Re: 2 GHz spectrum analyzer mostly build out of eBay modules
Hi Erik
Your design is really good. At the cost level it is still reasonable considering the announced possibilities DC-> 1.8gHz For the software, did you start from the Ashar code for the Specan / Sweeperino or did you write it entirely. Can you, when you have finished making available the .hex or possibly the .ino?
Thank you in advance for your answers and congratulations for this achievement. Photos can be?
73 QRO Gilles - F1BFU / Fr
Le?jeu. 3 janv. 2019 ¨¤?14:59, < erik@...> a ¨¦crit?: [Edited Message Follows]
This is the high level diagram
Regular dual conversion architecture with two mixers with first IF for image suppression at IF1 and second IF for resolution bandwith at IF2 and log detector for conversion to dBm
I used IF1=2.5GHz and IF2=10.7MHz with the ADF4351 this gives me DC to 1.8GHz input range
Attenuator is either a module for the right frequencies of fixed attenuator as required
The low pass filters eliminates anything above IF1-IF2, I used a 1.8GHz lowpass filter module from ebay
M1 and M2 are mixer modules with one port for DC to IF1 frequency and two ports with IF1 till 2 times IF1 frequency. I used SIM-83+ modules from ebay, a bit overspec as these go to 8GHz
LO1 sweeps and goes from IF1 to max two times IF1. I used ADF4351 module from ebay
IF1 filter has bandwith of less then two times IF2. I used second hand cavity filter from ebay (difficult to find) but you can build your own interdigital filter
LO2 is fixed at IF1-IF2. I used ADF4351 module from ebay
IF2 filter has bandwith for required resolution, 300kHz or 15 kHz or switchable. I build myself but there are 10.7MHz filter modules with bandwith of 15kHz available on ebay
The amplifier compensates for the loss in the mixers. I used 20dB low noise amplifier module from ebay
The log detector converts IF2 into measurement signal. I build myself with AD603 and AD8307 but there are AD8307 modules on ebay
The ADC (AD1) is an analogue input port of a arduino.
For the arduino you best use a zero or due as these are 3.3v just like the ADF4351 and attenuator modules
If you need max 150MHz you can use a single SI5351 module for both LO1 and Lo2 and AD831 active mixer modules as mixers so you do not need the 20dB amplifier module. 150MHz IF1 filters are hard to find on ebay. I used 110MHz SAW filters and put them in a small enclosure with SMA connectors.
Everything connects together with SMA pigtails from ebay.
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Re: 2 GHz spectrum analyzer mostly build out of eBay modules
This is the high level diagram  Regular dual conversion architecture with two mixers with first IF for image suppression at IF1 and second IF for resolution bandwith at IF2 and log detector for conversion to dBm I used IF1=2.5GHz and IF2=10.7MHz with the ADF4351 this gives me DC to 1.8GHz input range Attenuator is either a module for the right frequencies of fixed attenuator as required The low pass filters eliminates anything above IF1-IF2, I used a 1.8GHz lowpass filter module from ebay M1 and M2 are mixer modules with one port for DC to IF1 frequency and two ports with IF1 till 2 times IF1 frequency. I used SIM-83+ modules from ebay, a bit overspec as these go to 8GHz LO1 sweeps and goes from IF1 to max two times IF1. I used ADF4351 module from ebay IF1 filter has bandwith of less then two times IF2. I used second hand cavity filter from ebay (difficult to find) but you can build your own interdigital filter LO2 is fixed at IF1-IF2. I used ADF4351 module from ebay IF2 filter has bandwith for required resolution, 300kHz or 15 kHz or switchable. I build myself but there are 10.7MHz filter modules with bandwith of 15kHz available on ebay The amplifier compensates for the loss in the mixers. I used 20dB low noise amplifier module from ebay The log detector converts IF2 into measurement signal. I build myself with AD603 and AD8307 but there are AD8307 modules on ebay The ADC (AD1) is an analogue input port of a arduino. For the arduino you best use a zero or due as these are 3.3v just like the ADF4351 and attenuator modules If you need max 150MHz you can use a single SI5351 module for both LO1 and Lo2 and AD831 active mixer modules as mixers so you do not need the 20dB amplifier module. 150MHz IF1 filters are hard to find on ebay. I used 110MHz SAW filters and put them in a small enclosure with SMA connectors. Everything connects together with SMA pigtails from ebay.
