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AM Radio - Directional Transmitter Antenna Systems - Still Needed?

kfbkfb

kfbkfb

With the increasing level of background noise in the AM band, one way to look at the situation is that the AM signal doesn't travel as far as it used to.

AFAIK, Day/Night Directional Antenna Systems were designed to minimize interference with distant AM radio stations, if the signal in effect doesn't travel as far (and potentially interfere), then maybe an omnidirectional AM signal is OK for both Day and Night.


Kirk Bayne
 
kfbkfb said:
With the increasing level of background noise in the AM band, one way to look at the situation is that the AM signal doesn't travel as far as it used to.

AFAIK, Day/Night Directional Antenna Systems were designed to minimize interference with distant AM radio stations, if the signal in effect doesn't travel as far (and potentially interfere), then maybe an omnidirectional AM signal is OK for both Day and Night.
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The signal travels just as far as ever; the laws of physics don't change.

The difference is that low noise levels back in the late 1920's when the AM band was "redesigned" were so low that very weak signals were totally listenable. Today, those signals are overcome by man-made noise.

Individual stations don't interfere with each other any more or less than they did when the Federal Radio Commission was formed about 96 years ago.
 
Seems like the other stations, on the same and adjacent frequencies, would just add even more noise and interference. That would limit reception even more.
I wish everyone would keep an eye on their patterns, power levels and switching schedules. That would help a lot.
 
kenglish said:
Seems like the other stations, on the same and adjacent frequencies, would just add even more noise and interference. That would limit reception even more.
I wish everyone would keep an eye on their patterns, power levels and switching schedules. That would help a lot.
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If every AM went digital, we wouldn't have to worry about it anymore. Either you can decode the bitstream, or you can't.

As David said, not much has changed when it comes to protections. The real issue is; since there is no revenue outside your main market, so all the concern about skywave overlap only matters to a handful of radio nerds. No upside with pleasing DX'er's, because they aren't buying products or services carried on a station they're DX'ing. In other words, the days of an AM station covering several states, and the subsequent owner bragging rights is over.

I'm hopeful that someday the Commission will allow stations on co-or adjacent channels who volunteer to run MA3 mode, to be allowed to run a full 10kW ND day and night, getting rid of their phasors, and multiple towers. One tower, 10kW MA-3 mode, done!
 
Kelly A said:
I'm hopeful that someday the Commission will allow stations on co-or adjacent channels who volunteer to run MA3 mode, to be allowed to run a full 10kW ND day and night, getting rid of their phasors, and multiple towers. One tower, 10kW MA-3 mode, done!
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We could clean the band by about 30% or so if the FCC let AMs with translators turn off the AM. They woul just have to grant some kind of protection to the translator, though.
 
Ending directional antennas is not an idea without merit. After all, two of the reasons AM has been struggling are directional arrays which are too tight to fully cover their modern market (example: WFNI/Indianapolis) or sit on a large plot of land that became more valuable than the station itself (among others, WFME/New York)

1070 is a very crowded frequency in the east. KTNH in Houston uses 9 towers at night. Stations on 1070 in Memphis, Tenn.; Madison, Wis.; Hannibal, Mis.; Sarnia, Ont. and Indianapolis all employ 6-tower DAs to keep mutual interference down, and several other stations have 3, 4 or 5 tower arrays.

The question is what do you do with all the overlaps. If you gave all those 1070 allocations 5kW or 10kW ND, you will get areas of interference. I can't say where they would be without doing some work, but I expect it would be close enough to the station's home markets that it wouldn't be something stations would be excited to try. I'd be interested to see if someone like R.Fry or one of the DXers would have more to say about their experiences on crowded frequencies.
 
you'd have to get Canada, Mexico, and other countries to sign off as there are treaties in place dealing with protection of frequencies in other nations
 
PTBoardOp94 said:
Ending directional antennas is not an idea without merit. After all, two of the reasons AM has been struggling are directional arrays which are too tight to fully cover their modern market (example: WFNI/Indianapolis) or sit on a large plot of land that became more valuable than the station itself (among others, WFME/New York)

1070 is a very crowded frequency in the east. KTNH in Houston uses 9 towers at night. Stations on 1070 in Memphis, Tenn.; Madison, Wis.; Hannibal, Mis.; Sarnia, Ont. and Indianapolis all employ 6-tower DAs to keep mutual interference down, and several other stations have 3, 4 or 5 tower arrays.

The question is what do you do with all the overlaps. If you gave all those 1070 allocations 5kW or 10kW ND, you will get areas of interference. I can't say where they would be without doing some work, but I expect it would be close enough to the station's home markets that it wouldn't be something stations would be excited to try. I'd be interested to see if someone like R.Fry or one of the DXers would have more to say about their experiences on crowded frequencies
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Much of the time I was living in Lafayette, IN, Sarnia was blasting day power. WIBC (at the time) had its 10000 watt night pattern beamed well away from us, but Sarnia was blasting in with oldies every night.
 
