On Thu, Aug 4, 2022 at 04:46 PM, Neil Smith G4DBN wrote:
Nice! Never heard of it being called that, but it fits.? I guess a bit of code would allow the frequency and the exponential value to be extracted and also make corrections based on calibrations with known standard inductors.? Might start to get a bit too exciting above a few MHz, dealing with stray capacitance/inductance, but for MF/LF/VLF and audio, it might be a simple unit to build.
Neil
There's a pretty comprehensive document about Q-measurements by Andrew Gregory at NPL. /g/Test-Equipment-Design-Construction/files/Q-factor%20%28Q%20is%20the%20inverse%20of%20dissipation%20factor%20DF%29./Q-factor%20measurement%20by%20using%20a%20Vector%20Network%20Analyser.%20NPL%20Report.%20MAT%2058%20by%20Gregory,%20A%20P%20%282021%29/Gregory,%20A%20P%20%282021%29%20Q-factor%20measurement%20by%20using%20a%20Vector%20Network%20Analyser.%20NPL%20Report.%20MAT%2058.pdfI have emailed and spoken to him before about some RF measurements. Also has a look around his lab. There it mentions The Q-factor of a resonator is defined by Q = 2πU/?U where U is the average energy stored by the resonator and ?U is the decrease in the average stored energy per wave cycle at the resonant frequency [1]. Time-domain (“ring 诲辞飞苍”) methods [2] enable measurement of the loadedQ-factor QL, in which U and ?U pertain to the entire system comprising of the resonator and the instrument that is used for observing resonances. The time-domain method requires excitation of a resonance followed by a measurement of the exponential decay of the amplitude (or stored energy). Methods of performing time-domain Q-factor measurements are described in references [14–16].
Links to those references are [14[ [15]? [16]
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Back when the The Radio Board was running, an Ebay seller mkmak222 sold a Ring Down Q meter populated pcb that with a couple additions made a complete Q meter.
I don't find it on his Ebay sales page and I have sent him a letter asking for more info and will relate it when I get more info. I did find a couple of videos showing the only the backside of the pcb. Not much info, just shows measurement of a high Q coil. https://www.youtube.com/watch?v=gUzk1aGljqQ
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On 05/08/2022 10:33, Dr. David Kirkby,
Kirkby Microwave Ltd wrote:
Do you have a copy of the paper
Darko Kajfez “Q Factor Measurements, Analog and Digital,” darko/rfqmeas2b.pdf
Try
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On Thu, Aug 4, 2022 at 12:30 PM, Jacques Audet wrote:
Hello everyone,
You may want to have a look at this article that I wrote in QEX, ten
years ago:
Q Factor Measurements on L-C Circuits.
Jacques,? VE2AZX
Thank you. I see your paper mentioned somewhere, but no link was given. Do you have a copy of the paper Darko Kajfez “Q Factor Measurements, Analog and Digital,” www.ee.olemiss.edu/darko/rfqmeas2b.pdfyou mention? I can't get any response from the server whatsoever - not even an error message. Looking at your paper briefly, I would have thought figure 4 would be inaccurate if the ESR is below about 5-10 ohm, as VNAs are not good with high reflection coefficients. Do you have a more general formula for equation 4, taking into account different values of coupling capacitors? Although it's not hard to make capacitors of around 1 pF, getting two to have the same capacitance is not going to be easy. I would have thought there were some practical problems with your SWR method. The Boonton Q-meters have a capacitor of around 400 pF from memory. If one is using that to resonate an inductor, and one needs a variable matching capacitor of 10 to 50 x higher, that means 4 nF to 20 nF. One is not going to be able to get a variable capacitor of that value very easily. It seems a tricky problem making an accurate Q-meter, as you don't have access to standards with a very low uncertainty. I believe the Boonton ones are around 2% uncertainty.
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Back in the days of arc and spark there was a thing called a decrimeter.? This was a sort of wave meter used to measure the degree of "damping" of a transmitted signal.? ?Really it's bandwidth. Damped wave spark transmitters could be pretty broad.? In effect it was used to measure the Q of the output tuned circuits but I am not sure the concept of Q existed then. If so it was pretty exotic.? ?In effect the decremeter was used to measure the half power points of the signal and determine the "decrement"by means of a chart.? I think the most common ones wrw made by Kolster, who also made an early marine direction finder.