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Re: 2 GHz spectrum analyzer mostly build out of eBay modules
On Sat, Dec 15, 2018 at 07:58 AM, <erik@...> wrote:
I would also be interested in seeing what you have.? I am working on something similar only going up to 250 MHz.? It is using 31 MHz saw filters for first IF and second IF a t 10.7 Mhz.? I plan on using AD831 mixer modules and a si5351 with high pass filters for the first and second LO frequencies.? Will probably have 4 10.7 Mhz if band widths using available filters.? Will keep updates on my blog.
? -- DuWayne,? KV4QB
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Re: 2 GHz spectrum analyzer mostly build out of eBay modules
I second the thought.? Very impressive.? Understand there are some bugs but, publishing what you have will encourage others to give it a go.? Maybe even me!
Gene N2IJF
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Impressive! ?Any thoughts on publishing your circuit and methods of construction?
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Re: 2 GHz spectrum analyzer mostly build out of eBay modules
Impressive! ?Any thoughts on publishing your circuit and methods of construction?
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2 GHz spectrum analyzer mostly build out of eBay modules
Hi, Just wanted to share success in getting the first scan of my own build 2GHz spectrum analyzer build almost completely from readily available modules from eBay. Total cost is less then $200. Here is the first scan of a 200MHz signal coming from a SI5351. The signals at 400, 800, 1200 and 1600 MHz are difficult to see on the black grid lines. I'll need to improve this  The SW I made (see picture) is still a bit rough, the signal at 1.84GHz is an alias the 2.0GHz low pass filter did not yet arrive. The actual resolution BW is 300kHz and the actual span is 2GHz All the modules are lying on a table, no decent shielding yet. Lots of unwanted signals below 400MHz Configuration: input->switchable attenuator(0-32dB)->mixer (LO 2.5-4.4GHZ) -> cavity filter(2.5GHz) ->IF amplifier->mixer(LO 2.489.3GHz)->resolution filter (10.7MHz, 15/300KHz BW)->AD8307 log detector->Arduino->Serial->PC Main components: switchable attenuator 0-32dB 2 * SIM-83+ 8Ghz mixer module 2 * ADF4351 35MHz - 4.4GHz generator module as LO Broadband amplifier 0-6GHz 20dB (to compensate for the 2*7dB mixer loss) Cavity bandpass filter somewhere between 2GHz and 2.5GHz with steep cutoff Bandpass filter at 10.7 MHz 300kHz/15kHz switchable BW (this I build myself from ebay cristal and ceramic filters and some other small components ) AD8307 Log detector module Arduino uno Set of SMA pigtails In the coming weeks I will add an additional 110Mhz IF stage to reduce images and spurs (although there are not many and I have SW spur elimination) and the input low pass filter to reduce aliasing The SW can be configured for 2 or 3 IF and any combination of IF frequencies. I did tests with 110MHz and 500MHz as first IF before receiving the cavity filter. A somewhat cheaper build uses 2Ghz mixers (ADE-11X) and a 1090MHz ADS bandfilter instead of the cavity filter. This will give you a 1GHz spectrum analyzer and due to the small BW of the ADS filter you will not need a 3rd IF I hope this inspires some creative building!
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Doug, kinda depends on what you use it for I guess.?
?
I spent some time pondering this a couple months ago.? The old school HP350s used 3 to 7 watt resistors, the 355's look smaller, didn't see wattage spec in the ops manual, but the manual cautions not to exceed half a watt, and the QRPGuys attenuator board uses 3 watters, and says they think that will handle 10 watts at 50 percent duty cycle.
??
?I ended up buying a cheap HP355 (40 bucks) because of its 0 to 1 gig rating, but built a QRP guys board to "take the heat" in the first few decades of attenuation if it became necessary.? I modified the QRP Guys board for the last few positions, with 1/4 watters for higher attenuation, and probably because of my technique, the over 100 MHz frequency dependent results don't look as good as the QRP guys originals. go figure.
?
Not homebrew, but at some point, if it works better for less bucks, I had to draw the line :)
?
