traveler's info stations AM or FM

[Black_Shire]

Black shire,

When you wrote:

Also, the narrower bandwidth has the effect (whether the rule makers intended it or not, I don't know) of making the signal intelligible at a greater range with the given power than a standard 10 kHz AM signal could be copied.

you perhaps had in mind the equation which predicts noise at a receiver which is

En = SQRT(4*k*T*BW*R)

Intelligibility is related to the signal to noise ratio and this equation predicts that the noise will be reduced by the SQRT of the bandwidth, but unless the bandwidth of the receiver is narrowed, there will be no gain in S/N for a bandwidth limited TIS transmitter as compared to a full bandwidth broadcast AM station. This advantage is a function of the receiver bandwidth and not the transmitter bandwidth.

Perhaps you know of another reason there is an advantage to narrow bandwidth that I missed.

Neil

A 6 kHz wide AM mode signal can be heard farther away than a 10 kHz wide AM mode signal at the same radiated power for the same reason that a CW signal can be heard farther away than an SSB signal (which in turn can be heard farther away than an AM mode signal)--you're putting the same amount of energy into a narrower slice of spectrum, which punches through the noise more strongly.

 

[Neil E.]

In an earlier post Zach asked:

What's the purpose of the rule limiting bandwidth on the TIS?

Zach, my take on this is it is to limit the occupied bandwidth of the TIS signal in order to minimize the possibility of interference with adjacent channel stations.

Neil

 

[rfry]

If you're content to dabble with equations, yes. Those who are more interested in actual Part 15 AM broadcasting would do better to read the works of someone who had decades of actual experience with the hardware and techniques involved in Part 15 AM Community broadcasting, and Mr. Cunningham is that person.

Physics is physics. If your revered Mr. Cunningham truly understood that physics, and if his "Part 15" AM experiences and writings were so based, then no problem.

But if and where his conclusions differ from those proven by many decades of professional engineering investigation, field studies, and field experience in MW applications, then a smart reader will do well to treat such statements by Mr Cunningham and those quoting/supporting him with due skepticism.
//

 

[rfry]

A 6 kHz wide AM mode signal can be heard farther away than a 10 kHz wide AM mode signal at the same radiated power for the same reason that a CW signal can be heard farther away than an SSB signal (which in turn can be heard farther away than an AM mode signal)--you're putting the same amount of energy into a narrower slice of spectrum, which punches through the noise more strongly.

Your concept/belief is incorrect, sorry.

A CW signal can be "copied" better than either an SSB or a DSB AM signal because the r-f bandwidth needed by the receiver for the useful reception of CW is less than needed for SSB and/or DSB AM.

Reducing the transmission channel r-f bandwidth means that the received S/N in that transmission channel will improve, other conditions equal.
//

 

[Neil E.]

Black shire,

Regarding your comments about 6 kHz. AM bandwidth compared to 10 kHz. bandwidth, the sideband power in both cases at 100% modulation is one half the carrier power so limiting the audio bandwidth at the transmitter does not increase the sideband power.

What you say about SSB and CW is true because on a comparative basis with AM for a given transmitter power capability, the sideband power is increased, but it is not in the case of AM transmitters that we were discussing.

Neil

 

[BobOnTheJob]

You can't do this on FM, as THAT IS regulated to power output, but more so.. field strength, 250 mv/3m.

Nope...that's 250uv/3m...huge difference between 250mv & 250uv.

 

[Black_Shire]

If you're content to dabble with equations, yes. Those who are more interested in actual Part 15 AM broadcasting would do better to read the works of someone who had decades of actual experience with the hardware and techniques involved in Part 15 AM Community broadcasting, and Mr. Cunningham is that person.

Physics is physics. If your revered Mr. Cunningham truly understood that physics, and if his "Part 15" AM experiences and writings were so based, then no problem.

But if and where his conclusions differ from those proven by many decades of professional engineering investigation, field studies, and field experience in MW applications, then a smart reader will do well to treat such statements by Mr Cunningham and those quoting/supporting him with due skepticism.
//

[EDIT] you just can't stand the fact that you have been proved wrong about every criticism you've made regarding Part 15 AM broadcasting. It's easy to attack publications you've never read (and are afraid to read).