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-------- Original message -------- From: "Brooke Clarke via groups.io" <brooke@...> Date: 8/4/22 6:18 PM (GMT-08:00) Subject: Re: [Test Equipment Design & Construction] Making a Q-meter /
Hi Neil:
I have a flyback tester that works by counting the ringing.
Shorted turns kill the Q and so this works quite well.
A modified version would simply have a digital display with the
count.
--
Have Fun,
Brooke Clarke
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
Possibly a silly question, but have any Q meters been built that
use the other approach of watching the relaxation decay starting
with a forced excitation and calculating the dissipation factor??
Most of the inductors I'm working with at LF/VLF have a Q of 300
or more, so would it be feasible to resonate one with a very high
performance capacitor, tune a power oscillator to the resonance
peak automatically, then disconnect it at a zero crossing and
capture the decaying oscillation with a fast high impedance ADC
and process it to determine the Q based on the envelope decay??
Indeed, would a single voltage or current pulse suffice as the
excitation rather than an oscillator? A quick simulation suggests
that it is feasible. With a resonance at 150 kHz and a Q of 300,
the envelope amplitude falls to about exp(-pi), around 4%, after 2
ms, or 300 cycles, which is another way to define Q factor.
|
To get 1 mOhm, place five 5 mOhms resistors in parallel (Mouser <>)
preferably in a circle around the inductor drive terminal.
Drive the 1 mOhn resistor with a stepdown transfer, 10:1 perhaps. For the ringdown method, the freq response flatness doesn't matter. Different transformers can be switched in if necessary.
For the ringdown method drive a transistor switch with a narrow pulse at a very low rep rate.
For the conventional Q Meter with oscillator at the resonant freq, use a RF amp with much lower output impedance than 50 ohms, sense the voltage across the 1 mOhm resistor, and provide a voltage leveling circuit.
Alternatively, one could simply measure the voltage across the 1 mOhm resistor to use calculating the Q rather than assume a fixed value.
Another method of measuring Q:
An article by Jacques Audet in the Jan/Feb 2012 issue of QEX <> lists a method of measuring Q by the attenuation of a series tuned LC circuit in series with the generator output impedance. The Q measurement Accuracy is limited by the accuracy one can measure the signal levels. A 0.13 db delta measurement error causes about a 1% Q calculation error.
John
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On 8/4/2022 1:19 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote: I am looking at the possibility of making a Q meter for the frequency range 1.5 MHz to 150 MHz. One common way to do this is to inject a voltage from a LOW impedance source, into a series tuned circuit, then measure the voltage developed across the tuned circuit with a high input impedance voltmeter. The Q is the ratio of those two voltages.
Designs for Q meters usually include an oscillator, but I don’t think I will bother with that as I can easily use a signal generator.
One design appeared in Practical Wireless in the November 1978 issue. I stuck a copy of that in a sub-directory for Q measurements in the files section of the forum
/g/Test-Equipment-Design-Construction/files/Q-factor%20%28Q%20is%20the%20inverse%20of%20dissipation%20factor%20DF%29 </g/Test-Equipment-Design-Construction/files/Q-factor%20%28Q%20is%20the%20inverse%20of%20dissipation%20factor%20DF%29>. </g/Test-Equipment-Design-Construction/files/Q-factor%20%28Q%20is%20the%20inverse%20of%20dissipation%20factor%20DF%29.>
There are two problems I see with that design
1) The meter has measurement ranges of only 0-20 and 0-100, but many inductors have Q’s much higher than 100. The HP 4342A can measure Qs from 5 to 1000. The old Boonton 160-A measures Q up to 640 (from memory).
2) The output impedance of source is too high?- it is approximately 2 ohm on the Q=0-20 range and 10.2?ohm on the Q=0-100 range.