If you find a good cheap source of 3 watters good for 10, 20 and 30 db pads, please post it.
?
Cheers,? Scott ka9p
?
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-----Original Message-----
From: Doug W <dougwilner@...>
To: HBTE < [email protected]>
Sent: Fri, Dec 7, 2018 9:38 am
Subject: Re: [HBTE] Step Attenuators
Many designs I see for QRP step attenuators are using 1/4w resistors.? What am I missing?? Unless you plan on a duty cycle measured in seconds aren't you just making firecrackers?? I am planning on building one soon inspired by Arv's dead bugish design and keep looking at the mountain of 1/4 watters in my junk box wondering if I really should be looking at 1w or even 3w resistors.
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They are talking about attenuators for use between a signal generator and the radio for receive alignment where the signal is only a few micro-volts. Not for transmit.
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Many designs I see for QRP step attenuators are using 1/4w resistors.? What am I missing?? Unless you plan on a duty cycle measured in seconds aren't you just making firecrackers?? I am planning on building one soon inspired by Arv's dead bugish design and keep looking at the mountain of 1/4 watters in my junk box wondering if I really should be looking at 1w or even 3w resistors.
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ARV,
?I fear this design described is? a "component maxima"? !!!
A component tester could of a simplified type. I believe that more complex a design more the non-reliability.
regards
sarma
?vu3zmv
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Hi Arv, William
I mounted a component tester kit purchased from Ali for $ 14 and has many features. It is based on the library AVR Markus. Attached is a paper by Karl-Heinz Kubbeler "TransistorTester with AVR microcontroller and a little more Version 1.13k "which is very interresting. To see on the link?.
73 QRO Gilles - F1BFU /FR
Gilles
That post was a direct result of this morning's conversation with Hans (QRP-Labs).?
He has implemented some of the features, but not all.? We discussed methods and
other possible testing approaches.? That conversation was relative to the QSX
transceiver and what it might include.?
Use of a two-line display is limited but if a USB link to an attached PC the display
capability can be increased significantly.? Of course there are other small display
technologies that can be employed as well.?
Computer based testing can be simple or complex.? Faster processors allow more
testing in near real-time, but a lot can still be accomplished with the AVR/Arduino
boards.? Faster processors also allow some DSP-like signal analysis.
Arv _._
Good evening Arv
Hans (QRPLabs) did this with the QCX which includes his own test functions. - Built-in test signal generator and alignment tools to complete simple set-up adjustments
- Built-in test equipment: voltmeter, RF power meter, frequency counter, signal generator
With the use of the Teensy 3.6 (Jack & Al W8TEE) or STM32 Nucleo microcontrollers, we have enough memory and ports to perform all these settings and tests embedded in a transceiver.
73 QRO Gilles - F1BFU /FR
This project on Instructables shows how to build your own "Component Tester".
While it is complete in its own right, it could also be the basis for even more advanced
equipment.
Some of the ideas could possibly be incorporated into Arduino/Raduino controlled
transceivers as built-in test functions.
Arv? K7HKL _._
--
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I¡¯ve tried to convince Jack and Al these features would be invaluable in their new JackAl board for the uBITx... however I don¡¯t thing it will be released with any of these features. ?That aside there is plenty of space to easily add them.?
Dr.?William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch ¨C K9ZC Staunton, Illinois ? Owner ¨C Operator Villa Grand Piton - J68HZ Soufriere, St. Lucia W.I. Rent it:
email:??bill@... ?
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On Dec 4, 2018, at 7:26 PM, Arv Evans < arvid.evans@...> wrote: Gilles
That post was a direct result of this morning's conversation with Hans (QRP-Labs).?
He has implemented some of the features, but not all.? We discussed methods and
other possible testing approaches.? That conversation was relative to the QSX
transceiver and what it might include.?
Use of a two-line display is limited but if a USB link to an attached PC the display
capability can be increased significantly.? Of course there are other small display
technologies that can be employed as well.?
Computer based testing can be simple or complex.? Faster processors allow more
testing in near real-time, but a lot can still be accomplished with the AVR/Arduino
boards.? Faster processors also allow some DSP-like signal analysis.
