power change question

[firepoint525]

Okay, I'm a layman when it comes to engineering issues, so please respond to me in layman terms.

Okay, it's late afternoon, and I'm broadcasting on my local AM station, and it's getting dark, and thus close to time to reduce power, or sign off if it's a daytime-only station. (I've done both).

It seems to me that when it is close to time to power down, that my station's signal (even though I may be authorized by the FCC to stay on at daytime power for a few minutes longer) might already be interfering with the signals of stations to the east of me, where it may already be dark, or to the north of me, where it gets dark earlier and faster, particularly in the winter time.

I know that we adjust our power-down times once a month, but it seems that in the early part of the month, I am powering down just before sunset, whereas by the end of the month, I may actually be on at full power for a few minutes after my local sunset. (This obviously applies to months in which the days get shorter, like September, for example.)

So how do stations prevent interfering with each other's signals, when everyone's sunset is not at the same time, and similar situations in the morning, when everyone's local sunrise comes at a different time? It seems like mass confusion would reign over the airwaves right around sunrise (dawn) and sunset (dusk) every day.

 

[Goat Rodeo Cowboy]

It is not an exact science. The bureacracy decided that setting times one month at a time was practical and enforceable, having a daily variation in the time: NOT PRACTICAL.

If you will nose around some FCC files and other sources you will learn one more term: CRITICAL HOURS. You will find that some stations have to reduce power... maybe as much as two hours earlier that their sign-off or their reduction to NIGHT TIME power. A number of stations have THREE power levels: Daytime. Critical Hours. Night time.

There is not much, if anything stations can do near those power-change times to be nice to each other. Every DAY is different depending on the weather and other conditions that affect the skywave bounce..... WHEN it begins to happen, and WHAT it does with signals when it happens.

 

[radioboy]

Also, the power change time is based on the average of the different sunset times for any given month. This
is the way that the times are figured.

There's an AM station here that has SIX different power levels. It ranges from 5,000 watts daytime to 18 watts
at night. That was not always the case with this station, which began as a daytimer. It's on 1410 AM. It's
funny that with 6 power levels, none of them are "critical hours" changes!

 

[stormy01]

Also, the power change time is based on the average of the different sunset times for any given month. This
is the way that the times are figured.

There's an AM station here that has SIX different power levels. It ranges from 5,000 watts daytime to 18 watts
at night. That was not always the case with this station, which began as a daytimer. It's on 1410 AM. It's
funny that with 6 power levels, none of them are "critical hours" changes!

So what are the 6 power levels, and when do these changes take effect throughout the day? That would probably frustrate all but the listeners more than a few miles away.

 

[DanStrassberg]

There's an AM station here that has SIX different power levels. That was not always the case with this station, which began as a daytimer. It's funny that with 6 power levels, none of them are "critical hours" changes!

So what are the 6 power levels, and when do these changes take effect throughout the day? That would probably frustrate all but the listeners more than a few miles away.

Besides the daytime power level (5 kW) and a nighttime power level (18W), there could be a pre-sunrise power (6:00AM to local sunrise in the winter) and two post-sunset levels (first hour after sunset; second hour after sunset). That gets you to five levels. But the post-sunset levels CAN very from month to month. All it would take would be one of the two levels being assigned two values--say one value in mid-winter; the other the rest of the year, and you'd have your six levels. That's NOT necessarily how the FCC assigned the levels for this particular station, but I COULD have nailed it--or not. There are virtually limitless possibilities and, with the month-by-month variations, six levels are by no means the largest possible number. One thing is sure, though: There are no Class A AMs on 1410. Class As are the only class of stations that require co-channel stations to use different power and/or patterns during Critical Hours. So CH is not a consideration for this 1410 station.

Thank goodness for computer (or microcontroller) based automation systems. Only practical way to keep track of large numbers of power levels.

 

[DanStrassberg]

I forgot to mention that there is a little-known feature of the average sunrise/sunset times. As everyone knows, the average sunrise and sunset times are rounded to the nearest quarter hour. The feature I'm about to describe applies to certain stations that operate from separate day and night transmitter sites. It is possible for such a station to have its day site in a location where, say, the rounded-off average sunrise time in some months is 15 minutes later than the night site's rounded-off average sunrise time in the same months. Without some special provision, this situation would force the station to go off the air for 15 minutes right around sunrise. So the FCC took mercy on the affected stations and makes the rounded-off "average" sunrise (and/or sunset, as the case may be) times for both sites agree in all months. As has already been said in this thread, the times are not an exact science. Bear in mind, that the situation I described actually does exist at one or more stations and it can be the result of the difference in the NOT-rounded-off calulated average sunrise and/or sunset times at the two sites differing in some months by as little as 1 second!