Can anyone think of a way of turning a signal generator to have an output impedance of 1 milli ohm? I think I have a 5 W Minicircuits amplifier around, so I can afford to waste a bit in heat. But it is not practical to put 50 ohm in series with 1 milli ohm to terminate the amplifier in the required 50 ohm. I will have so little voltage left, it will be difficult to measure the output voltage, even though it’s multipled by the Q of the coil.
A step-down transformer seems the most obvious way, but that requires a turns ratio of sqrt(50000)=224. Even with a single turn on the secondary, there will be too many turns on the primary for this to work at 150 MHz.
I have not yet looked at the HP 4343A meter service manual. That will probably give me some ideas.
I suspect the answer is to not try to get such a low output impedance, accept that the voltage generated across the LC combination will be less than the Q, and correct for that in software.
Any other thoughts?
*PS, Does anyone have any documentation, apart from the user manual, on the HP 42851A Q-adapter, which is used with the HP/Agilent 4285A Precision LCR meter? *
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Hi Neil:
I have a flyback tester that works by counting the ringing.
Shorted turns kill the Q and so this works quite well.
A modified version would simply have a digital display with the
count.
--
Have Fun,
Brooke Clarke
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
toggle quoted message
Show quoted text
Possibly a silly question, but have any Q meters been built that
use the other approach of watching the relaxation decay starting
with a forced excitation and calculating the dissipation factor??
Most of the inductors I'm working with at LF/VLF have a Q of 300
or more, so would it be feasible to resonate one with a very high
performance capacitor, tune a power oscillator to the resonance
peak automatically, then disconnect it at a zero crossing and
capture the decaying oscillation with a fast high impedance ADC
and process it to determine the Q based on the envelope decay??
Indeed, would a single voltage or current pulse suffice as the
excitation rather than an oscillator? A quick simulation suggests
that it is feasible. With a resonance at 150 kHz and a Q of 300,
the envelope amplitude falls to about exp(-pi), around 4%, after 2
ms, or 300 cycles, which is another way to define Q factor.
|
Nice! Never heard of it being called
that, but it fits.? I guess a bit of code would allow the
frequency and the exponential value to be extracted and also make
corrections based on calibrations with known standard inductors.?
Might start to get a bit too exciting above a few MHz, dealing
with stray capacitance/inductance, but for MF/LF/VLF and audio, it
might be a simple unit to build.
Neil
On 05/08/2022 00:34, Steve Ratzlaff
wrote:
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This Swiss guy has had an article about the ring down test for
Q for a number of years.
73,
Steve AA7U
On 8/4/2022 4:30 PM, Neil Smith G4DBN
wrote:
Possibly a silly question, but have any Q meters been built that
use the other approach of watching the relaxation decay starting
with a forced excitation and calculating the dissipation
factor?? Most of the inductors I'm working with at LF/VLF have a
Q of 300 or more, so would it be feasible to resonate one with a
very high performance capacitor, tune a power oscillator to the
resonance peak automatically, then disconnect it at a zero
crossing and capture the decaying oscillation with a fast high
impedance ADC and process it to determine the Q based on the
envelope decay?? Indeed, would a single voltage or current pulse
suffice as the excitation rather than an oscillator? A quick
simulation suggests that it is feasible. With a resonance at 150
kHz and a Q of 300, the envelope amplitude falls to about
exp(-pi), around 4%, after 2 ms, or 300 cycles, which is another
way to define Q factor.
_._,_._,_
|
This Swiss guy has had an article about the ring down test for Q
for a number of years.
73,
Steve AA7U
On 8/4/2022 4:30 PM, Neil Smith G4DBN
wrote:
toggle quoted message
Show quoted text
Possibly a silly question, but have any Q meters been built that
use the other approach of watching the relaxation decay starting
with a forced excitation and calculating the dissipation factor??
Most of the inductors I'm working with at LF/VLF have a Q of 300
or more, so would it be feasible to resonate one with a very high
performance capacitor, tune a power oscillator to the resonance
peak automatically, then disconnect it at a zero crossing and
capture the decaying oscillation with a fast high impedance ADC
and process it to determine the Q based on the envelope decay??
