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Post by End80 on Feb 19, 2017 1:38:34 GMT
A couple years ago ISS made this announcement concerning their TIS transmitters: www.theradiosource.com/articles/news-2015-nov.htm
New Travelers Information transmitters installed by Information Station Specialists will sound better than ever. 67% better, in fact. That’s how much wider the bandwidth of the new TR6000 “HQ5.0” Transmitter is compared with predecessors. Moving from the older 3000Hz bandwidth to 5000Hz doesn’t sound like that big of a deal until you recognize that contained within that new 2000Hz slice of audio spectrum is all the “consonance” of human speech – all the brightness, the t’s and the s’s that are so critical to intelligibility.
This got me to wondering what kind of bandwidth the various part15 transmitters put out, and how it varies between Rangemasters, SStran 3000 & 5000s, Procasters, Talking Houses, and IAMs, etc.
I didn't see any specifications addressing this anywhere. Who knows this kind of stuff?
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Post by Deleted on Feb 20, 2017 0:42:46 GMT
Bandwidth on AM Medium Wave
First let's understand what End80 quotes regarding the Traveler's Information transmitter: "Moving from the older 3000Hz bandwidth to 5000Hz doesn’t sound like that big of a deal until you recognize that contained within that new 2000Hz slice of audio spectrum is all the “consonance” of human speech – all the brightness, the t’s and the s’s that are so critical to intelligibility".
The FCC rules for Traveler's Information Stations (TIS), Part 90, up until about 2010 required that the AM transmission systems serving that purpose be intentionally limited to a bandwidth of 3 kKh for no other reason than to make the stations as unappealing to the ear as possible. It was the N.A.B. who lobbied for this crippling limitation in their overly-zealous push to keep their member AM stations from having even the slightest competition. To accomplish the limited audio bandwidth there was required filter circuitry, a low pass filter, for transmitter's to be approved for TIS.
Successful efforts by Information Station Specialists later got the FCC to relax the ridiculous narrow bandwidth and allow a better, but still limited, audio bandwidth of 5 kHz.
The audio bandwidth of part 15 transmitters is theoretically limited not by the transmitters but by the AM channel rules for medium wave, antenna effects on signal bandwidth, and the poor design of some AM radios.
The FCC NRSC rule allows stations to widen bandwidth out to about 10 kHz including a pre-emphasis peak in the high end to make stations sound "brighter".
One might think that because AM channels (dial positions) are 10 kHz wide that the bandwidth is already 10 kHz, but the truth is that the audio bandwidth of a 10 kHz channel on the dial is only 5 kHz! Maybe someone else would like to explain why that's true.
Well designed AM transmitters actually pass more audio bandwidth than is heard at the receiver... receivers have their own bandwidths depending on how their tuning section is designed. Some radios have a bandwidth switch for wide or narrow.
Antenna systems with very high Q are apt to crimp the band-pass of the bandwidth handled by the antenna. It is commonly said that wider antennas, such as copper pipes, have greater bandwidth than very thin wire antennas.
For my AM transmissions I have the bandwidth in StereoTool, the audio processing software, set for 80 to 15 kHz, which gives me a splash that reaches out-of-channel during very high frequency audio, but interestingly there's not that much high-frequency information in my programs, and there are no essential stations directly next-door to my dial slots.
You can tell which stations are operating with wide or narrow bandwidth by how much or how little they splash into adjacent channels.
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Post by End80 on Feb 20, 2017 1:34:00 GMT
I'm not sure if you answered my question.. or maybe you did, but now I'm actually more puzzled than I was.
However a couple thing you said reminded me of something I have a very vague understanding of.. Carl said " For my AM transmissions I have the bandwidth in StereoTool, the audio processing software, set for 80 to 15 kHz, which gives me a splash that reaches out-of-channel during very high frequency audio, but interestingly there's not that much high-frequency information in my programs, and there are no essential stations directly next-door to my dial slots.
It is my understanding (vaguely) that to increase AM range, particularly with part 15, you want to filter out the frequencies that people aren't going to hear anyway which in turn will increase the efficiency of your signal by allowing more of your signal to ride the carrier and go farther... Ahhh.. something like that, I need to look it up again. I don't grasp it well, if I did then I would write about it in my blog, but that's kind of the gist of it. Something like that..
Perhaps I should shut up, things never make sense when I talk out my ass.
