>>>> could dream up some unusual situations where the harmonics could cause a
>>>> problem, but normally it would not be an issue.
>>>>
>>>> Alan N1AL
>>>>
>>>>
>>>> On Fri, 2011-04-15 at 00:37 +0100, Geoffrey Mackenzie-Kennedy wrote:
>>>>> Hi Al,
>>>>>
>>>>> You did say "normally not an issue", but when making even or odd order
>>>>> intermodulation measurements on a receiver the use of RF sources whose
>>>>> harmonic content is significant can and usually will lead to invalid
>>>>> results.
>>>>>
>>>>> 73,
>>>>> Geoff
>>>>> GM4ESD
>>>>>
>>>>>
>>>>> On April 14, 2011 at 22:58 +0100, Alan Bloom wrote:
>>>>>
>>>>>> Hi Jack,
>>>>>>
>>>>>> You're right that when testing a wide-band device like an amplifier you
>>>>>> have to filter out the generator harmonics in order to get a valid
>>>>>> third-order IMD test. But when testing a narrow-band device like a
>>>>>> receiver the harmonics are normally not an issue.
>>>>>>
>>>>>> Those Coilcraft low-pass filters look very nice, especially for he
>>>>>> price. Where can you buy them?
>>>>>>
>>>>>> Alan N1AL
>>>
>>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Alan Bloom

Re: XG3 device...

In reply to this post by Jack Smith-6

Sure, but if the filters are non-linear that's a whole different problem
that has nothing to do with harmonics in the signal source.

The question was whether signal generator harmonics are normally a
problem when measuring a receiver. I claim they are not because they
are removed by the filters in the receiver front end.

When I was working in the R&D lab of the Hewlett Packard Signal Sources
division, one of our competitors came out with a new signal generator
with digital modulation. The modulation was generated at an IF which
was heterodyned up to microwave frequencies without any filtering to
remove the image. So there was a zero-dB spur X MHz away from the
desired signal. They got away with it because it was far enough away to
be filtered out by the receiver under test.

Alan N1AL

On Fri, 2011-04-15 at 13:11 -0400, Jack Smith wrote:

> Only to a first approximation are filters linear.
>
> Usually the major source of non-linearity is in the inductors. Even
> powdered iron is non-linear to some degree. Ferrite is worse, of
> course. Air is pretty close to perfect.
>
> Capacitors are also non-linear at some level, as C is not constant
> with applied voltage. NP0/C0G caps are very good, but again not
> perfect.
>
> Filter generated intermodulation problems are real and measurable.
> Been there and done that and have the Tee-shirt.
>
> Jack K8ZOA
>
>
> On 4/15/2011 1:01 PM, Alan Bloom wrote:
> > Hi Geoff,
> >
> > I guess I don't understand. Filters are linear devices. How can they
> > cause IMD? If the signal generator's harmonics are removed by the
> > receiver filters then it is the same as if the sig gen were "clean", no?
> >
> > 73,
> >
> > Alan N1AL
> >
> >
> > On Fri, 2011-04-15 at 11:54 +0100, Geoffrey Mackenzie-Kennedy wrote:
> > > Hi Alan,
> > >
> > > Indeed, most receivers do have some form of filter "up front" in the front
> > > end, and therein lies one source of IMD measurement error if harmonics are
> > > present in the applied test signals.
> > >
> > > While the MiniCircuits application note AN-00-008 which Jack mentioned
> > > points out that harmonics present in the applied test signals are a
> > > potential source of error when measuring the IMD performance of a device
> > > such as a mixer, for the same reasons error can be introduced by a
> > > receiver's input filter(s). So it is essential that "clean" sources are used
> > > when testing a receiver.
> > >
> > > 73,
> > > Geoff
> > > GM4ESD
> > >
> > >
> > > On April 15, 2011 at 04:26 +0100, Alan Bloom wrote:
> > >
> > > > Hi Geoff,
> > > >
> > > > Most receivers have bandpass and/or low-pass filters in the front end
> > > > that would filter out the harmonics of a square-wave test signal. I
> > > > could dream up some unusual situations where the harmonics could cause a
> > > > problem, but normally it would not be an issue.
> > > >
> > > > Alan N1AL
> > > >
> > > >
> > > > On Fri, 2011-04-15 at 00:37 +0100, Geoffrey Mackenzie-Kennedy wrote:
> > > > > Hi Al,
> > > > >
> > > > > You did say "normally not an issue", but when making even or odd order
> > > > > intermodulation measurements on a receiver the use of RF sources whose
> > > > > harmonic content is significant can and usually will lead to invalid
> > > > > results.
> > > > >
> > > > > 73,
> > > > > Geoff
> > > > > GM4ESD
> > > > >
> > > > >
> > > > > On April 14, 2011 at 22:58 +0100, Alan Bloom wrote:
> > > > >
> > > > > > Hi Jack,
> > > > > >
> > > > > > You're right that when testing a wide-band device like an amplifier you
> > > > > > have to filter out the generator harmonics in order to get a valid
> > > > > > third-order IMD test. But when testing a narrow-band device like a
> > > > > > receiver the harmonics are normally not an issue.
> > > > > >
> > > > > > Those Coilcraft low-pass filters look very nice, especially for he
> > > > > > price. Where can you buy them?
> > > > > >
> > > > > > Alan N1AL
> > >
> > >
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >

Scott Ellington

Re: XG3 device...

