Standard capacitors down to 1 fF
I see a General Radio 0.01 pF 0.03% capacitor on eBay today (image attached, as eBay links soon disappear).
These use 3 terminals, not 4. In the case of the 1 fF, 10 fF, 100 fF and 1 pF values, there are two capacitor plates with a grounded plate between them. The size of the hole in the plate determines the capacitance.
I wonder how one goes about determine the size of the hole? I'm interested if I could make something like this and put it on my Agilent 4284A and 4285A LCR meters. I have no idea what I would trust the mot - the LCR meter or my homemade capacitor. Both LCR meters are outside their calibration period, but both were calibrated within the last 5 years by Keysight, and have been in my possession since they were calibrated.
Dave
|
Re: Boonton Q Meter Thermocouple & Precision Resistor
On Sun, Aug 14, 2022 at 08:31 AM, Chuck Moore wrote:
The question was asked previously why the thermcouple heads
in the Boonton Q Meters were so fragile and prone to burnout
so easily.
<snip>
If you look at:
That's Brooke Clarke, who is a member of this list. <snip>
Back to the Q Meter.
The thermocouple is heated by a short length of what is reported
to be nichrome wire. The writer at prc68 reports the wire is 37
gauge or 0.0045" in diameter. The nichrome wire heater and the
thermocouple both are mounted on the bakelight disc inside the
sensor head. and the thermocouple bead is welded to the heater
wire.
In looking at a chart which showed various nichrome wire gauges
and the expected temperature of the wire when a specified current
flows through the wire, 37 gauge Nichrome A wire would reach 1600
degrees F for 1000 milliAmps flowing through the wire.
Looking at the chart found here:
you can see a fairly wide range of temperatures for currents varying
from 350 milliAmps (400 degrees) to 1290 milliAmps (2000 degrees F).
The reported melting point for Nichrome A wire is 2,552 degrees F. The
current to reach 2000 degrees is only 29% over the current reported to
be flowing in the precision resistor in the Q Meter.
Ah, so the sense wire gets very hot. I assume that means ambient temperature changes are no so significant, as it's so far above ambient. I thought I read in the 260-A manual that the RF signal generator only run at 50% of the power that could destroy the thermocouple, implying this would not happen like it did in the 160-A But maybe I got that wrong.
If you examine the
scale of Boonton 260's Multiply Meter which is monitoring the current
through the nichrome wire, the meter is marked with a red zone that
begins at about 5% of the meter scale above the meter scale's "Multiply
by 1" mark. It appears that the heater operates at a temperature that is
was approaching 63% of the wire's melting point.
Em, I like to design things with a bit more to spare than that!
Peter Olin, AI2V (reported to be a silent key) at one time provided repairs
and conversions of the 260 Q meter to include sensor head repairs. I also
remember that one conversion of the unit led to the vacuum tubes being
replaced with solid state active devices. From what I could determine most
conversions were driven by the lack of availability of the BR535 vacuum
tube (triode) used in the integral AC VTVM.? (I will repeat what I stated pre-
viously, the BR535 was a hand selected triode. A popular triode of the period
(I forget the industry part number for the tube) was purchased by Boonton
and each tube was tested for use in the Q Meter. Peter told me that culling
was dictated by an abrupt change in input impedance of the tube at 1 MHz.
Apparently there was a relatively frequent production error in manufacturing
the tube that caused the perturbation and Boonton's solution was to cull tubes
which presented with the undesired characteristic.
Another piece of information from my notes on the box is the resistors
R203 and R204 in the leads to the "Multiply by" meter are hand picked
at the time of installation of the thermocouple head. Apparently the
output voltage slope of the thermcouples varied and to compensate
for the delta between units, the resistor values were adjusted. Values
generally were between 30 ohm and 65 ohm. Equal value resistors
were used in each lead. The capacitors were in place to attenuate
RF that might couple into the sensitive "Multiply by" meter. The typical
0.01 uF value was chosen for service.
