AM Frequency of the week: 580

[Schroedingers Cat]

Even before NARBA, in the 1930s, some Regional Channel stations started installing directional antennas. Almost all were two towers, and even those were simple designs, with one tower a parasitic (like a reflector or a director with a Yagi, but with monopoles), or simple phasing using lengths of transmission lines. There is not much control when the pattern changes due to weather and aging components, so they started to install driven arrays with phasing and power distribution circuits. The first three and four tower arrays, appeared by around 1940, and by the early 1940s or so Carl Smith designed a six tower array at WTVN as I recall. Most directiional arrays came about to solve interference issues of stations going from 1000 watts to 5000 watts, especially at night. There are a few that don't seem to make sense, other than to concentrate the signal or avoid prohibited network overlaps. I wonder if David can direct us to particular periodicals that listed details about early DAs. The history cards sometimes tell the number of towers in the array, or those added when changing the pattern, but no technical details beyond that. No one has answered me about early databases that they might have at the FCC. And between Commission and radio studio moves, I doubt if you could find many engineering files that go way back. Most of the people who used to remember these details have left us unfortunately. I miss them nearly every day. During World War II, work was completed on a few DAs, but there were no new arrays authorized until after the War. There were around 40 in 1946 as I read somewhere.

 

[Schroedingers Cat]

Didn't have time to add to the previous thread.

After World War II, stations started to squeeze in betweeen the existing older stations on Regional Channels, and continued to upgrade their facilities. The older rules required stations to be far enough apart to protect each other Day and Night nondirectionally, but many stations wanted more power, so many had to directionalize to do so. Since they were limited to 5000 watts, and there was no power level in between 1000 watts and 5000 watts, stations used many techniques to improve their signal within those constraints. Tall towers compared to wavelength, top loading, sectionalized towers, and directional antennas to favor a particular direction were the main techniques. Class III-As were supposed to be protected from 125 uV/m 10% skywave signals, and Class III-Bs from 200 uV/m 10% skywave signals, theoretically protecting them to 2.5 mV/m and 4.0 mV/m NIFs. This was apprently related to the fact that usually only one interfering station would be near the 10% skywave level at a time. As more stations squeezed in, a more complicated calculation involving all interfering signals, RSS, or Root Sum Square with 50% exclusion with reiterative calculation, was required. The DAs DID WORK WELL if they were maintained, and USED with the proper power level at night. With all the new stations squeezed in, higher power levels, and recently PSSAs are operated, this became much more difficult to enforce. With the decline of AM, budgets are not there to maintain the DAs well. And some people in sales and management don't know anything about skywave and interference issues, and only care about their own station, and not the interference it may create. This goes along with the general decline in technical radio and other technical knowledge and ethics that pervades our society. Business and financial people have taken over the industry, who don't have the particular love for radio present in the early days. The interference model and DIRECTIONAL ANTENNAS REALLY DO WORK quite well though, and if stations are maintained and patterns and powers are properly changed, stations DO have a more listenable signal at night, except really high NIF stations and PSSAs.

Translators solve some of these problems, but lack of technical knowledge and ethics are now creating a problem to established FM signals who are losing de facto coverage all over the place. When a 250 watt translator can blot out previously very listenable FM signals just beyond or at the edges of their service areas, often just beyond small hills, the older models used for FM service and interference prediction are clearly inadequate. The real solution would be an expanded FM band and full power FM stations to replace many AM stations, but no one seems to want to push this issue seriously.

 

[billmich]

thank you for the previous 3 posts, it answered a lot of questions I had regarding class III (regional) channels

 

[Schroedingers Cat]

There are (because no matter how you cut it, they are different) 41 Regional Channels. They are 550, 560, 570, 580, 590, 600, 610, 620, 630, 790, 910, 920, 930, 950, 960, 970, 980, 1150, 1250, 1260, 1270, 1280, 1290, 1300, 1310, 1320, 1330, 1350, 1360, 1370, 1380, 1390, 1410, 1420, 1430, 1440, 1460, 1470, 1480, 1590, and 1600.

In the old days, a III-A was either 1000 or 5000 Watts Nighttime. A III-B was either 500, 1000, or 5000 Watts Nighttime. A Class III was a Daytime only station or 500, 1000, or 5000 Watts Nighttime. If a station received less than 125 uV/m 10% skywave from any interfering signal, it was a Class III-A. If a station received more than 125 uV/m 10% but less than 200 uV/m 10% skywave from any interfering signal, it was a Class III-B. If it received more than a 200 uV/m 10% interfering signal, it was a Class III.