Indeed, would a single voltage or current pulse suffice as the
excitation rather than an oscillator? A quick simulation suggests
that it is feasible. With a resonance at 150 kHz and a Q of 300,
the envelope amplitude falls to about exp(-pi), around 4%, after 2
ms, or 300 cycles, which is another way to define Q factor.
|
Possibly a silly question, but have any Q meters been built that use
the other approach of watching the relaxation decay starting with a
forced excitation and calculating the dissipation factor?? Most of
the inductors I'm working with at LF/VLF have a Q of 300 or more, so
would it be feasible to resonate one with a very high performance
capacitor, tune a power oscillator to the resonance peak
automatically, then disconnect it at a zero crossing and capture the
decaying oscillation with a fast high impedance ADC and process it
to determine the Q based on the envelope decay?? Indeed, would a
single voltage or current pulse suffice as the excitation rather
than an oscillator? A quick simulation suggests that it is feasible.
With a resonance at 150 kHz and a Q of 300, the envelope amplitude
falls to about exp(-pi), around 4%, after 2 ms, or 300 cycles, which
is another way to define Q factor.
|
On Thu, 4 Aug 2022 at 22:34, Richard Knoppow < dickburk@...> wrote: ???? Someone suggested getting the handbook for the Boonton 260
Q-Meter. Since Boonton did this already perhaps you can get some
inspiration from it. Of course its tubes but nonetheless one can
use the same principles for SS. Also look at the type 190, the
VHF version of the Q-Meter. Essentially both use a constant
current source to drive the test circuit. Also, download the set
of Boonton newsletters, which are available at the -hp- archive
where the handbook is. Boonton more or less invented the Q meter
and wrote a lot about its theory of operation.
??? A note: The meter scale is matched to the amplifier. Usually,
the amplifier has an extremely long life but both go together.
For this reason the solid state replacement for the tube will
probably not match the meter scale.
So are you saying that the scale on the meter is not linear, so each one was individually made to take into account the specific non-linearity of the tube??
??? If you obtain a Q-Meter also find some standard coils to
check its calibration. They are quite accurate. Note that Boonton
supplied both "standard" and "working" coils. The "working" coils
are very convenient to have but one can make them. The Boonton
coils are very high Q. The "standard" coils are calibrated for Q,
and resonant capacitance.
I have bought a 518-A5 coil (50 kHz -150 kHz) and 518-A4 (150 kHz - 450 kHz). I would particularly like to find a 518-A1 (15 MHz to 45 MHz). No doubt I will buy some others - just depends what comes up at the right price. Those are the recommended ones for the HP 4342A. I expect that I will buy one of them. I just need to get one at the right price.? -- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@...Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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Someone suggested getting the handbook for the Boonton 260 Q-Meter. Since Boonton did this already perhaps you can get some inspiration from it. Of course its tubes but nonetheless one can use the same principles for SS. Also look at the type 190, the VHF version of the Q-Meter. Essentially both use a constant current source to drive the test circuit. Also, download the set of Boonton newsletters, which are available at the -hp- archive where the handbook is. Boonton more or less invented the Q meter and wrote a lot about its theory of operation.
?? A note: The meter scale is matched to the amplifier. Usually, the amplifier has an extremely long life but both go together. For this reason the solid state replacement for the tube will probably not match the meter scale.
?? If you obtain a Q-Meter also find some standard coils to check its calibration. They are quite accurate. Note that Boonton supplied both "standard" and "working" coils. The "working" coils are very convenient to have but one can make them. The Boonton coils are very high Q. The "standard" coils are calibrated for Q, and resonant capacitance.
??? I found on the Q-Meters I have dealt with that the oscillators are quite well calibrated. I think there is really only one setting that gets all ranges on frequency. Be careful of the adustment for the capacitor. It should really be set with a standard coil that resonates near the minimum capacitance. These things have become somewhat of orphans because they are "old fashioned" but in fact they are extremely useful.
??? I will put in a good word for the Boonton RX meter also. A one piece impedance bridge with oscillator, bridge and detector in one box. Unfortunately mine came a cropper by falling off a table. Too bad. As with the Q-Meter the internal oscillator is usually very well calibrated and, again, Boonton published a very good handbook and lots of application notes.