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Post by End80 on Feb 20, 2017 1:42:19 GMT
So Carl you indicate that our stations are at it's lowest extreme 5 khz, which is equal to the TIS stations at their highest extreme.
I guess you did my answer my question
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Post by Deleted on Feb 20, 2017 2:06:06 GMT
Abso Talkin Lutely
End80 Radio correctly said: "It is my understanding (vaguely) that to increase AM range, particularly with part 15, you want to filter out the frequencies that people aren't going to hear anyway which in turn will increase the efficiency of your signal by allowing more of your signal to ride the carrier and go farther."
That is exactly why I have no audio below 80 Hz!
Average loudspeakers will not produce frequencies below 80 Hz, speech has no frequencies below 80 Hz, but the heavy bass in many recordings can eat up a lot of modulation energy that serves no purpose, that's why I filter it out.
The other coin of the two sides is that frequencies up to 15 kHz at the top end add the sense of "liveness" and are very useful if the radio manages to reproduce them.
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Post by End80 on Feb 20, 2017 2:35:37 GMT
Currently my broadcast is as bare bones as it can get; just a tablet and a transmitter. All my processing equipment packed away, my automation is simply Media Monkey, no processing plugins available which can be installed on a Surface RT tablet, the only kind of processing I have is MMs built in equalizer. Fortunately my programming is primarly talk and this is the setting I use to make it sound acceptable, and believe it or not, it doesn't sound half bad.
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Post by End80 on Feb 20, 2017 2:44:09 GMT
Now that seems to not correspond really to what I think you said, but it's the way it compares best to ear with other local licensed broadcast. I've experimented different ways.
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Post by Deleted on Feb 20, 2017 3:45:52 GMT
The smaller the bandwidth, the greater the potential range (it takes more power to push a larger bandwidth through the 'ether'). That's one of the reasons why SSB (used in amateur radio & marine) has a much greater range (there's no carrier to eat up power, and the bandwidth is relatively small).
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Post by Deleted on Feb 20, 2017 4:17:09 GMT
That's the NRSC CurveEnd80 has invented a perfect NRSC curve: " This is the setting I use to make it sound acceptable, and believe it or not, it doesn't sound half bad." That's the curve that does the job! You are a very good at making the station sound right. The NRSC Curve According to PhilB
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Post by mark on Feb 20, 2017 5:36:27 GMT
Carl...to answer your question, each station has 10klz spacing(bandwidth) but if you think of it like this....there's a center line which will represent a carrier with no modulation. You can deviate max 5klz on each side of center...total 10klz. With FM you have a 150klz bandwidth....75klz each side of center. FM also has an extra 25klz on each side which is an extra unused "guard band" for a total 200klz for each station. Our transmitters also have to operate in these parameters
Mark
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Post by Druid Hills Radio on Feb 20, 2017 14:19:53 GMT
Rangemaster 1000: 20-20Khz +/- 2db (older units were +/- 3db, Sstran: 20 - 20 kHz ± 0.5 dB
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Post by Admin on Feb 20, 2017 14:44:34 GMT
As unlicensed intentional radiators under Part 15 rules, our transmitters may operate with whatever form of modulation is desired and I don't see any restriction on bandwidth other than outside of the allowed band of operation.
From the FCC OET Bulletin No. 63, they quote FCC Part 15.205 and 15.209 and state "If a particular transmitter can comply with the general radiated limits, and at the same time avoid operating in one of the restricted bands, then it can use any type of modulation (AM, FM, PCM, etc.) for any purpose.
Now of course it does no one any good if the type of modulation is not compatible with receivers designed for the band of operation, i.e. audio frequencies outside the bandwidth of the receiver.
Edit: Closer look indicates FM band does restrict emitted signal to 200 kHz bandwidth within the band however I can't find any modulation bandwidth limit for AM band.
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Post by End80 on Feb 20, 2017 15:28:11 GMT
Mine's the older units. I thought the only difference was the use of crystal as opposed to an agile adapter units
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Post by mighty1650 on Feb 20, 2017 15:40:27 GMT
The Rangemaster has had a few component upgrades over the years that have slightly improved the audio and power performance. Of course the Rangemaster has always been way overbuilt so just how noticeable these changes have been is unknown to me.
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Post by Deleted on Feb 21, 2017 17:37:53 GMT
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