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Modulation Monitor Purpose

S

shreveville

I know there are many bells and whistles on new FM modulation monitors. Please explain their purpose. Does the modulation monitor control actual loudness on the dial or is this the job of the processor? I know it has to be more than just an expensive radio to listen to the quality of your station. I have a Boise Radio for that.

Set me straight.

Thanks
 
It's a very wideband and "flat" receiver, hooked up to an accurate and hopefully calibrated metering system. That's a very simplified explanation, but think of it like your speedometer in your car. The needle doesn't control your speed, it tells you how fast you're going.

The purpose is to make sure your signal is within 100% (75kHz deviation with no subcarriers) and doesn't go over. Kind of like the Price is Right, as close as you can get without going over. The processor takes care of all modulation control.

While your Bose radio may sound "good", it isn't necessarily flat or accurate when it comes to monitoring the audio critically and/or measuring modulation.
 
I don't know if you are a cluster or not, but we use an Invonics which holds presets for all of our stations. We tune out the multipath and it also has an add on RDS unit to check injections and data display. It works quite well for us and is reasonably priced.
 
They are great as long as you periodically verify their accuracy by using more credible test equipment. Using them with an antenna off-air usually proves to be inaccurate. Connected to a sample of the transmitter output is the preferred method of measurement. Some of the better ones can be used for other types of measurement such as synchronous and asynchronous AM noise, sub-carrier injection, etc. Nothing, however, can replace a good oscilloscope and spectrum analyzer.
 
Ah, I had it all wrong. I thought the purpose of a AM mod monitor was to let us hear it's full bandwidth output and remind us of how good AM can sound :).

Seriously, though, it is depressing to listen to the high-quality AM audio output and then contrast it to the output of your car radio.
 
ChiefOperator said:
Ah, I had it all wrong. I thought the purpose of a AM mod monitor was to let us hear it's full bandwidth output and remind us of how good AM can sound :).

Seriously, though, it is depressing to listen to the high-quality AM audio output and then contrast it to the output of your car radio.
Click to expand...

The flat output of an AM mod monitor does sound good, but is typically noise-free only if connected directly to the transmitter, where its incoming RF signal measures in Volts rather than millivolts. The mod monitor sounds best when, if the station is running a realistic amount of pre-emphasis, there is complementary de-emphasis. We all know why that pre-emphasis is there. :p Long, sordid story, right guys?

Anyway, clearly, it's a shame there doesn't seem to be any financial model that would encourage receiver manufacturer(s) to develop DSP-based AM receivers that might categorically reject noise and interference, to allow a wider bandwidth to be heard. I'm intuitively convinced it could be done effectively and, ultimately - with today's cheap and easily-programmed DSP - accomplished with minimal negative impact on receiver prices. Then the receiver bandwidth could be opened up a hair, and eventually the stations might find they could safely jack back pre-emphasis a notch or two.

While I don't see AM going away in the next decade or so even though it generally sounds like caca on the typical receiver, if it could be made more pleasant to listen to I believe it could hold on even longer.

And then I woke up.

Kind Regards,
David
 
David Reaves said:
ChiefOperator said:
Ah, I had it all wrong. I thought the purpose of a AM mod monitor was to let us hear it's full bandwidth output and remind us of how good AM can sound :).

Seriously, though, it is depressing to listen to the high-quality AM audio output and then contrast it to the output of your car radio.
Click to expand...

The flat output of an AM mod monitor does sound good, but is typically noise-free only if connected directly to the transmitter, where its incoming RF signal measures in Volts rather than millivolts. The mod monitor sounds best when, if the station is running a realistic amount of pre-emphasis, there is complementary de-emphasis. We all know why that pre-emphasis is there. :p Long, sordid story, right guys?

Anyway, clearly, it's a shame there doesn't seem to be any financial model that would encourage receiver manufacturer(s) to develop DSP-based AM receivers that might categorically reject noise and interference, to allow a wider bandwidth to be heard. I'm intuitively convinced it could be done effectively and, ultimately - with today's cheap and easily-programmed DSP - accomplished with minimal negative impact on receiver prices. Then the receiver bandwidth could be opened up a hair, and eventually the stations might find they could safely jack back pre-emphasis a notch or two.

While I don't see AM going away in the next decade or so even though it generally sounds like caca on the typical receiver, if it could be made more pleasant to listen to I believe it could hold on even longer.

And then I woke up.

Kind Regards,
David
Click to expand...

Motorola did develop the Symphony DSP chip about ten years ago and was able to do all that you suggested. I rented a car several years ago and believe that the chip was used in the car radio. It had one of the best sounding AM I've heard among car radios and even decoded AM stereo
 
radiorob2.0 said:
David Reaves said:
<snip>
...clearly, it's a shame there doesn't seem to be any financial model that would encourage receiver manufacturer(s) to develop DSP-based AM receivers that might categorically reject noise and interference, to allow a wider bandwidth to be heard. I'm intuitively convinced it could be done effectively and, ultimately - with today's cheap and easily-programmed DSP - accomplished with minimal negative impact on receiver prices. Then the receiver bandwidth could be opened up a hair, and eventually the stations might find they could safely jack back pre-emphasis a notch or two.

While I don't see AM going away in the next decade or so even though it generally sounds like caca on the typical receiver, if it could be made more pleasant to listen to I believe it could hold on even longer.
Click to expand...

Motorola did develop the Symphony DSP chip about ten years ago and was able to do all that you suggested. I rented a car several years ago and believe that the chip was used in the car radio. It had one of the best sounding AM I've heard among car radios and even decoded AM stereo
Click to expand...

You jogged my memory. I remember hearing about how great Symphony was going to be. The preliminary promotional info I can find on the web (published in 2002), makes it sound like a godsend.
http://urgentcomm.com/dealers/automotive/radio_motorolas_symphony_digital/

Then I found this editorial quote from September 5, 2007 Radio World:

"For reasons I cannot explain Symphony was not adopted. It was supposed to be virtually as cheap as the systems already in place but with so much more to offer. What happened? Looks like it never made it to market although Motorola was bombarded with requests for chipset samples."
(Emphasis mine. From http://www.radioworld.com/article/whats-behind-am-receiver-performance/17607)

So, if the specialized Symphony RF DSP chipset did make it to market, what models of radios included it? I'd be very interested in reading some reviews and, if I could locate one, giving it a listen.

Kind Regards,
David
 
The '95 Jeep Cherokee Sport had a very good AM stereo receiver but I have no idea who's technology it used....
 
About 1995, I rented Dodge that had an amazing AM radio. It was hard to tell from FM. Maybe Chrysler Corp. is where you should look.
 
We just gotta get somebody to build an updated version of the Mckay-Dymek tuner. ;D
 
I owned a 1989 Plymouth Voyager, a 1993 Jeep Grand Cherokee, a 2001 JGC and for a couple of months a 1994 Chrysler minivan. All had AM Stereo radios and all sounded incredible, especially in the minivans which had rear speakers in the back hatch. The radios were branded "Infinity" which was known in hi-fi circles as a speaker maker. I think the name is owned by Harman today.
 
BTW a Mod Monitor is so the Program Director can see the meters hit the right side of the meter bezel. Set it to minus 30 reference...

Sparkomatic made a great AM stereo radio, or at least had their name on it. Some engineer had one and would place a cassette in it ALWAYS to cover the name. Selectable bandwidth, GREAT selectivity.
 
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