This thread has degenerated. I am going to close it unless the insulting stops. Kelly is a recognized expert radio, TV and related field engineer... a little respect, please.
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Over modulating
- Thread starter 192khz
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The problem starts when he says RTL-SDRs are toys. This is totally wrong. Coming from someone that is a expert is very unexpected. Any SDR will give extreme linearity with a reasonable good construction. including correct electrical circuit and a proper USB isolation to prevent CPU and other things interferences.
They are experimenter's and hobbyist's gear, not professional. That is why they are not approved in nations with stringent technical standards for licensed FM broadcast transmission. I know that they were not allowed in several nations where I have involvement, such as Argentina and Ecuador.
Can a licensed FM in Brasil use one of them? Do you know of any nation where they are allowed for full power licensed stations as an exciter or for relay or shadow fill situations.
I get it. You consider the term 'toy' as demeaning to a device you enjoy using. David put it well; they are great for experimenters or hobbyists. As long as one doesn't assume a station is in violation without backing it up with professional test methodology and gear, have fun with the SDR.
Preemphasis only creates problems with managing levels when it comes to controlling peaks within the window of those frequencies. Enhance a certain part of audio spectrum means there's just more to manage, and the risk of creating harmonics when limiting it. Back in the analog processing and analog stereo generator days, 'filter ring' used to be a problem. When hit with enough energy, the 15kHz Low Pass Filter to protect the pilot used to ring, creating additional products that would show up as inaudible modulation peaks.
And worse was the crunching or popping noise that some cheap receivers would make when a station over-modulated severely. Higher frequency audio could "screech" in such cases.
In several places outside the US where I used cutting edge processing competitors just thought that we were over-modulating and turned their own levels up. The result is that they sounded distorted, while we sounded crisp and clean.
Too few managers today recognize that great engineering can be a significant competitive advantage.
Measuring FM modulation means accurately determining frequency deviation of the RF carrier. Measuring AM modulation means determining how close to zero the total RF signal is. Presumably a software designed radio could do this with great precision, if it were designed to do so.
I have yet to find a DX community online SDR that receives FM broadcast. Obviously, today the SDR and DSP concept is foundation of nearly all multifrequency receivers today.
Is there a low-cost SDR that specifies its demodulated audio frequency response at MW?
I have yet to find a DX community online SDR that receives FM broadcast. Obviously, today the SDR and DSP concept is foundation of nearly all multifrequency receivers today.
Is there a low-cost SDR that specifies its demodulated audio frequency response at MW?
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I've seen some inexpensive ones that will go down to 100kHz and as high as 1gHz. They'll give you waterfall or rudimentary spectrum displays. Signal Hound makes some pretty high end SDR's for the Cell and PCS industries which also cover the FM broadcast band. Most of those are mainly used for application-based USB spectrum analysis.
Kelly A- Then I suppose the online SDR DX community is not interested in hearing FM broadcast signals from around the world. That is too bad, because many locations that are poor for MW reception are excellent for FM reception. Someone said the online SDR DX community is small. I think it might be much bigger if FM broadcast SDR listening was widely available.
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Like anything, I imagine it's because manufacturers build devices to meet demand. DX'ing is a pretty small sector as hobbies go anyway, so if the demand for devices that cover both MW and FM equally well aren't sought after by enough consumers, one can't expect to readily find them. That being said; I'm not a DX'er, but I know one who has several different SDR's depending on the band, including FM broadcast and all the various amateur bands. He's pretty into it.
In Brazil SDR usage is increasing every day on all stations, small community stations to top 10 huge markets. It is considered a very solid solution for modulation measuring as it perfectly matched all the results of expensive as hell equipment like a brand new Teletronix modulation monitor. Some people make portable monitoring hardware with a small windows 10 tablet and good quality SDRs like the modded metal SDRs boxes. they even add external power from good and stable batteries for completely isolating the eletrical circuit from computer CPU noise on ground. I know some stations running on DEVA SDRs as well. the receiver is good quality but the modulation metering is very imprecise.
This sounds like the same "cheaper solution" that I found when I wanted my first FM to go to stereo broadcasting around 1967. Along with my consultant, we modified a Philips test bench FM receiver tester; we used the stereo generation circuit and added an audio input to it. We made the power supply more stable, and we generated the first FM stereo signal in Ecuador on HCTM1 for about 10% of the cost of a "real" stereo generator. And, yes, it had decent separation and people noticed that it was truly stereo.
Regarding FM analog modulation monitoring- it is correct that accurate measurement requires having the equipment and process necessary. For 40 years broadcast FM exciters have had sufficient metering to determine peak modulation, and for longer than that audio processors have controlled peaks. Even with semi-pro equipment it is possible to get modulation within reasonable compliance.
"Why don't I sound like that" is usually not about modulation level.
Several times I have heard stations that were so big and larger than life, the first impression is they MUST be overmodulating. When I investigated, they were not overmodulating at all. They were just simply very good at what they intended to do.
"Why don't I sound like that" is usually not about modulation level.
Several times I have heard stations that were so big and larger than life, the first impression is they MUST be overmodulating. When I investigated, they were not overmodulating at all. They were just simply very good at what they intended to do.
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100% correct. A superior-sounding station starts with the performance of the audio chain from the mic to the antenna, and include factors like a good broadband transmission system. I've been called to look at FM stations who threw tons of money at new audio processing, mic processing, and even an audio console, but can't sound as good or better than their competition. After looking at the carrier with proper test equipment, discover the asynchronous AM noise is -22dB, or their old dual Marti STL is causing phase shifting at certain frequency ranges, like Harris Digit exciters with dried out caps, or one of my favorites; two bays of an antenna that were no longer connected.
I inherited a Class B FM in San Juan, PR, in the 70's. The FM had a licensed 50 kw ERP but could not be heard 10 miles from the transmitter site.
The sister AM could not stay on the air for even a week straight. The FM had been forgotten. I turned them off and started a 5 month rebuild with a new FM site.
When we dismantled the old FM system, we found that the bottom 3 of the 10 bays were disconnected. Apparently the antenna was not kept pressurized, and moisture would enter the antenna (it is never rainy or humid in Puerto Rico, of course). As it condensed at the bottom of the FM antenna, arcing would eat copper away. As the water level increased over time, the bottom bay was disconnected. Then the next on and the next one. The angle of radiation was likely somewhere in the stratosphere.
It went back on the air from the new site and became the top rated FM in the market.
And this brings up my pet peeves about broadcast engineering. First, management sees it only as an expense, not an opportunity. Second, we have fewer and fewer engineers who understand RF and transmitters so the quality of many stations is declining.
On a market like brazil. every cheaper solution you can find is useful. Specially when it comes with a very good precision like the SDRs. I do have several modulation monitors. and they keep showing exactly the same results. (within 10% of difference for less or equally precise peak precision). Everyone moved on to software audio processing as well. With advantage of DC Coupled soundcards like the SMSL DACs or Hifi-Berrie's. But remember, Not every station is like that, we have very big stations with several problems, I know some guy who thought 100khz reading were 100% modulation readings on a transmitter display. all the 5 stations he worked were at 100khz modulation index... This is Brazil David, not for everyone...
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