Many of the older units have a General Electric voltage stablilizer
block mounted on the floor of the box. In the last 20 years each one
I encountered either had failed or was in the process of failing. The
devices are enclosed in a stamped metal shell and filled with a 'GOO'
that makes a mess when the unit overheats. The GE boxes were
there to address line voltage fluctuations. Given the stench they
made when going up in smoke, I pulled the stabilizers out and use an
external UPS to provide well regulated AC power.
Please let me know if you notice any of the above info is in error and
also of any additions you might make.
Regards
Chuck WD4HXG
Thank you. Your comments certainly help understand why the things burn out so easily. How does one know if the thermocouple assembly is faulty? I ask this from the view of a person that has bought a supposedly working 160-A from eBay from a seller with a rather poor feedback. The attraction to the auction was the unit appears in good physical shape and that the shipping charges were less than $30 from the USA to the UK. I don't yet have the meter, but would like to know how to run some checks when it arrives. I do have a couple of Boonton Q standard inductors. One covers 50 kHz to 150 kHz and the other 150 kHz to 450 kHz. Dave
|
Re: AC Voltage Calibrator, home built
Great document!
I don't like the idea of taking a thermocouple from a working Q Meter however. An alternative would be taking one from a World War surplus RDF Ammeter.
Back in the '60's, we were calibrating differential voltmeters with AC 0.1% spec using an HP signal generator into a McIntosh audio amp into the secondary of an audio output transformer to generate high voltage, and measuring it with a Holt thermal transfer to compare with our Cohu 321 DC standard.
John
toggle quoted message
Show quoted text
On 8/14/2022 12:16 PM, Jacques Audet wrote: Hello all,
You may have a look at my document on:? Calibration Techniques for the Home Lab
I have had good results with a full wave rectifier using 0.1% resistors, as shown on page 25.
Using a thermocouple will provide even better accuracy, provided you use 6.5 digit DC voltmeters.? Starting at page 30.
That gives me a precise 1.000 VAC reference which allows verification of my multimeters.
A stable AC source driving an amplifier with? Kelvin Divider allows for checking at voltages up to 200VAC.
Jacques? VE2AZX
|
Re: Making a Q-meter / References etc
On Sun, 14 Aug 2022 at 19:33, Jacques Audet < Jacaudet@...> wrote: Thanks for the NPL paper.
My Q factor measurement technique is as simple as possible.
It only requires amplitude ratios to be measured.? No angle measurement
is required.
Both series and shunt modes connections are supported, as shown in my
Excel document.
The useful frequency range is below 1 GHz.
Of course results will be more precise with a 'professional' type VNA,
using two port full mismatch corrections.
The user may / should measure S21 at various attenuation levels and see
the effect on the computed Q factor.
This procedure could be automated too.
I have used MATBAB/Octane a but, but it wasn’t clear to me that the NPL code could read a Touchstone file.?
Regarding 1 pF capacitor accuracy, these may be measured in the series
mode with a VNA by measuring S21 and
computing the capacitance value.
That is okay in a test jig for small capacitors, but less suitable if trying to measure the capacitance between a wire from the source in a Q-meter and a wire from the detector.?
For some experiments at least, my intention was to use Banana sockets spaced 25.4 mm apart, which is what HP and Boonton used. That would allow comparisons with Q-standard coils like the attached. (It was sitting on a bench, connected to an HP 4284A LCR meter when the photograph was taken. I have turned the photograph through 180° so the writing is up the right way. It is not attached to the ceiling as it looks in the photograph). ???
Jacques? VE2AZX
G8WRB -- 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
|
Hello David,
No need to apologise, you did reply.
regards?? Ken g8beq
On 14/08/2022 21:43, Dr. David Kirkby,
Kirkby Microwave Ltd wrote:
toggle quoted message
Show quoted text
On Thu, 4 Aug 2022 at 10:13, Kenneth Greenough via
<g8beqglossop= [email protected]>
wrote:
Re' a Q meter.
This is only a thought idea, not tested hi.