In reply to this post by Guy, K2AV

Is there any other communication system that requires the kind of close-in dynamic range we do? It certainly wouldn't make much sense to design a commercial system with such requirements. It seems likely we hams have the toughest receiver dynamic range requirements on the planet.

Scott K9MA

On Apr 15, 2011, at 12:30 PM, Guy Olinger K2AV wrote:

> Of course, if we didn't want to be able to copy with equal clarity
> over a > 100 dB input signal range, we could dispense with a lot of
> this. AND do that with signals of the extremes separated by a mere 250
> Hz. We are so picky. Why does anyone put up with us :>)

Scott Ellington
Madison, Wisconsin
USA

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Geoffrey Mackenzie-Kennedy

Re: XG3 device...

In reply to this post by Alan Bloom

Hi Alan,

Sorry that I was not here to reply to your previous e-mail.

With respect, filter non-linearity and the level of harmonics coming from
the signal sources are related in terms of the amplitude of the IMD products
seen at the output of the filter.

If the receiver being tested is perfect and linear, obviously it would not
matter if the IMD test sources contained harmonics because, for example, the
fundamental of one source (F1) has nowhere to mix with the second harmonic
of the second source (2F2) to produce the third order product 2F2-F1 -
assuming there is no IMD contribution from the test equipment.

On the other hand if the receiver's signal path passes through a non-linear
element such as an input filter, then of course there is 'mixer' available
inside the filter to produce the natural third order product 2F2 - F1 as
would be expected when using clean sources. If the sources produce harmonics
however, then a twin third order product also at 2F2 - F1 would also be
generated, where 2F2 is the second harmonic generated by the F2 source. The
composite level of these two third order product as seen at the filter's
output could be significantly different from that of the natural product
depending on how they add.

Although the second harmonic of a test source should be greatly attenuated
by a typical front end filter, an unwanted 'mixer' can exist near the input
of the filter, for example in the form of an inductor's core, and would be
exposed to the full impact of the source's harmonics.

Geoff
GM4ESD

On Friday, April 15, 2011, at 18:45 +0100, Alan Bloom wrote:

> Sure, but if the filters are non-linear that's a whole different problem
> that has nothing to do with harmonics in the signal source.
>
> The question was whether signal generator harmonics are normally a
> problem when measuring a receiver. I claim they are not because they
> are removed by the filters in the receiver front end.
>
> When I was working in the R&D lab of the Hewlett Packard Signal Sources
> division, one of our competitors came out with a new signal generator
> with digital modulation. The modulation was generated at an IF which
> was heterodyned up to microwave frequencies without any filtering to
> remove the image. So there was a zero-dB spur X MHz away from the
> desired signal. They got away with it because it was far enough away to
> be filtered out by the receiver under test.
>
> Alan N1AL
>
>
> On Fri, 2011-04-15 at 13:11 -0400, Jack Smith wrote:
>> Only to a first approximation are filters linear.
>>
>> Usually the major source of non-linearity is in the inductors. Even
>> powdered iron is non-linear to some degree. Ferrite is worse, of
>> course. Air is pretty close to perfect.
>>
>> Capacitors are also non-linear at some level, as C is not constant
>> with applied voltage. NP0/C0G caps are very good, but again not
>> perfect.
>>
>> Filter generated intermodulation problems are real and measurable.
>> Been there and done that and have the Tee-shirt.
>>
>> Jack K8ZOA
>>
>>
>> On 4/15/2011 1:01 PM, Alan Bloom wrote:
>> > Hi Geoff,
>> >
>> > I guess I don't understand. Filters are linear devices. How can they
>> > cause IMD? If the signal generator's harmonics are removed by the
>> > receiver filters then it is the same as if the sig gen were "clean",
>> > no?
>> >
>> > 73,
>> >
>> > Alan N1AL

alorona

Re: XG3 device...

Geoff, you're right. But I gather you're talking about two closely-spaced
sources?

I think the original question was whether harmonics from a *single* source would
be a real problem. After all, this thread was originally about the XG3.

Generally, any harmonics aren't going to be a real big problem. They'll be
well-filtered by the time they get to the real nonlinearities in a receiver.

And even if they're not, consider a 7 MHz signal coming out of an XG3 along with
a 2nd harmonic at 14 MHz.

The third order mixing products will be at 0 and 21 MHz. This will only be
dangerous if the receiver is either a zero-IF design or has very poor front end
rejection.

The problem might get a little worse as you go down to 160 meters, but even then
the 3rd order product will be at 5.4 MHz, which any 160m receiver worth its salt
should be able to reject.

Al W6LX
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