Arv _._
Good evening Arv
Hans (QRPLabs) did this with the QCX which includes his own test functions. - Built-in test signal generator and alignment tools to complete simple set-up adjustments
- Built-in test equipment: voltmeter, RF power meter, frequency counter, signal generator
With the use of the Teensy 3.6 (Jack & Al W8TEE) or STM32 Nucleo microcontrollers, we have enough memory and ports to perform all these settings and tests embedded in a transceiver.
73 QRO Gilles - F1BFU /FR
This project on Instructables shows how to build your own "Component Tester".
While it is complete in its own right, it could also be the basis for even more advanced
equipment.
Some of the ideas could possibly be incorporated into Arduino/Raduino controlled
transceivers as built-in test functions.
Arv? K7HKL _._
--
|
Gilles
That post was a direct result of this morning's conversation with Hans (QRP-Labs).?
He has implemented some of the features, but not all.? We discussed methods and
other possible testing approaches.? That conversation was relative to the QSX
transceiver and what it might include.?
Use of a two-line display is limited but if a USB link to an attached PC the display
capability can be increased significantly.? Of course there are other small display
technologies that can be employed as well.?
Computer based testing can be simple or complex.? Faster processors allow more
testing in near real-time, but a lot can still be accomplished with the AVR/Arduino
boards.? Faster processors also allow some DSP-like signal analysis.
Arv _._
Good evening Arv
Hans (QRPLabs) did this with the QCX which includes his own test functions. - Built-in test signal generator and alignment tools to complete simple set-up adjustments
- Built-in test equipment: voltmeter, RF power meter, frequency counter, signal generator
With the use of the Teensy 3.6 (Jack & Al W8TEE) or STM32 Nucleo microcontrollers, we have enough memory and ports to perform all these settings and tests embedded in a transceiver.
73 QRO Gilles - F1BFU /FR
This project on Instructables shows how to build your own "Component Tester".
While it is complete in its own right, it could also be the basis for even more advanced
equipment.
Some of the ideas could possibly be incorporated into Arduino/Raduino controlled
transceivers as built-in test functions.
Arv? K7HKL _._
--
|
Good evening Arv
Hans (QRPLabs) did this with the QCX which includes his own test functions. - Built-in test signal generator and alignment tools to complete simple set-up adjustments
- Built-in test equipment: voltmeter, RF power meter, frequency counter, signal generator
With the use of the Teensy 3.6 (Jack & Al W8TEE) or STM32 Nucleo microcontrollers, we have enough memory and ports to perform all these settings and tests embedded in a transceiver.
73 QRO Gilles - F1BFU /FR
This project on Instructables shows how to build your own "Component Tester".
While it is complete in its own right, it could also be the basis for even more advanced
equipment.
Some of the ideas could possibly be incorporated into Arduino/Raduino controlled
transceivers as built-in test functions.
Arv? K7HKL _._
|
This project on Instructables shows how to build your own "Component Tester".
While it is complete in its own right, it could also be the basis for even more advanced
equipment.
Some of the ideas could possibly be incorporated into Arduino/Raduino controlled
transceivers as built-in test functions.
Arv? K7HKL _._
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Too narrow. His SNA would be a choice.?
I bought a RF-Explorer plus from seeed studio. Works well but not homebrew.?
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Re: Resolution, accuracy, error and digital displays
For the Arduino:
The a/d is 10 bits.? So max value is 1023 and min value is noise likely 2-4.
So the general resolution is 3 digits (999) and internal accuracy for that is fair.
So for three digits your display resolution and accuracy for about +-1 count (LSD).?
Depending on scale that is best case.
Now that does not allow for range setting resistors so that usually 1%.
Also for the dummy load the diode detector.? For power inputs over about 50mW
the diode is linear along with a ,2 to .5V offset for the threshold of the diode used.
For lower than 50mW input especially down near 1mW or less the accuracy is
really bad as the diode is in the square law region.? Its possible to calibrate for
powers down to about -40dbm (1/10000th of a milliwatt) of course each diode
mount is unique and calibration is required.? It is also a non-linear calibration.?
