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Diode Power Meter prototype
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- เผยแพร่เมื่อ 18 ส.ค. 2024
- As I'm known as the guy that never finishes a project, here is another one!
This RF power meter uses a zero bias diode detector to measure the incident power over a 50ohm termination load.
The power meter head provides a voltage proportional to the power, that is conditioned and amplified at the frontend.
Using a polynomial regression over calibration data, the measured power can be accurate, displayed on the screen.
At the head, I also used a temperature regulation scheme.
An additional diode junction is used to measure the detection junction temperature. With the help of a small 1206 resistor heater, the Arduino closes the loop, maintaining the detector at a constant 45 degrees.
At the moment, I'm able to test the power meter up to 3GHz. Probably, the design can work up to 10GHz with the BAT15-099 diode I used, if the head is carefully assembled.
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I like your use of the Manhattan style of circuit building!
By far the best prototyping method!!
@@AllElectronicsChannel Well, certainly at least for the higher frequency projects.
very nice, that is a great accuracy, using the heater was a great idea
Nice concept and very impressive performance! This could be turned into a commercial product, but not with that circuit implementation! 😀 I think it's great that young people are studying the work of the old masters, but nowadays it's almost as easy to do a PCB at frequencies below a few GHz...
Take a look on the evolution of the project, videos are here on the channel!
@@AllElectronicsChannel Thanks. I found two later videos where you solved the ESD problem and placed the processing and frequency selection in an enclosure. That's 95% of the way to a commercial product...
This is brilliant, just found your channel and thoroughly enjoying being taught RF. You cover some really interesting topics like neutralisation!
The idea of using a second diode in the package as a temperature sensor is great, as is using a chip resistor to heat. Sensors like the 8481a seem to use thermocouple detectors, but I couldn't see where the "cold" junction was or how they compensate for ambient.
I'm going to tear down my BG7TBL FA-2 later and see if I can figure out how that measures power too. Thanks for the inspiration!
Thank you!! I'm working now to finish the project. The diode is very sensitive to ESD and this is the main challenge, I think.
I uploaded a video talking about it
very clever job, now all your instagram storyes have sense
hahahahahah thanks!
Very nice work.
I like how you use the arduino to control every aspect of the circuit, giving you one centralized controller.
How did you characterize your polynomials?
It seems like a lot of work to do it all by hand.
It is a very useful instrument indeed.
What is the frequency range for the unit?
I would suggest something like 100kHz to 3 or maybe 4GHz?
Greetings,
Michael
Thank you!
For this test, I got the calibration data in a semi-automated fashion.
I made a script to roll over a list of frequencies and powers, waiting to press ENTER after each change.
So I swept from 100MHz to 3GHz in 250MHz steps. At each frequency step, a full sweep of power was made, from -45dBm to 15dBm, in 5dB steps.
With this data, the code fits a 4th order polynomial for each frequency step.
To read the power, as I showed in the video, I made another script.
This one asks the user what is the frequency of interest, grabs the two polynomials around the frequency, and interpolate linearly between the two.
I think that in the final version of the equipment, we can have a knob to select the frequency of interest.
Let's design an automated calibration using GPIB!?
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The BAT15 I used probably can work up to 10GHz... I think the secret is the low inductance layout of the arrangement.
This is brilliant! I have a question though: how would distortion affect the accuracy of the reading? In other words, you are measuring a mostly pure sine wave from the very clean ESG. How would the reading be affected if you fed in a signal with, say in addition to the fundamental, a couple harmonics only 20-25dB down (or possibly worse)? Since the detector is affected somewhat by frequency, wouldn't there be a noticeable shift in the accuracy? Or would the effect be minimal, since the accuracy would mostly only be decreased on the lower level harmonic content, rather than the fundamental?
Thank you!
You are right, this measuring technique will work properly only for pure tones. Even so, I just tested with a 2nd harmonic 10dB below and the reading increases only 0.3dBm.
Increasing more the harmonic power, the reading becomes less accurate.
So, basically, this detector is sensitive only to the dominant tone.
I think that frequency dependent is also a concern only of the main tone measured!
@@AllElectronicsChannel Ok thank you--So it sounds like even with some extremely high harmonic distortion, the absolute readings should be well within a dB, which is still quite accurate. Excellent! I'm looking forward to seeing the finished project. :-D
Can you recommend a list of books to learn analogue electronics? Years and years and i never managed to learn it.
Hello!
Analog electronics is a art.. the best way is to go to the bench and test the circuits..
One good book with an general overview is The Art of Electronics.
I learn a lot reading service manuals of old HP and Tektronix equipments, there you will learn a lot of black magic.
Follow me on Instagram! @allelectronicsgr
@@AllElectronicsChannel Thank you.
Can you tell me the diode and front end op amp name you used.I have some germanium diode laying around.Can i use it with this circuit??
Hey! The diode is a BAT15-099 and opamp a jellybean LF347, any opamp with low input bias current will work if you trim the voltages offsets!
Make the test with your germanium diodes, I'm curious to see the results! I think you will get good operation over the VHF band!
Can you post the schematic?
Yep! In the next video, I will post the complete design. Nevertheless, It's basically what I showed in this video.
@@AllElectronicsChannel thank you kindly for showing this cool design. I have been meaning to make my own power meter too but never got around it
Let's do it!!
Hi,
Can you share schematic please 🙏😊❤.
Regards
Read more here! gusbertianalog.com
@@AllElectronicsChannel thank you, is it possible with it to match reflected power from microwave guide?
Yes! Is has a very stable 50ohm input impedance.
@@AllElectronicsChannel thank you brother 🙏❤