Many stations operated at less than the 500, 1000, or 5000 Watt nominal power level with a Series Limiting Resistor, if they interfered too much with full power. In later years, in about the 1970s, stations were allowed to turn down the power output without the SLR, and still be licensed as 500, 1000, or 5000 watts, if they met the minimum Class III/Class B efficiency of 175 mV/m @ 1 mile for 1 kW. Many stations are still licensed that way. If they are relicensed, they have to specify the actual power they operate with. That is what you see so many stations now with slightly lower power levels when they move or are otherwise relicensed. Of course, DA's are allowed to operate with 1.081 times the specified power below 50 kW, and 50 kW stations are allowed 1.05 times the power to compensate for power losses in the directional antenna system.

 

[billmich]

and how were 1610 (1620)- 1700 originally considered back in the 80's. Were they to be "regional" channels, or their own special animal?

 

[Schroedingers Cat]

They are considered Regional, but they have a different set of rules, and are designated as Expanded Band. Almost all are nondirectional. None operate with more than 10000 watts. Some now operate with 10000 Watts Night, but are coastal stations which are directional, directed into the ocean so they don't radiate more than the equivalent of 1000 watts nondirectional toward Canada and Mexico.

 

[Ai4i]

The real solution would be an expanded FM band and full power FM stations to replace many AM stations.

People are talking "either-or", that is, to admit channels five and six into the FM band or to maintain them as TV channels for the few stations that would seem to otherwise become homeless. Nobody really favors shared services, but it deserves consideration, at least in the short run. Very few low-band digital TV stations exist and there are vast areas with none, so why not do what is done very successfully on channels 14-20 with land-mobile? The TV stations would be protected on their channels, but once they vacate them, that area would henceforth and forevermore be FM. The overwhelming majority of areas would not have this issue.

 

[gr8oldies]

Other than people who post in places like this, is ANYONE actually considering adding channel 5 and 6 as a 2nd FM band? Never mind the fact that no one, but no one, is buying new radios and the wireless industry wants every frequency it can get

 

[rbrucecarter5]

Other than people who post in places like this, is ANYONE actually considering adding channel 5 and 6 as a 2nd FM band? Never mind the fact that no one, but no one, is buying new radios and the wireless industry wants every frequency it can get

Well said. People didn't buy new radios for HD, they didn't rush out to buy them when the AM band was extended from 160 to 1700, why does anybody think they will buy them for an expanded FM band?

 

[Schroedingers Cat]

Many radios can be switched to get 76-108 MHz. There are also still a lot of TV sound receivers out there. Over a five year simulcast period like with the 1600-1700 kHz Expanded Band, radios and converters would appear to deal with the problem. It's not an ideal situation, but its better than the chaotic situation which will otherwise occur. There are forces who would just like a lot of the AM stations to disappear. 250 watt translators are limited in range but cause widespread interference to established full power services. I think when the {92.3, 93.1,...,107.5} set of big city frequencies start being widely duplicated in markets 50 miles away, and the interference to the fringe service outside the predicted service contours, you will see the big owners start calling for an expanded band. It's just a matter of whose ox is being gored. Smaller markets are always the ones who have been gored. Smaller markets are mainly the ones dealing with the reduction in de facto service areas now. The Old dedicated Class A set of frequencies {92.1, 92.7, 93.5,...,107.1} are heavily interfered with by big city translators because the full power Class A stations are often still stuck at 3 kW, or 6 kW directional, with only 60 dBu protection.That situation will change with all the new translators on the big city set of frequencies. FM full power is certainly still viable, regardless of the AM situation. Long ago, we should have allowed full power stations on directional allotments like Canada has done for decades. You only have to look at what has happened over the last few years in Windsor, ON to see what COULD have been done if they had looked ahead instead of putting allotments in the middle of nowhere under Docket 80-90 and refusing to move them around to serve more people and optimize facilities. The real reason for this was to limit competition, pure and simple. Many of these stations in the middle of nowhere are now simulcasting 100 kW NPR stations where the main signal is totally adequate.

 

[Steve Green NEPA]

WHP Harrisburg here pretty well in the day, from some 50 miles SW as the crow coughs.

One sunset there was WCHS from West Virginia.

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@ CharlestonDXer : Great word depiction there, vis-a-vis WDBO and the Atlanta station.

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@ Cyberdad: I'm kinda new here. Have you asked about reception of day/night stations on the X-band? It was a week or so back, around 9PM, when the radio in the 2008 Sebring was getting at least two stations on each of those frequencies ........

 

[cyberdad]

WHP


@ Cyberdad: I'm kinda new here. Have you asked about reception of day/night stations on the X-band? It was a week or so back, around 9PM, when the radio in the 2008 Sebring was getting at least two stations on each of those frequencies ........

I think I may have done it once or twice, but I really don't remember. I'll do an x-band channel next time.