Measuring FM Deviation using the MIN/MAX Method (030b)
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- Опубликовано: 3 окт 2024
- In this video I will be showing you how to measure FM Deviation using what I call the "MIN/MAX" Method.
This provides the peak-to-peak deviation. If you are interested in the peak deviation, then divide by 2.
To do this you will need a Spectrum Analyzer.
Yes, I did notice that the MIN hold envelope for this radio is a bit funky. Normally they will be very similar to the MAX Hold trace, just narrower. I don't know what is up with that....yet.
Time Markers for Your Convenience
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00:05 Introductory Comments
01:01 What do we need to do this?
01:38 CAUTIONS
02:01 Spectrum Analyzer Settings
02:52 Test Setup-the Tour
03:33 Making the Measurement
07:12 The Special Case of the CTCSS Tone
09:47 Final Comments and Toodle-Oots
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Excellent video! Thanks for sharing your knowledge.
Thanks so much! ... and you are very welcome! 🙂
An excellent work. I learn a lot when I watch your videos. Thanks . GBY🙏
Thanks man! Glad it was a blessing to you! 🙂
nice work
Thanks
Your video is very interesting. I don't understand why you recommend using a 100 or 10 Hz RBW but in the video you use a 3 KHz RBW. Did I see wrong? Thank you :)
At 1:19 I said that we need a "frequency resolution" of 100 Hz or better. This means the ability to discern between any two adjacent frequencies. This is *not* RBW. At 2:26 I tell folks to set the RBW to 3 KHz.
So, you didn't see wrong. There was just a bit of misunderstanding about what I meant by "frequency resolution." You are good! 🙂
Wouldn't you divide the end number by 2?
When testing a monoband 10 m FM transmitter with your method. I'm coming out with approximately 6.125 kilohertz deviation.
I think realistically the number should to be divided by 2.
I don't think my transmitter is designed to produce 6.125 kHz of FM deviation on 10 meter.
Actually ... yeah, 6 KHz deviation is about right for peak-to-peak deviation. If you are interested in peak deviation, then you are right, divide by 2.
I just added this note to the description for the video.
I hope this makes sense.
@@eie_for_you yes ,PEAK deviation (the one divided by 2) is the measurement most radio testers are interested in. As this PEAK (not peak to peak) is what is shown in the radio specifications for almost all commercial and amateur / HAM radios.
Thanks for the videos!
73!
@@eie_for_you Great video by the way!
Also really appreciate your emphasis on how important attenuation to the test at hand.
It could be a very costly mistake otherwise.
@@mostlypostie1 My oversight in not including it in the video itself.
@@ScottsRadios Thanks!
Great video!
Short question, why are you measuring the first deviation at -40db and then the CTCSS deviation at -30db? Is there a reason why you choose this levels?
Thanks! I was a *fun* video to make! 🙂
To answer your short question.
I was looking for convenient places where both signals pass a particular dB graticule giving me a nice trace to work with, traveling in the semi-vertical direction. The reason is that I am interested in both the horizontal and vertical points of each trace; we want to pick a "well-behaved" spot to make the measurement.
Measuring the deviation of the audio of the radio gave me a particularly nasty min trace to select an appropriate spot to use.
@@eie_for_you Dear Ralph
Thank you for the superfast answer! I am a but confused because it seems that the space between the two points increases with lower levels, does that not mean that the deviation measured at -30db is less than on -40db?
@@Atreju93 Appearances are somewhat deceiving. Because of the curve of the traces and the existence of the graticules on the screen, things can look to the eye what they are not in reality. Still, we *do* want to try to pick a point mid-height as opposed to at the base or peak. We also remember, this is not a "high-precision" measurement.
@@eie_for_you Thank you very much for your explanation! I will try this at home :)
@@Atreju93 I think the deviation is what it is. Why the difference is an unknown to me. But, if it truly is (as measured with the cursors) wider at the bottom and narrower at the top, then making the measurement in the middle gives you kind of an average value. Again, this is not a high precision measurement. Higher precision with a more definitive answer can be found using the Bessel Null method (ruclips.net/video/4XoHmqjen6Q/видео.html).
Terminology is the difficult part of testing and understanding. Peak to peak vs. peak seems to get unmentioned in most FM discussions including those from ARRL.
Very true! And, I made that exact mistake in this video! That is why I added the following note to the description, "This provides the *peak-to-peak* deviation. If you are interested in the *peak* deviation, then divide by 2."