[EDIT] about Part 15 AM broadcasting (based on zero experience with the hardware) hold as much water as those of a retired airliner design engineer (with zero experience building FAA-licensed homebuilt Experimental Aircraft) presuming to tell Peter Bowers that his decades-old "Fly Baby" homebuilt aircraft designs are flawed. A 747 and a "Fly Baby" are both airplanes, but their similarity ends there. While the physics involved in the flight of both are governed by the same laws of aerodynamics, the methods, techniques, materials, and practices used in both types of aircraft are radically different. The same differences exist between Part 15 AM and full-power licensed AM equipment.

Please do all of us Part 15 AM broadcasters a big favor--go play with your little computer programs by yourself [EDIT]. The rest of us will be happily broadcasting with our Part 15 AM equipment long after you've gone [EDIT]


[EDIT-inflammatory]

 

[techie2]

\\ (7) Travelers Information Stations shall transmit only noncommercial
voice information pertaining to traffic and road conditions, traffic
hazard and travel advisories, directions, availability of lodging, rest
stops and service stations, and descriptions of local points of
interest.

Interesting, considering there is a TIS in my area that has been broadcasting sports play-by-play. I guess that falls into a gray area as a "local point of interest." They aren't running sponsorships though, because the entire broadcast just runs straight through from the remote site and they go dead for breaks.

 

[PaulBWalkerJr]

Yeah, if they run a basketball game solely with talk/speech and no music.. it could technically ruled "in the public interest"

 

[rfry]

[EDIT-quoted portion removed for inflammatory comment] about Part 15 AM broadcasting etc, etc

I won't respond specifically to your personal attack. Readers of our posts will decide for themselves which of us has more credibility, and I don't fear those decisions.
//

 

[RadioFlyerAtl]

It's very upsetting to read comments like those posted by Black_Shire. Personally, I've always noticed those who are insecure or are lacking knowledge tend to be the most defensive. It sounds like the same applies here. I guess some people just mature much later than others.

Richard, I've always enjoyed your insight on topics here and in written publications, and I hope this bad apple of the bunch doesn't deter you from future activity on the boards. From your RCA years to the Harris tenure, we certainly have much to learn from your experiences.

Thanks for sharing your time and knowledge with us.

 

[Tom Wells]

I see a debate much like science/creationism here.

Mr Cunningham's successes certainly cannot be in conflict with truth or reality.
He may have acheived his desired effectiveness, but experimentally must have found areas of cancellation.
Multiple radiators/transmitters must exhibit the directional/phasing issues mentioned.
There is no way to time-coordinate since all listeners are at different distances from multiple antennas.

Seat-of-the-pants is romantic and fun to play with...engineering is studious work and proving that something can work.


I think you two are agreeing, but one says "The proof is in the pudding."
The other says, "I have a recipe for pudding."

Given that more than one recipe will make pudding...

And only some chefs can make some recipes work.....
Some chefs make it up as they go...

I discovered in patent prosecution that among the many other things, the Patent Office doesn't have to be sure your invention will work,
they just have to see no reason why it wouldn't work.

Success can be acheived without rigorous application of theory, but radio as a business must rely on good engineering.

Otherwise, we'd have much wasted power with ineffective coverage.
Years of testing and proofs support the effectiveness of the current AM antennas.

Little time is spent analyzing the less effective antennas, but this does not make them a poor choice for the limited space
or resources of low-power transmitters.

What works, works. It may not be ideal. but it works.

 

[rfry]

... Thanks for sharing your time and knowledge with us.

And thanks for your post. I always hope that my comments might be useful at least to a few people.

 

[menotti1]

10 watts AM on 1610 49 meters.what kind of coverage could one expect on this TIS.

 

[PaulBWalkerJr]

With 10 Watts on 1610, if it was TIS with no audio processing and the low bandiwth.. with properly grounded antenna.......... I'd say 5 miles reliably/solid. ..probably more, but it'd start to drop out quick.