I was too brief in my question, in the past (a time of low background noise), at some certain distance from a given AM transmitter, the AM carrier to (background) noise ratio is too low and the AM station can't be heard.

Now, with higher background noise, the AM carrier to noise ratio gets too low at a shorter distance from the transmitter, so it could be that directional transmitter antenna "protection" for distant AM stations on the same frequency as the local AM station
isn't needed, the higher background noise automatically limits the distance of the local AM signal such that it won't interfere with distant AM stations it might have in the (low noise) past.


Kirk Bayne
 
MRBIboredop said:
you'd have to get Canada, Mexico, and other countries to sign off as there are treaties in place dealing with protection of frequencies in other nations
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The only NARBA nations left are those two plus the Bahamas and, sort of, the Dominican Republic.

In Canada and Mexico, AM has been under a long process of being phased out. Mexico moved 80% of its AMs to FM and AMs are really only left in any number in the US border zone and the three or four biggest markets.

But I don't think they want to spend time "rescuing" AM. They have moved on.
 
kfbkfb said:
Now, with higher background noise, the AM carrier to noise ratio gets too low at a shorter distance from the transmitter, so it could be that directional transmitter antenna "protection" for distant AM stations on the same frequency as the local AM station
isn't needed, the higher background noise automatically limits the distance of the local AM signal such that it won't interfere with distant AM stations it might have in the (low noise) past.
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I have not done the complicated interference calculations for night AM, but the fact is that most AMs are protected at night only to fairly high interference free contours to begin with.

While the "most heritage" stations are protected to signal levels that are inadequate to overcome noise today, most are not. So if the protected night contours are reduced further, it will affect the still-listenable areas of AM stations.

The biggest problem of night interference is that it is highly variable. If you increase radiation in heretofore nulls, good stations will get interference in listenable areas more often. And the average listener who can get interference free FM and zero interference streams will just not come back.

Kelly's suggestion of all AMs going digital is the only solution as that way there would be no background interference. HD radio is "either / or" and only one... the stronger, consistent signal, will be listenable. Economically, this is what I would call a really desperate long shot to save AM. I would not invest in it, or any AM today, as I have seen how many nations have simply given up on AM, with even 100 kw major market AMs going silent in recent years.

Instead of beating a dead horse, some are trying to resuscitate it...
 
Kelly A said:
If every AM went digital, we wouldn't have to worry about it anymore.
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I don't understand. Signals would still propagate the same way, skywave signals mixing with local signals at night regardless of whether the transmission mode were analog or digital, no?

I would think that an HD radio would have trouble decoding an all-digital AM signal if there were other skywave digital signals mixing with it, and all you would hear is silence. Or is that not how it works?
 
Theater of My Mind said:
I don't understand. Signals would still propagate the same way, skywave signals mixing with local signals at night regardless of whether the transmission mode were analog or digital, no?

I would think that an HD radio would have trouble decoding an all-digital AM signal if there were other skywave digital signals mixing with it, and all you would hear is silence. Or is that not how it works?
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Digital will simply select the best signal and eliminate all the others. It sort of "locks on" to one and excludes the rest.

Analog allows all the signals on the frequency and even sidebands of signals on adjacent frequencies to all be detected together. So if you are on a graveyard channel (1230, 1240, 1340, 1400, 1450, 1490) 30 to 40 miles from any one station, you may have five, six or more analog signals all jumbled on the channel. DXers use this quality to turn the radio or the antenna to null the stronger signal so that they can at least identify the weaker one(s).
 
DavidEduardo said:
The only NARBA nations left are those two plus the Bahamas and, sort of, the Dominican Republic.

In Canada and Mexico, AM has been under a long process of being phased out. Mexico moved 80% of its AMs to FM and AMs are really only left in any number in the US border zone and the three or four biggest markets.

But I don't think they want to spend time "rescuing" AM. They have moved on.
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Exactly, and since Canada and Mexico have also adopted the same AM IBOC/digital standard, renegotiating existing treaties should be relatively painless. In reality though, at this point in life I doubt the governments want to spend the time nor effort for the MW bands. Especially since there is zero auction revenue options with making such a move. The only reason the U.S., or any government would push to simplify the AM band structure including all digital, is if money was involved.
 
What happens when you are driving, and the digital station you're listening to drops to a level that is significantly lower than another co-channel digital?
Will your receiver simply lock to the undesired station for a few moments, then return to the desired one (after you round the nearby mountain, or come out of the tunnel), or does it seek out new tables and replace the existing ones?
 
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