For better accuracy diode detectors using active bias and offset help.? For
powers less than that any of the IC log detectors (8703 and others) are really
the only way to get any accuracy from the detector portion.? ?Still for accuracy
calibration is required.
Typical power meters (BIRD and others ) 5% is typical at full scale for analog or
digital read outs.? At the low end of the scale it may be worse, possibly greatly.
The ability to measure, and display in digital instruments is limited by the A/D resolution
(number of bits, more is better, resolution), the monotonically of the A/D (resolution
accuracy), And then the number of displayed digits (to the max of the A/d resolution).?
None of that can improve on inputs that are un-calibrated but it can allow for a
calibration process to achieve improved accuracy.
In general, when I used a slide rule answers were typically 3-4 places resolution
and accurate to that.? Using a calculator allowed more digits but in reality with 1%
resistors and 5% caps 3 digits are about it.? Computers and sims allow for answers
typically to 6 places if not more, try to buy a 15122 ohm resistor!? ?Back in the day
most voltage reading for testing were in the range of better than 20% and 10% was
more than enough unless specified.? For power at 10W +-1W in hard to detect at
more than a small distance.? For greater distances the difference between 5 and
10W barely registers on the meter if at all.
With all that often good enough, we have power, is more than enough.
Allison
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Re: Resolution, accuracy, error and digital displays
Hi Michael,
All of those 'errors' are really the tolerance ranges of the various part. Worst case is that all of the parts are at one extreme limit and all of them modify the 'error' in the same direction. We call that a tolerance stack or error stack if you wish. In reality some of those 'errors' are going to cancel or partially cancel other errors and that is likely to be at random and affected by variables beyond our control. Temp variations, atmospheric variations (where applicable) and various other random "noise". To be useful the digits 3, 4, 8, n are only useful if the accuracy of the system is at least an order of magnitude greater than the resolution. There is that last digit flickering. So we leave it off and are allowed to sleep at night :)
Could it be possible that a computer program could exist? Golly. That's frightening <evil grin>. That looks like the same kind of error where we mix different units in our calculations. Measurements in millimeters and cutting in inches. Been there - done that - shrug.
If we are working on our mixer then milliwatts might be the most significant digits. Checking out a receiver front end it might be microwatts or picowatts in the most significant positions. The question of how many digits are needed is still relevant. Sometimes its a personal preference. Some men prefer blondes. Others like brunettes.
73,
Bill KU8H
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On 11/05/2018 07:34 PM, Michael Maiorana wrote: Into the deep end indeed. Of course there is likely no practical need to
know our output power down to the milliwatt. No doubt that the software
can be configured to display as many significant figures as we'd like.
The question is, at least in this particular case, how many should we be
displaying? Since we talk about test equipment here I thought it would
be a worthwhile exercise.
I got home from work today and read the article, then got the extras
from the arrl "in-depth" website. I'm extra confused now since I shyly
think that there is a bug. I'll get to that later.
I'm going to start with using 4 significant figures in the measurements.
Let's say we're only looking at a pure sine wave, which I think is a
reasonable abstraction. We turn up our ultra-accurate QRP rig and put
exactly 1 watt (30 dBm) into the 50 ohm dummy load. That should be 7.071
V rms or 9.998 V peak. The diode / capacitor detector circuit should
read peak voltage. From there the voltage is reduced to allow more range
in the 0-5V arduino input, so a voltage divider divides by 29. So the
voltage at the ADC would be 0.3448 V. Each bit in the arduino ADC is
4.883 mV per bit. That math gives 70.60, but it is binary so round to
71? The code averages 30 readings to smooth the reading. It then squares
the ADC reading and divides by the load resistance, then multiplies by a
"Calibration Offset" of 0.008704. The grand total is 877.5 milliwatts.
Since that "Calibration Offset" value is meant to be used for
calibration, in this example we'll use 0.009919 since that makes our
numbers work. 71 squared, divided by 50, time 0.009919 is 1.0000.
The issue I started with is possible error, and the displayed 4 digit
value in watts. What are the possible errors? The diode drop. The
tolerance of the resistors in the voltage divider network. The
temperature coefficient of the load resistors. The linearity of the
arduino ADC. Accuracy of the arduino's ADC reference voltage. The
ardiuno Uno's stated ADC absolute accuracy is +/- 2 LSB
So let's say that everything else is perfect and we only consider the
ADC absolute accuracy. That means that our ADC could have read anywhere
from 69 to 73. Those values translate to 0.9445 mW to 1.057 W. That's
only two significant figures at most.