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On 8/4/2022 8:41 AM, Oz-in-DFW wrote: On 8/4/2022 3:19 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
Can anyone think of a way of turning a signal generator to have an output impedance of 1 milli ohm? Like most engineering decisions, it depends.? In this case my first though would be negative feedback around an amp.? You can get /almost/ arbitrary reduction of output impedance as a tradeoff for other parameters.? This is much more practical at much higher frequencies than years past.
At frequencies where? negative feedback is not practical, conventional transformers are not terribly likely to useful or practical.? It may be that the kind of transformers used in RF power amplifiers may be as they can be matching sub one ohm impedances to 50 ohms.
Finally, filter structures can achieve wide impedance transformations.? Of couirse these are subject the practical limitations of components.? Since you are focusing on output impedance you are likely to make different optimizations are so find the impedance transformations you wish more achievable.
Oz (in DFW, Texas)
--
Richard Knoppow
dickburk@...
WB6KBL
|
?
?
Reading that, I do get the feeling that some of the improvements made between the 160-A and 260-A, would not be necessary if an instrument was made with a microprocessor doing some number?crunching. For example, they reduced the injection resistor from 40 milli ohm to 20 milli ohm. But still it’s a source of error at high Q which one can correct with the aid of a calculation. If an instrument was made nowadays, one might just as well correct every reading ?Maybe the resistors used in the PW design would be okay if a microprocessor did the corrections, rather than
A digital display would definitely contribute to the accuracy of repeated measurements, but I would still
maintain the analog meter for pealing the tuning. I find it much easier to watch the meter bob up and
down than deal with digits changing. What can I say, I am old school.
I don’t understand why those thermocouples are so easily damaged.?
Nor do i know for sure why.? My guess is the resistor was pushed to its power dissipation
limits as the factory calibration procedure was to use a DC Current source which would
provide 1 AMP across the resistor when the resistor was at room temperature. With that
1 amp current the lab specified a voltage measurement of 19.6 milliVolts across the
resistor at room temp. Once the resistor warmed up and drove the meter to its cal
mark, the voltage drop across the resistor was suppose to be 20.0 milliVolts.
There must have been some variance in the thermocouples as there were two resistors
that were hand selected at the production floor in series with each lead of the thermocouple.
The values were selected so that when the resistor presented with 20 milliVolts across it,
that the Multiplier meter would indicate "1" on the meter scale. The provided information
was that those two resistors in series with the thermocouple were inside the sensor head.
The sensor head was sealed with glass.
Looking back at some notes from the conversation with the retired Boonton engineer,
the resistor was porcelain that was fired with a layer of platinum. Each resistor was
hand trimmed using an abrasive substance to reach the precise 20 milliOhms. The
reason provided for all of this effort was to mitigate the resistor's inductive effects
on Q measurements.
What I find interesting is that the inference is that the resistor will have 1 Amp of
current flowing through it when the Q Meter's Multiplier meter is set to "1".? Looking
at the schematic, the rf power source is the 5763 tube based oscillator. There is
a winding on the coil assembly which I take is to reduce the output impedance of
the tube to a low ohm value to drive the resistor. While the 1 amp current seems
outrageously high to me, I^2R still yields only 20 milliWatts. Talk about some
"outside the box thinking",
You may find this article on the Boonton model 280 Q Meter to be of interest. It is
the Boonton app note for the unit.
It was designed to measure Q between 210 MHz and 610 Mhz up to 25,000.
_._,_._,_
?
If I bought one I would send it to Keysight - assuming that they will still calibrate it, which I suspect that they will. I have a healthy scepticism of calibration labs.?
Based on my experience, if Keysight has continued the policy of former HP 7 Agilent,
they will refuse to service the box. In 1995 one of the five
HP-4342A's in the lab I worked pegged the meter out. We? contacted HP in Maryland
to arrange return for repair and calibration, but were told it was an old and obolete
product which they no longer supported. A few weeks later we encountered the same
issue with? an HP-8505A network analyzer. Very frustrating. Of course they were very
much ready to sell us new network analyzers.
Fortunately there are many metrology service labs willing to repair older equipment
so the more complex devices can still be repaired and calibrated.