Have a small enclosure with sockets on opposite sides.
each socket has a
single turn loop attached with sufficient distance between
the two loops
to allow the coil under test to be positioned between
them. one turn is fed
from your sig' gen' and the other feeds a scope or RF
meter.? A sufficient
level from the sig gen may require an amplifier. With the
coil to be tested
placed between the loops tune the sig gen for maximum
throughput, ie
resonance. Then tune the sig gen lower until the
throughput is 3dB
down, ie 0.71 reduction in voltage or 1/2 power. Repeat by
tuning the sig gen
higher than resonance for a similar drop in throughput.
the resonant
frequency divided by the bandwidth just ascertained is the
Q of the coil.
The coil being tested can, of course, have a capacitor in
parallel if wished.
73 Ken G8BEQ
?
Apologies for not replying earlier.
Yes, this is a known method, although it seems more common to
use a VNA now and measure S21 as that makes sweeping the
frequencies much easier.
Both inductive and capacitive coupling
can be done. That measures the loaded Q. I think I am
right in saying that the coupling factor at each end of the
DUT needs to be the same in order that it computes the unloaded
Q, which is what is required. See particularly section 3
of
A good practice guide from NPL does
this, but fits the transmission curve, not just a measurement
of 3 places.
Dave
|
On Thu, 4 Aug 2022 at 10:13, Kenneth Greenough via <g8beqglossop= [email protected]> wrote:
Re' a Q meter.
This is only a thought idea, not tested hi.
Have a small enclosure with sockets on opposite sides. each socket
has a
single turn loop attached with sufficient distance between the two
loops
to allow the coil under test to be positioned between them. one turn
is fed
from your sig' gen' and the other feeds a scope or RF meter.? A
sufficient
level from the sig gen may require an amplifier. With the coil to be
tested
placed between the loops tune the sig gen for maximum throughput, ie
resonance. Then tune the sig gen lower until the throughput is 3dB
down, ie 0.71 reduction in voltage or 1/2 power. Repeat by tuning
the sig gen
higher than resonance for a similar drop in throughput. the resonant
frequency divided by the bandwidth just ascertained is the Q of the
coil.
The coil being tested can, of course, have a capacitor in parallel
if wished.
73 Ken G8BEQ
? Apologies for not replying earlier. Yes, this is a known method, although it seems more common to use a VNA now and measure S21 as that makes sweeping the frequencies much easier.
Both inductive and capacitive coupling can be done. That measures the loaded Q. I think I am right in saying that the coupling factor at each end of the DUT needs to be the same in order that it computes the unloaded Q, which is what is required. See particularly section 3 of
A good practice guide from NPL does this, but fits the transmission curve, not just a measurement of 3 places.
Dave
|
I have the following:
?
HP 3575A gain-phase meter
HP K34-59991A phase comparator
Tracor 527A & 527E frequency difference meters
?
The 527’s are handy for fast convergence of a significantly off-frequency signal.? Then for fine adjustment both the HP meters are called into use.? The analog output of the 3575A can be fed into a PC for long-term analysis and is handy for setting the crossover point of quartz crystal based standards.
?
Greg
|
Re: AC Voltage Calibrator, home built
I haven't been following this thread too closely, so I apologize if this has already been discussed. That said, distortion in the source becomes increasingly important as one pursues ever greater accuracy. There has to be an error budget term that comprehends this error source.
The thermocouple is great at measuring true power independently of waveshape, but as soon as one tries to relate power to amplitude, the distortion issue rears its head.
Cheers
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
toggle quoted message
Show quoted text
On 8/14/2022 12:16, Jacques Audet wrote: Hello all,
You may have a look at my document on:? Calibration Techniques for the Home Lab
I have had good results with a full wave rectifier using 0.1% resistors, as shown on page 25.
Using a thermocouple will provide even better accuracy, provided you use 6.5 digit DC voltmeters.? Starting at page 30.
That gives me a precise 1.000 VAC reference which allows verification of my multimeters.
A stable AC source driving an amplifier with? Kelvin Divider allows for checking at voltages up to 200VAC.