On the higher end of the scale the ADC absolute accuracy will still
impact our values (because we're squaring the voltage). 100 watts in,
99.98 volts peak, (do the above math), gets between 98.32 watts and
99.44 watts. Again, two significant figures. Add to this resistor
errors, reference errors, and non-linearity of the ADC and I think that
the 4 significant digit display is misleading and doesn't reflect reality.
The potential bug is in the CalculateWatts subroutine. This code is
passed the binary value of the ADC. The code then adds a constant
"DIODEVOLTAGEDROP" which is defined as 0.7. I understand that they were
trying to correct the peak voltage reading by compensating for the diode
voltage drop, but in this part of the code the value is not in volts. It
is a binary reading of the ADC, equal to about 0.3448 volts per bit. To
properly correct for a 0.7 volt diode drop they should add 2, which
would be 0.6896 volts. I could be dead wrong, so if others out there who
are more code savvy than me could correct me I'd appreciate it.
I'd love to hear what you folks think about this, as well as the
potential bug in the software.
Thanks for reading
Mike M.
KU4QO
--
bark less - wag more
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Re: Resolution, accuracy, error and digital displays
Some thoughts...
When reading DC (derived from RF rectifier) on the Arduino ADC... - Read the ADC twice to allow for settling of the charge-capacitor in the ADC.
- Set variables as "float" so that the read will return a fractional value.
x = float, y = float;
x = analogRead(ADC_Pin);
x = analogRead(ADC_Pin);? // returns 0 to 1023 in 0.00488V steps
y = x * (5 / 1023);
If the rectifier diode drop is a problem, then use an AD8307 log detector.
Arv K7HKL _._
On Mon, Nov 5, 2018 at 5:34 PM Michael Maiorana < zfreak@...> wrote: Into the deep end indeed. Of course there is likely no practical need to know our output power down to the milliwatt. No doubt that the software can be configured to display as many significant figures as we'd like. The question is, at least in this particular case, how many should we be displaying? Since we talk about test equipment here I thought it would be a worthwhile exercise.?
I got home from work today and read the article, then got the extras from the arrl "in-depth" website. I'm extra confused now since I shyly think that there is a bug. I'll get to that later.
I'm going to start with using 4 significant figures in the measurements. Let's say we're only looking at a pure sine wave, which I think is a reasonable abstraction. We turn up our ultra-accurate QRP rig and put exactly 1 watt (30 dBm) into the 50 ohm dummy load. That should be 7.071 V rms or 9.998 V peak. The diode / capacitor detector circuit should read peak voltage. From there the voltage is reduced to allow more range in the 0-5V arduino input, so a voltage divider divides by 29. So the voltage at the ADC would be 0.3448 V. Each bit in the arduino ADC is 4.883 mV per bit. That math gives 70.60, but it is binary so round to 71? The code averages 30 readings to smooth the reading. It then squares the ADC reading and divides by the load resistance, then multiplies by a "Calibration Offset" of 0.008704. The grand total is 877.5 milliwatts. Since that "Calibration Offset" value is meant to be used for calibration, in this example we'll use 0.009919 since that makes our numbers work. 71 squared, divided by 50, time 0.009919 is 1.0000.?
The issue I started with is possible error, and the displayed 4 digit value in watts. What are the possible errors? The diode drop. The tolerance of the resistors in the voltage divider network. The temperature coefficient of the load resistors. The linearity of the arduino ADC. Accuracy of the arduino's ADC reference voltage. The ardiuno Uno's stated ADC absolute accuracy is?+/- 2 LSB
So let's say that everything else is perfect and we only consider the ADC absolute accuracy. That means that our ADC could have read anywhere from 69 to 73. Those values translate to 0.9445 mW to 1.057 W. That's only two significant figures at most.?