 

[pianoplayer88key]

With 10 Watts on 1610, if it was TIS with no audio processing and the low bandiwth.. with properly grounded antenna.......... I'd say 5 miles reliably/solid. ..probably more, but it'd start to drop out quick.

Some TIS's I have heard / can hear (using a Panasonic RQ-SW10 - almost as good as the Sony SRF-42) from my location (Mt Helix area of San Diego county) include:
890 Cabrillo Nat'l Monument - needs select-a-tenna, but has a fair signal.
1500 Qualcomm Stadium - can barely hear carrier w/o SAT; with SAT has some quieting in my receiver, but no audio.
1610 Chula Vista - barely detectable without SAT, fair signal with SAT. (former - no longer on air AFAIK)
1610 Balboa Park - similar to the Chula Vista one
1620 San Ysidro - very weak, but audible, without SAT
1660 San Diego Convention Center - very weak, but somewhat listenable, with SAT
1690 San Diego Airport - a little weaker than 1660, but still could get some audio, with SAT. (now that 1700 is on the air I can't hear it at all.)
and, now, for the long-haul TIS:
530 LAX Airport - with SAT, and IF I null 540 well enough (although I still get a fair amount of adjacent-channel splatter) I can hear the LAX TIS well enough to listen to it. (Last Sunday late afternoon / early evening (around 7:30pm or so), we were hearing this one on our '02 (approx) Honda Accord car radio in Moreno Valley.)
Oh, I almost forgot about the one or two from DFW airport that I used to be able to faintly hear with the SAT, before the other stations signed on the X-band.

 

[TowerLamp]

Your concept/belief is incorrect, sorry.

A CW signal can be "copied" better than either an SSB or a DSB AM signal because the r-f bandwidth needed by the receiver for the useful reception of CW is less than needed for SSB and/or DSB AM.

Reducing the transmission channel r-f bandwidth means that the received S/N in that transmission channel will improve, other conditions equal.
//

R. Fry I'm more than willing to learn from someone who has some experience in the field. I'd like to expand on the bandwidth question by posing this: I grasp the concept that reduced receiver bandwidth will improve the S/N. But in a DSB AM transmission, is there any merit to the belief that limiting the transmission bandwidth will increase a station's coverage? Provided of course the receiver bandwidth matches that of transmission.

Some seem to hold that for AM broadcast stations transmitting anything above 5kHz is a "waste of energy" since so few modern receivers reproduce much of anything above 3 to 4 kHz. In addition to reducing co-channel interference it is said that the station will also increase its coverage. Any truth to this?

 

[littlejohn]

Depends on whether you keep the output power the same. Kahn's PowerSide did essentially what you suggest, reduced (or eliminated) one sideband. Put the power which was in the now absent sideband into the other one, you've increased coverage.
If memory serves, an AM modulated to 100% will have one half its power in the carrier, and one fourth in each sideband. double up on one sideband and you would increase coverage by the square root of 2, would you not? Assuming the receiver responds equally to a signal with both sidebands and one with only one.
It's been decades since I did much AM, maybe the gurus will correct me here if I messed it up.

 

[rfry]

Some seem to hold that for AM broadcast stations transmitting anything above 5kHz is a "waste of energy" since so few modern receivers reproduce much of anything above 3 to 4 kHz. In addition to reducing co-channel interference it is said that the station will also increase its coverage. Any truth to this?

Reducing transmitted audio bandwidth reduces adjacent channel interference, but not co-channel interference.

If a station maintains the same average modulation level at reduced audio bandwidth as it had with wider bandwidth, then audio performance/"coverage" would be the same to receivers with bandwidths that were still less than was being transmitted.

Reducing audio bandwidth at the tx might enable the station to increase their average modulation in the remaining audio spectrum, because of the loss of the pre-emphasized higher frequencies required for NRSC. In that case, the effective coverage range of the station might improve somewhat, because the S/N of a narrowband receiver is better, then.
//

 

[TowerLamp]

R. Fry,

Thanks, made sense at an intuitive level. Just wanted a gut check from someone in the know!
And roger on the adjacent not co channel interference.