• Get involved.
    We want your input!
    Apply for Membership and join the conversations about everything related to broadcasting.

    After we receive your registration, a moderator will review it. After your registration is approved, you will be permitted to post.
    If you use a disposable or false email address, your registration will be rejected.

    After your membership is approved, please take a minute to tell us a little bit about yourself.
    https://www.radiodiscussions.com/forums/introduce-yourself.1088/

    Thanks in advance and have fun!
    RadioDiscussions Administrators

FM Modulation Monitor software

F

fl-lpfm

Guest
Is there any software out there that I can use to monitor my station's modulation? And if so, how will it be conected to a nicom usa NT20 Exiter and an N501 Amp.

Regards!
 
I don't think there is anything out there that would really do the job for you strictly based on software. Here's an idea though: http://pira.cz/fm_broadcast_analyzer/ I have found mine to be pretty damn close to most all of the normal Belar, QEI and TFT units I have compared it against. For around 150 dollars it's most likely your best bet on a really tight budget. One thing you could consider just using the computer is to open up a audio editing program and feed audio from the radio into the line in on the computer. Then, go look at others in the market and get a reference level so to speak. Take a look at your station's level. You can sort of get close that way IF you have a radio that doesn't have wierd DSP, soft mute, or blend things built into it. Personally I'd just order the Pira and wait a couple weeks. You'll be happy you did IMHO.
 
OKCRadioGuy said:
One thing you could consider just using the computer is to open up a audio editing program and feed audio from the radio into the line in on the computer. Then, go look at others in the market and get a reference level so to speak. Take a look at your station's level. You can sort of get close that way IF you have a radio that doesn't have wierd DSP, soft mute, or blend things built into it. Personally I'd just order the Pira and wait a couple weeks. You'll be happy you did IMHO.
Click to expand...

I'm afraid that the demodulated and de-emphasized L/R audio level will give you little clue about your actual peak modulation level...


Regarding,
Goran Tomas
 
Let's not forget about MpxTool - http://mpxtool.com

Together with a tuner with MPX output, and some means to calibrate it, it can be a very accurate modulation monitor.


I've tried the PIRA75 - it appears to work pretty well!
The frequency response is not particularly flat (if 1 KHz measures at 100%, 57k measures below 70%) but it IS dc straight (no tilt), and requires no calibration at all, so it is absolutely usable out of the box.

///Leif
 
konbaasiang said:
Let's not forget about MpxTool - http://mpxtool.com

Together with a tuner with MPX output, and some means to calibrate it, it can be a very accurate modulation monitor.


I've tried the PIRA75 - it appears to work pretty well!
The frequency response is not particularly flat (if 1 KHz measures at 100%, 57k measures below 70%) but it IS dc straight (no tilt), and requires no calibration at all, so it is absolutely usable out of the box.

///Leif
Click to expand...


Hello all! Thanks for the sugestions. I got one question about mpx tools. I have read in another site that you can modify Tivoli Model One for mpx output but couldn't find any documentation. Can you help?

Thanks
 
I tied a scope into a FM tuner. Connected it to the demod ahead of the de-emphasis circuit. Tuned in a local station that I knew was set up correctly and calibrated the scope so this station was showing + and - 4 divisions on the screen. I then adjusted the modulation on the station I was working on to the same level on the scope . This may not be a legal way of checking the modulation but when I returned with a regular mod monitor I found it was running about 98% mod. Not to bad for a quick rigged mod monitor. Accuracy will depend on the station you calibrate it against and how close you read the scope.
 
You can indeed modify the Tivoli -- in fact, you can modify almost any tuner.

It's been a long time since I did it, and of course I neglected to document it, but the principle is very simple:

Open the tuner, find the FM/Stereo decoder chip, google the model number, see if it has a Composite / MPX output pin, and then connect something to it. It would be a good idea to have some kind of buffer amp stage between the tuner and the output jack as well, to protect the chip. Make sure it's wide bandwidth and as DC straight as you can make it (large coupling capacitors).


Rew, that is actually pretty good way to do it! The only problem is tilt -- unless the tuner is DC straight, squarewaves will tilt and make it very difficult to find the correct level. Sounds like it worked well for you, though!

///Leif
 
rew said:
I tied a scope into a FM tuner. Connected it to the demod ahead of the de-emphasis circuit. Tuned in a local station that I knew was set up correctly and calibrated the scope so this station was showing + and - 4 divisions on the screen. I then adjusted the modulation on the station I was working on to the same level on the scope . This may not be a legal way of checking the modulation but when I returned with a regular mod monitor I found it was running about 98% mod. Not to bad for a quick rigged mod monitor. Accuracy will depend on the station you calibrate it against and how close you read the scope.
Click to expand...


Years ago I heard an FCC field inspector give a presentation in which he essentially said this is how he does it.

The only difference was that instead of using another station as a reference, he used an RF generator.

He set the generator on fC and set the scope trace for the center.
He set the generator at fC + 75 KHz and made a mark on the screen.
He set the generator at fC - 75 KHz and made another mark on the screen.

As long as you can find the discriminator output, this will work very well.
 
greg.hahn said:
rew said:
I tied a scope into a FM tuner. Connected it to the demod ahead of the de-emphasis circuit. Tuned in a local station that I knew was set up correctly and calibrated the scope so this station was showing + and - 4 divisions on the screen. I then adjusted the modulation on the station I was working on to the same level on the scope . This may not be a legal way of checking the modulation but when I returned with a regular mod monitor I found it was running about 98% mod. Not to bad for a quick rigged mod monitor. Accuracy will depend on the station you calibrate it against and how close you read the scope.
Click to expand...


Years ago I heard an FCC field inspector give a presentation in which he essentially said this is how he does it.

The only difference was that instead of using another station as a reference, he used an RF generator.

He set the generator on fC and set the scope trace for the center.
He set the generator at fC + 75 KHz and made a mark on the screen.
He set the generator at fC - 75 KHz and made another mark on the screen.

As long as you can find the discriminator output, this will work very well.
Click to expand...

Again the accuracy will depend on the reference. In this case - the signal generator. If it's a calibrated signal generator and you are absolutely sure you can trust that 75k is 75k, than it is indeed something you can use to check you modulation against. Though the peak accuracy of your reading will depend on your vision and screen persistence ;) And it probably won't work as good with a digital scope, because most have too slow display response times.


Regards,
Goran Tomas
 
Status
This thread has been closed due to inactivity. You can create a new thread to discuss this topic.


Back
Top Bottom