Jacques? VE2AZX
|
Re: AC Voltage Calibrator, home built
Hello all,
You may have a look at my document on:? Calibration Techniques for the Home Lab
I have had good results with a full wave rectifier using 0.1% resistors, as shown on page 25.
Using a thermocouple will provide even better accuracy, provided you use 6.5 digit DC voltmeters.? Starting at page 30.
That gives me a precise 1.000 VAC reference which allows verification of my multimeters.
A stable AC source driving an amplifier with? Kelvin Divider allows for checking at voltages up to 200VAC.
Jacques? VE2AZX
|
Re: Making a Q-meter / References etc
Thanks for the NPL paper.
My Q factor measurement technique is as simple as possible.
It only requires amplitude ratios to be measured.? No angle measurement is required.
Both series and shunt modes connections are supported, as shown in my Excel document.
The useful frequency range is below 1 GHz.
Of course results will be more precise with a 'professional' type VNA, using two port full mismatch corrections.
The user may / should measure S21 at various attenuation levels and see the effect on the computed Q factor.
This procedure could be automated too.
Regarding 1 pF capacitor accuracy, these may be measured in the series mode with a VNA by measuring S21 and
computing the capacitance value.
Jacques? VE2AZX
|
Boonton Q Meter Thermocouple & Precision Resistor
The question was asked previously why the thermcouple heads
in the Boonton Q Meters were so fragile and prone to burnout
so easily. After looking around on the web, reviewing some old
notes in my library and speaking to a few retired techs and engineers,
it appears some answers may be available.
If you look at:
you will see more info on the Q Meter sensor head. The writer's
observation clarified a couple of misconceptions I had about the
sensor head. One was the mounting of the thermocouple. For
decades my assumption was the thermocouple was mounted
to the 20 milliOhm precision disc resistor. In reality it is mounted
on a bakelight disc shaped board. The writer at prc68.com
measured the wire diameter and reports it to be 46 gauge. That
works out to a wire diameter of just 0.0016" for the thermocouple.
Making the spot weld must have been fun in the 50's with that
small wire. It explains a lot about the sensitivity to shock.
(As an aside a PMEL tech told me that the HP/Agilent RF Power
Meters use a similar thermocouple with fine wire. As they were
smaller and more prone to shocked, the failures were and still
are frequent.)
Back to the Q Meter.
The thermocouple is heated by a short length of what is reported
to be nichrome wire. The writer at prc68 reports the wire is 37
gauge or 0.0045" in diameter. The nichrome wire heater and the
thermocouple both are mounted on the bakelight disc inside the
sensor head. and the thermocouple bead is welded to the heater
wire.
In looking at a chart which showed various nichrome wire gauges
and the expected temperature of the wire when a specified current
flows through the wire, 37 gauge Nichrome A wire would reach 1600
degrees F for 1000 milliAmps flowing through the wire.
Looking at the chart found here:
you can see a fairly wide range of temperatures for currents varying
from 350 milliAmps (400 degrees) to 1290 milliAmps (2000 degrees F).
The reported melting point for Nichrome A wire is 2,552 degrees F. The
current to reach 2000 degrees is only 29% over the current reported to
be flowing in the precision resistor in the Q Meter. If you examine the
scale of Boonton 260's Multiply Meter which is monitoring the current
through the nichrome wire, the meter is marked with a red zone that
begins at about 5% of the meter scale above the meter scale's "Multiply
by 1" mark. It appears that the heater operates at a temperature that is
was approaching 63% of the wire's melting point.
The "Multiply by 1" value on the meter scale appears at an estimated
80% position (1000 milliAmps) of full scale reading. If the meter? needle
position and scale is modestly linear, that suggests full scale reading of
the meter will be 1250 milliAmps. On my Boontoon 260, the "Multiply
by" factor control not only allows one to reach full scale, but? if careless
the meter can be pegged out. That may explain why so many meters blew
the heater wire and destroyed the thermocouple. If you look at the photo
(Figure 2) of the thermocouple sensor head at:
you can see the char marks on the Bakelite terminal board of an exemplar
thermocouple head.