On the higher end of the scale the ADC absolute accuracy will still impact our values (because we're squaring the voltage). 100 watts in, 99.98 volts peak, (do the above math), gets between 98.32 watts and 99.44 watts. Again, two significant figures. Add to this resistor errors, reference errors, and non-linearity of the ADC and I think that the 4 significant digit display is misleading and doesn't reflect reality.?
The potential bug is in the CalculateWatts subroutine. This code is passed the binary value of the ADC. The code then adds a constant "DIODEVOLTAGEDROP" which is defined as 0.7. I understand that they were trying to correct the peak voltage reading by compensating for the diode voltage drop, but in this part of the code the value is not in volts. It is a binary reading of the ADC, equal to about 0.3448 volts per bit. To properly correct for a 0.7 volt diode drop they should add 2, which would be 0.6896 volts. I could be dead wrong, so if others out there who are more code savvy than me could correct me I'd appreciate it.
I'd love to hear what you folks think about this, as well as the potential bug in the software.
Thanks for reading?
Mike M. KU4QO
On Mon, Nov 5, 2018 at 1:25 PM Alan de G1FXB via Groups.Io <g1fxb= [email protected]> wrote:
Hi Mike,
Couldn't? agree more.
Before you take in account the measurement accuracy,
No mater how many digits there are, the least significant digit is
subject to +/- 1 rounding, so is to be ignored.
We had apprentices bringing in their latest purchase 4 1/2 digit
DVM's and the first thing we do is point out in 99.999% of cases
that accuracy is at best unnecessary / and misleading.
60 years ago we made do without needing that accuracy.
When trying to align something for a peak or minimum, Auto ranging
& flickering last digits are a PITA.
Use an analogue meter, alternately it's the reason why better DVM's
have the bargraph function to see trends.
*MOST* voltages quoted in manufactures service
manuals have a tolerance of at least 5% (10% is not unusual) 10v =?
anything in the range 9.5 --> 10.5v (9 -->11v) is allowable.
Does the fact I read 10.501v mean I should look for a fault, while
10.5v is OK??
All but the very cheapest DVM's suffice, and are expendable when the
apprentice over current or inadvertently leave the meter on
resistance range while they put the prods on the mains line in
strip.
It reminds me of a saying. A man with a clock knows the time, a man
with two clocks in probability doesn't.? :-[
Alan
On 05/11/2018 14:23, Michael Maiorana
wrote:
I was looking
over the latest QST magazine and I had a thought that I wanted
to discuss with the group. On the cover was an interesting
"dummy load" project that used an array of resistors in an oil
bath as the load, and an Arduino Nano to display the output
power.?
A voice from my
past echoed in my head. Dr. Wolfe taught Chemistry at the
community college that I attended. He was bright and
energetic, but quite strict. I learned a lot from Dr. Wolf,
but the one thing that has stuck with me over the years was
his insistence on properly expressing values considering the
measurement accuracy and significant figures.
The display on
the watt meter on the cover of QST shows 4 figures of
accuracy. What I wanted to discuss was if it was reasonable to
display 4 digits of precision in this particular instance.?
This is
certainly not a criticism of the QST project, but simply an
opportunity to discuss the topic.
73
Mike M.
KU4QO
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Re: Resolution, accuracy, error and digital displays
Into the deep end indeed. Of course there is likely no practical need to know our output power down to the milliwatt. No doubt that the software can be configured to display as many significant figures as we'd like. The question is, at least in this particular case, how many should we be displaying? Since we talk about test equipment here I thought it would be a worthwhile exercise.?
I got home from work today and read the article, then got the extras from the arrl "in-depth" website. I'm extra confused now since I shyly think that there is a bug. I'll get to that later.
I'm going to start with using 4 significant figures in the measurements. Let's say we're only looking at a pure sine wave, which I think is a reasonable abstraction. We turn up our ultra-accurate QRP rig and put exactly 1 watt (30 dBm) into the 50 ohm dummy load. That should be 7.071 V rms or 9.998 V peak. The diode / capacitor detector circuit should read peak voltage. From there the voltage is reduced to allow more range in the 0-5V arduino input, so a voltage divider divides by 29. So the voltage at the ADC would be 0.3448 V. Each bit in the arduino ADC is 4.883 mV per bit. That math gives 70.60, but it is binary so round to 71? The code averages 30 readings to smooth the reading. It then squares the ADC reading and divides by the load resistance, then multiplies by a "Calibration Offset" of 0.008704. The grand total is 877.5 milliwatts. Since that "Calibration Offset" value is meant to be used for calibration, in this example we'll use 0.009919 since that makes our numbers work. 71 squared, divided by 50, time 0.009919 is 1.0000.?
