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Adjusting the Modulation Meter

just get a few folks that you think run setups with clean solid audio to give their opinion on your audio . adjust it high as you can with them agreeing your audio is still clean and easily understood .

or send it to DTB ;)
 
Greatvalue1 said:
I'm wanting to calibrate the modulation meter on a DX979 but I don't have an O-scope. My theory is that if I arbitrarily set the MAX OUTPUT (100% Mod) @ 30W, and run my signal generator through the mic @ 200-250 Hrz (for the tone of my voice), that then I'll be able to adjust the meter for 100% Mod @ 30W.

Is this even a remotely viable way of doing this for my own rig, until of course I can afford to buy and learn the right way to do it?
Click to expand...

no .
 
I think 'Booty' pretty well answered the question. I guess it just depends on how much "remotely viable" you will put up with. Getting it -right- would be pure luck, and not much of it then. I think you'd have better luck doing that modulation percentage thingy with a watt meter than the typical modulation meter. 'Course, that would mean you'd have to know/understand exactly what you were doing. It would have about as much chance of being right as doing it in any way NOT using an o'scope.
- 'Doc
 
I posted a long a.swer tbat got dumped for some reason. May have been my connection. I am at work on my phone. Give anotber hoir or two and I will repost from home. Short answer in the mean time as already stated a couple times is NO.
 
Greatvalue1 said:
I'm wanting to calibrate the modulation meter on a DX979 but I don't have an O-scope. My theory is that if I arbitrarily set the MAX OUTPUT (100% Mod) @ 30W, and run my signal generator through the mic @ 200-250 Hrz (for the tone of my voice), that then I'll be able to adjust the meter for 100% Mod @ 30W.

Is this even a remotely viable way of doing this for my own rig, until of course I can afford to buy and learn the right way to do it?
Click to expand...

Your 'signal generator' (guessing that this is a .wav file and your computer speaker/playback) into your mic is going to change the % of modulation as you either change the mic gain level (radio) or the speaker volume (laptop/PC). Too many variables with no standard measurement.

So no; there is NO WAY that it would even be close to correct.

FYI when a scope is used, you can see how mic volume directly affects the carrier vs modulation waveform. As modulation reaches 100%, the carrier gap diminishes to near/at zero.

That is the preferred target setting for AM.

Carrier w/no modulation:

figure-6.jpg


About 30% modulated carrier:

figure-7.jpg


100% modulated carrier:

figure-8.jpg


Over-modulated carrier:

figure-9b.jpg



A meter may be calibrated to a scope for 100% modulation; but the levels below that number would be skewed and not track correctly. Meters don't follow the same % change as would be seen on a scope.
 
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Greatvalue1 said:
I was expecting just an approximation. Just trying to figure out how to do things on my own, that's all.

1: Don't have an O-scope
2: Can't afford an O-scope
3: Don't know how to use an O-scope
Click to expand...



If your just expecting an approximation then LEAVE IT LIKE IT IS NOW cause that's what it is showing you.

Even if you had a scope guess what it would show you? AN APPROXIMATION. It's a gimmick feature on the radio.
 
Here's why "No" is the only appropriate answer

I know this is an old thread, but no one has really told him WHY "No" is the correct answer. Maybe others can learn from my response if he is not around anymore.

Basically "No" is the only real answer to your question because its a matter of "How can you know where you are going, if you don't know where you are?"

The fact of the matter is that you have no idea if you are above, at, or below 100% modulation with your initial "arbitrary" setting, and the only way to truly judge "where you are" is to view your modulation envelope with a 'scope. This page may give you some insight as to why that is so:
A.M. Tutorial Page 4

And I would also disagree with your contention that 200-250 Hz is equal to your voice. Commercial radios used in aviation have a mic audio bandwidth of 300-2500 Hz. While your voice may be deep, the actual vocalizations that convey speech information fall into the 300-2000 hz range, regardless of how deep your voice sounds. The 'depth' of a persons voice is merely a matter of subharmonics of the speech patterns. So that is the range your calibration tones should be. Virtually all of our aviation radios are calibrated at 1000 Hz with 3 dB down points at 300 and 2500 Hz.
 
Pretty much all two way radios are set at 1000 Hz as that is in the middle of the audio passband. No one has a voice at 250 Hz no matter how they really sound. The originator of this thread is either a troll or a person that likes to ask question but does not like to hear answers if they disagree with him. He asked if it was a viable way to do things and was told by several people "NO" and yet he said "No is not an answer". Go figure. I guess it takes all kinds of people to make the world go 'round.
 

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