Peter Olin, AI2V (reported to be a silent key) at one time provided repairs
and conversions of the 260 Q meter to include sensor head repairs. I also
remember that one conversion of the unit led to the vacuum tubes being
replaced with solid state active devices. From what I could determine most
conversions were driven by the lack of availability of the BR535 vacuum
tube (triode) used in the integral AC VTVM.? (I will repeat what I stated pre-
viously, the BR535 was a hand selected triode. A popular triode of the period
(I forget the industry part number for the tube) was purchased by Boonton
and each tube was tested for use in the Q Meter. Peter told me that culling
was dictated by an abrupt change in input impedance of the tube at 1 MHz.
Apparently there was a relatively frequent production error in manufacturing
the tube that caused the perturbation and Boonton's solution was to cull tubes
which presented with the undesired characteristic.
Another piece of information from my notes on the box is the resistors
R203 and R204 in the leads to the "Multiply by" meter are hand picked
at the time of installation of the thermocouple head. Apparently the
output voltage slope of the thermcouples varied and to compensate
for the delta between units, the resistor values were adjusted. Values
generally were between 30 ohm and 65 ohm. Equal value resistors
were used in each lead. The capacitors were in place to attenuate
RF that might couple into the sensitive "Multiply by" meter. The typical
0.01 uF value was chosen for service.
Many of the older units have a General Electric voltage stablilizer
block mounted on the floor of the box. In the last 20 years each one
I encountered either had failed or was in the process of failing. The
devices are enclosed in a stamped metal shell and filled with a 'GOO'
that makes a mess when the unit overheats. The GE boxes were
there to address line voltage fluctuations. Given the stench they
made when going up in smoke, I pulled the stabilizers out and use an
external UPS to provide well regulated AC power.
Please let me know if you notice any of the above info is in error and
also of any additions you might make.
Regards
Chuck WD4HXG
|
Here are a couple more pages with info about ways to measure Q.? Mikek
http://w7zoi.net/twofaces.pdf
https://docplayer.net/39575747-Experiments-with-coils-and-q-measurement.html
Or the same on the Wayback machine.
|
Re: AC Voltage Calibrator, home built
There is always the venerable HP745A. ? (up to110KHz)
A Rube-Goldberg, if there ever was one.
Quite accurate for an instrument 50+ years old.
I have two, different vintages, and both quite close to each other,still.
Watch the +1,000 volt settings, tho.? One handed operation.
Don N5CID
===========================================
On 8/13/2022 4:42 PM, Dr. David Kirkby,
Kirkby Microwave Ltd wrote:
toggle quoted message
Show quoted text
On Mon, 8 Aug 2022 at 10:15, tgerbic < tgerbic@...>
wrote:
I would like to get some
thoughts from others about how they do AC calibration
outside of a rheostat/isolation transformer on a 50/60Hz
power line, or a sinewave generator for low voltages.
Another possibility below 1 MHz or so,
would be a light bulb and light meter. Apply AC to the
lightbulb and it will glow. The light meter indicates the
illumination level. Then apply DC to the light bulb to produce
the same level of illumination as the AC did. That allows you
to calculate the RMS voltage of the AC source.
Problems would arise when the
inductance of the bulb becomes significant, but I doubt that
would be an issue below at least 1 MHz.
I'm pretty sure that above would work,
but I don't know what uncertainty you could achieve.
Dave
|
Re: AC Voltage Calibrator, home built
On Mon, 8 Aug 2022 at 10:15, tgerbic < tgerbic@...> wrote: I would like to get some thoughts from others about how they do AC calibration outside of a rheostat/isolation transformer on a 50/60Hz power line, or a sinewave generator for low voltages.
Another possibility below 1 MHz or so, would be a light bulb and light meter. Apply AC to the lightbulb and it will glow. The light meter indicates the illumination level. Then apply DC to the light bulb to produce the same level of illumination as the AC did. That allows you to calculate the RMS voltage of the AC source.
Problems would arise when the inductance of the bulb becomes significant, but I doubt that would be an issue below at least 1 MHz.