?
Chuck
|
Hi:
The design using a thermocouple was done in ancient history when
vacuum tubes all had 4 pins.? They could easily be burned out and
were replaced on the next generation Q-meters.
The TS-617 is a functional replacement for the Boonton 160, but does
NOT use a thermocouple and instead uses a resistor divider.
David:? You might do a simulation of what a Z:Transform measurement
would look like for the coils you want to test.
The idea is to see if the VNA step size is small enough to get a
couple dozen points on the Smith Chart circle.? I'm guessing that,
depending on the VNA specs, may limit this method.
This is the method used in the HP E5100 Crystal Impedance Meter but
I don't remember the frequency step size.
--
Have Fun,
Brooke Clarke, N6GCE
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------
toggle quoted message
Show quoted text
If you have not already done so, you may want to read through the
Boonton 260 Q Meter manual.
It is a wealth of information and provides a lot of insight on
where errors creep into measurements.
The manual can be found at the following link:?
Boonton's approach was to use a 20 milliOhm precision resistor
with an attached thermocouple that
drove a panel meter. By measuring the power dissipation of the
resistor, they obtained a known
voltage drop across the resistor. The integral VTVM measured the
voltage across the tuned circuit
and the display meter was scaled in Q based on the results of the
ratio of the tuned circuit voltage
to the voltage across the precision resistor.
HP bought out Boonton and marketed the 260A for a few years before
presenting the HP4342 series
of Q Meters. I have not confirmed but was told that HP abandoned
use of the precision resistor in
the 4342A. I used the 4342A for years in the 80's through the
early 2000's. It is a tough box and in
my opinion, if you can buy one with unmolested innards, it is well
worth the cost of repair and calibration
in a metrology lab.
|
Hello everyone,
You may want to have a look at this article that I wrote in QEX, ten years ago:
Q Factor Measurements on L-C Circuits.
Jacques,? VE2AZX
|
Here is the Q page of W7ZOI
with his Q meter method and lots of theory.
??????????????????? Mikek
|
This site has a novel way to
Counter inductance of the 0.02Ω output resistor, but
he still only gets to 40MHz, But maybe you could have two
transformers, one for above 40MHz and one for below.
At bottom of page.
|
I also have Boonton 260A. I
had series of 5 coils that had Qs over 1000. I wanted to see
about coil spacing, On these 6" coils I found 10 to 12 turns per
inch got the highest Q using 660/43 Litz wire. Graph of coil Qs,
?I used a BNC T to tap into the RF drive and connected an RF
voltmeter to measure the drive, RF drive needs to be lowered
below the reading of the existing Multiply by meter. Then you
have a new multiplier times the Q meter reading. New multiplier
number depends on drive voltage.
?I found good agreement with the 3db method, but the 3db method
gets tricky at Qs over 1000!
You probably know but the 260a manual is here, good theory
section also.
??????????????????????? Mikek
?
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OOps again - I meant 74HC4059 (/10000 capable), not 74HC40102 (/100
capable). Also note that it is easy to force the counters to a known
starting state for each measurement with the Kb mode input and a small
amount of logic.
Stephen Menasian
|
On 8/4/2022 3:19 AM, Dr. David Kirkby,
Kirkby Microwave Ltd wrote:
Can anyone
think of a way of turning a signal generator to have an output
impedance of 1 milli ohm?
Like most engineering
decisions, it depends.? In this case my first though would be
negative feedback around an amp.? You can get almost
arbitrary reduction of output impedance as a tradeoff for other
parameters.? This is much more practical at much higher
frequencies than years past.
At frequencies where? negative feedback is not practical,
conventional transformers are not terribly likely to useful or
practical.? It may be that the kind of transformers used in RF
power amplifiers may be as they can be matching sub one ohm
impedances to 50 ohms.
Finally, filter structures can achieve wide impedance
transformations.? Of couirse these are subject the practical
limitations of components.? Since you are focusing on output
impedance you are likely to make different optimizations are so
find the impedance transformations you wish more achievable.
Oz (in DFW, Texas)
|
Dr. David Kirkby, Kirkby Microwave Ltd
John Kolb