The issue I started with is possible error, and the displayed 4 digit value in watts. What are the possible errors? The diode drop. The tolerance of the resistors in the voltage divider network. The temperature coefficient of the load resistors. The linearity of the arduino ADC. Accuracy of the arduino's ADC reference voltage. The ardiuno Uno's stated ADC absolute accuracy is?+/- 2 LSB
So let's say that everything else is perfect and we only consider the ADC absolute accuracy. That means that our ADC could have read anywhere from 69 to 73. Those values translate to 0.9445 mW to 1.057 W. That's only two significant figures at most.?
On the higher end of the scale the ADC absolute accuracy will still impact our values (because we're squaring the voltage). 100 watts in, 99.98 volts peak, (do the above math), gets between 98.32 watts and 99.44 watts. Again, two significant figures. Add to this resistor errors, reference errors, and non-linearity of the ADC and I think that the 4 significant digit display is misleading and doesn't reflect reality.?
The potential bug is in the CalculateWatts subroutine. This code is passed the binary value of the ADC. The code then adds a constant "DIODEVOLTAGEDROP" which is defined as 0.7. I understand that they were trying to correct the peak voltage reading by compensating for the diode voltage drop, but in this part of the code the value is not in volts. It is a binary reading of the ADC, equal to about 0.3448 volts per bit. To properly correct for a 0.7 volt diode drop they should add 2, which would be 0.6896 volts. I could be dead wrong, so if others out there who are more code savvy than me could correct me I'd appreciate it.
I'd love to hear what you folks think about this, as well as the potential bug in the software.
Thanks for reading?
Mike M. KU4QO
On Mon, Nov 5, 2018 at 1:25 PM Alan de G1FXB via Groups.Io <g1fxb= [email protected]> wrote:
Hi Mike,
Couldn't? agree more.
Before you take in account the measurement accuracy,
No mater how many digits there are, the least significant digit is
subject to +/- 1 rounding, so is to be ignored.
We had apprentices bringing in their latest purchase 4 1/2 digit
DVM's and the first thing we do is point out in 99.999% of cases
that accuracy is at best unnecessary / and misleading.
60 years ago we made do without needing that accuracy.
When trying to align something for a peak or minimum, Auto ranging
& flickering last digits are a PITA.
Use an analogue meter, alternately it's the reason why better DVM's
have the bargraph function to see trends.
*MOST* voltages quoted in manufactures service
manuals have a tolerance of at least 5% (10% is not unusual) 10v =?
anything in the range 9.5 --> 10.5v (9 -->11v) is allowable.
Does the fact I read 10.501v mean I should look for a fault, while
10.5v is OK??
All but the very cheapest DVM's suffice, and are expendable when the
apprentice over current or inadvertently leave the meter on
resistance range while they put the prods on the mains line in
strip.
It reminds me of a saying. A man with a clock knows the time, a man
with two clocks in probability doesn't.? :-[
Alan
On 05/11/2018 14:23, Michael Maiorana
wrote:
I was looking
over the latest QST magazine and I had a thought that I wanted
to discuss with the group. On the cover was an interesting
"dummy load" project that used an array of resistors in an oil
bath as the load, and an Arduino Nano to display the output
power.?
A voice from my
past echoed in my head. Dr. Wolfe taught Chemistry at the
community college that I attended. He was bright and
energetic, but quite strict. I learned a lot from Dr. Wolf,
but the one thing that has stuck with me over the years was
his insistence on properly expressing values considering the
measurement accuracy and significant figures.
The display on
the watt meter on the cover of QST shows 4 figures of
accuracy. What I wanted to discuss was if it was reasonable to
display 4 digits of precision in this particular instance.?
This is
certainly not a criticism of the QST project, but simply an
opportunity to discuss the topic.
73
Mike M.
KU4QO
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DuWayne Schmidlkofer
K9HZ