I'm pretty sure that above would work, but I don't know what uncertainty you could achieve.
Dave
|
Re: Making a Q-meter / References etc
On Sat, 13 Aug 2022 at 15:37, Jacques Audet < Jacaudet@...> wrote: Hello All,
Measuring the Q factor may be easily done with a VNA or a nanoVNA, for
instance.
The measurement set-up cannot be simpler:
Connect the L and C in series and in shunt across a transmission line
and measure the S21 parameter
at the frequency(ies) of interest.? The reference capacitor is used to
establish resonance.
This should be a low loss capacitor (a vacuum capacitor perhaps).
Measure the loss (S21) at the resonant frequency, and below and above
the resonant frequency.
There's a 105 page paper from Andrew Gregory at NPL on this topic.
along with some MATLAB/Octave and Python code. That fits multiple points on the transmission curve - not just 3. One significant difference from a simple S21 measurement with a VNA is that there is a lot (40 dB) attenuation added in series with the inductor/capacitor.
> Jacques,? VE2AZX
If I recall correctly, I see something similar from yourself in your QEX paper, where capacitors of around 1 pF were used. When I went looking for more information on this, it seems the coupling needs to be identical on both sides of the coil. Whilst that is easy to achieve if the capacitors are 1000 pF, it is not so easy when the capacitors are very small.
Dave, G8WRB.
|
Re: Making a Q-meter / References etc
Hello All,
Measuring the Q factor may be easily done with a VNA or a nanoVNA, for instance.
The measurement set-up cannot be simpler:
Connect the L and C in series and in shunt across a transmission line and measure the S21 parameter
at the frequency(ies) of interest.? The reference capacitor is used to establish resonance.
This should be a low loss capacitor (a vacuum capacitor perhaps).
Measure the loss (S21) at the resonant frequency, and below and above the resonant frequency.
Enter these points in the Excel sheet that I designed.?? It reports the component values ESR and Q...
See:?
For crystal Q measurements:
Calculate the Loaded and Unloaded Q Factor of a Resonator:
Q Factor Measurements with an SWR Meter:
??????? Link to spreadsheet:
Jacques,? VE2AZX
|
Hello,
the quote from Wikipedia is correct in the theory, wrong in the practice.
WebAssembly itself is but an ISA which is implemented in the browser. The magic takes place a logical layer above, where frameworks such as Uno Framework can take a, say .net app, and transform it into a WebAssembly page. Of course, this transform also includes the DOM access wrapper which renders the, say, XAML in the browser.
I am currently stuck in Vienna helping my ex wife. When I come back next week, I can set up on my workstation a demo app for you.
Tam
Okay. I set up what I had in mind at
You can see the basic structure * Chose the instrument (HP 4284A or 8285A) * Set cable length, measurement type, temperature.
The basic plan was to compute the uncertainty. But let's take discussions about WebAssembly, JavaScript, DOM etc to private email, as they are completely off topic for the group.
Dave
|
Hello, the quote from Wikipedia is correct in the theory, wrong in the practice. WebAssembly itself is but an ISA which is implemented in the browser. The magic takes place a logical layer above, where frameworks such as Uno Framework can take a, say .net app, and transform it into a WebAssembly page. Of course, this transform also includes the DOM access wrapper which renders the, say, XAML in the browser. I am currently stuck in Vienna helping my ex wife. When I come back next week, I can set up on my workstation a demo app for you. Tam On August 12, 2022 11:26:32 PM GMT+02:00, "Dr. David Kirkby, Kirkby Microwave Ltd" <drkirkby@...> wrote:
On Fri, 12 Aug 2022 at 17:29, Tam Hanna < tamhan@...> wrote:
Hi,
do NOT use JavaScript for something so complex.
WebAssembly allows you to use a real programming language. You
can, for example, use C# and the Uno Framework, and then get a
WebAssembly output web page which can run in ANY web browser, even
on Linux and Mac OS.
Tam
It's not so complex - just tedious. I attach the specifications from the 4285A LCR meter manual. On page 8 it describes how to work out the accuracy. On page 9 you see equations for A1, A2, A3 ....A16. But only one of those is relevant. To determine what one is applicable you have to look at the graphs on pages 11 and 12. Then there's a cable length factor Ac, which depends on the length of the cables and frequency. There are other factors N1 and N2 which depend on frequency.? Another factor depends on temperature. Once you know all these factors you can work out accuracy of inductance, capacitance resistance etc. Then to work out Q you have to apply more formulas, and factors which depend on the indicated Q.
It basically becomes a big tedious mess. I would like a web page that does those calculations for the 4284A and 4285A.
Keysaid said they would consider having a spreadsheet for the newer meter. If they did that, I could probably hack it for my older meters.
I thought Javascript would be the way to create a webpage, although I admit my knowledge of web design does not extend beyond HTML and a bit of CSS. You mentioned not to use that, but use WebAssembly
According to Wikipedia at least
in the limitations section, the first item mentioned is
"
In general, WebAssembly does not allow direct interaction with the . All interaction must flow through JavaScript interop."
So it seems I would need JavaScript anyway. I might as well do the rest in JavaScript, as I don't think the problem is sufficiently complicated that I would really warrant using a lange and toolset I dont know.
Dave
With best regards Tam HANNA -- Enjoy electronics, 3D printing and cigars? Join more than 21000 followers on my Instagram at
|
Re: "Electric field strength" measurements?
Unfortunately, in the world of EMC, where field strength measurements are our daily business, this antenna is not known for its accuracy. Indeed, its resonance frequency band is fuzzy and therefore wide inducing a very low accurate gain.?
See an excellent commercial realization of this antenna with the corresponding plots here :
http://schwarzbeck.de/Datenblatt/ksga2450.pdf
Therefore it is much more usual to use half-wave resonant dipoles as already indicated by Dr Kirkby. Of course any other calibrated antenna can also be used.
But field strength measurements have the distinction of having one of the highest inaccuracies recognized by the world of laboratory metrology since when we claim to have a measurement uncertainty of less than 3 dB, we are usually questioned by the auditors of accreditation bodies as to whether we are really being honest. In general, 4 dB of measurement uncertainty is accepted by all international standards.
?
|
Re: AC Voltage Calibrator, home built
Hi Guys, ? One method of AC voltage measurement that is easy to build and calibrate is the shunt diode detector. With suitable components and layout, a frequency response up to the low GHz, flat to ±1dB is possible. The low frequency response is determined by the input capacitor’s value.? Calibration is achieved using a an audio oscillator, amplifier and a true RMS DMM, with an accuracy of ±0.5% to calibrate the AC/DC transfer curve. If the detector’s designed low frequency response doesn’t extend into the audio region. temporarily add a larger capacitor to extend the low frequency response into the audio region. ? I have built several germanium diodes probes using diodes similar to the OA81. These have a PIV of 70V, giving a max RMS input of 24.5V, which equates to 12W into 50Ω (40.8dBm). This would give repeatable readings down to around -10dBm (0.3mV). For higher voltages an attenuator would be required. For RF work, this could be implemented as part of a test load using a tubular 50Ω resistor. The diode is connected to a point, say 10% up from the cold end, which gives several advantages. It reduces the diode detector’s loading of the signal, improves the return loss and? increases the power capability up to 1.2Kw. ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Patricio A. Greco via groups.io
Sent: Saturday, 13 August 2022 03:50
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] AC Voltage Calibrator, home built? I’ve an HP434A working perfectly. Its a great transfer standard ? Ing. Patricio A. Greco
Taller Aeronáutico de Reparación 1B-349
Organización de Mantenimiento?Aeronáutico de la Defensa OMAD-001
Laboratorio de Calibración ISO 17025?AREA: RF/MW?
Gral. Martín Rodríguez 2159
San Miguel (1663)
Buenos Aires
T: +5411-4455-2557
F: +5411-4032-0072
? While for RF, the information on this site might be relevant. ?
?
|
Dr. David Kirkby, Kirkby Microwave Ltd
John Kolb