 

[mgpt6]

Multiple Towers, Phasors, different power levels....Reason Enough for FCC to use Ch 5-6 TV to expanded FM , to move AMs there except Class 1 50kw to FM. One tower ,One power level, same directional pattern 24/7.
Need I say more.

 

[firepoint525]

It is not an exact science. The bureacracy decided that setting times one month at a time was practical and enforceable, having a daily variation in the time: NOT PRACTICAL.

I remember a former coworker who snarkily commented that the sunrise and sunset times must change by 15-30 minutes from the last day of one month to the first day of the next month! And you are right, minute-by-minute daily variations would not be practical. As it was, once we memorized the power change times, here comes a new month, and we had to learn the new month's power change times.

If you will nose around some FCC files and other sources you will learn one more term: CRITICAL HOURS. You will find that some stations have to reduce power... maybe as much as two hours earlier that their sign-off or their reduction to NIGHT TIME power. A number of stations have THREE power levels: Daytime. Critical Hours. Night time.

My former station, after getting a power increase, had to incrementally increase power like that in the morning, per agreement with a station in Alabama! (The stepped-up power increase was eventually phased out.)

 

[firepoint525]

Also, the power change time is based on the average of the different sunset times for any given month. This is the way that the times are figured. There's an AM station here that has SIX different power levels. It ranges from 5,000 watts daytime to 18 watts at night. That was not always the case with this station, which began as a daytimer. It's on 1410 AM. It's funny that with 6 power levels, none of them are "critical hours" changes!

This same station that I just mentioned above (in my last reply) also had (at least for a while) an incremental decrease in power in the evening, at least in the summer months. I believe this was because the former GM had a beef with the host of the hispanic program (the station was part-time Spanish, primarily in the evening), and I believe he instituted this incremental power drop to get back at the host of the program over something. What, I never knew.

 

[firepoint525]

Multiple Towers, Phasors, different power levels....Reason Enough for FCC to use Ch 5-6 TV to expanded FM , to move AMs there except Class 1 50kw to FM. One tower ,One power level, same directional pattern 24/7.
Need I say more.

Best solution yet!

 

[boiseengineer]

Reality hits stations quite hard with 50 KW stations allowed on nearly all but the graveyard (Class D) frequencies. I know of a little kilowatt (during the day) that has a co-channel 50 KW only 350 miles away. It gets blasted as soon as the 50 powers up in the morning for an hour or more after sunrise, and again in the afternoon for an hour or more before the 50 shuts down.

 

[Goat Rodeo Cowboy]

Of course, that works both ways. When I wake up in the mornings I like to pick up WGN (50KW) out of Chicago till daylight kills their signal. But a couple of months ago I got jarred out of bed when a much lower powered daytimer up in North Carolina suddenly came blasting through the static and fading of WGN.... with morning vespers from some North Carolina Church.

I am obviously not in the primary listening area of EITHER station.... so who is interfering with whom at that point?

 

[boiseengineer]

Another way to KILL AM radio. When a stations night 5 mV/m NIF and day 2 mV/m contour is shrunk to 25 mV/m for a good deal of morning and afternoon drive time in the winter months.

 

[DanStrassberg]

... the graveyard (Class D) frequencies...

You mean Class C. Class Cs are the former Class IVs (nearly all on 1230, 1240, 1340, 1400, 1450, and 1490). Class Ds are the former Class IIDs and IIIDs. Some Class Ds are still limited to daytime-only operation. However, most have been granted some night authority with powers of less than the equivalent of 250W into a ~54-degree antenna (RMS inverse-distance field of less than 140.85 mV/m @ 1 km) and no nighttime protection from interfering signals.

 

[Bengalsfan]

Then you get stations that get to raise power at night! WPAD in Paducah Kentucky powers down to a kilowatt sunset local time from 10kW daytime. Then, sunset Bakersfield CA, WPAD gets to raise power to 5kW when KNZR goes directional with a null to the east.

 

[DanStrassberg]

Then you get stations that get to raise power at night! WPAD in Paducah Kentucky powers down to a kilowatt sunset local time from 10kW daytime. Then, sunset Bakersfield CA, WPAD gets to raise power to 5kW when KNZR goes directional with a null to the east.

1560 and 1530 are special cases (1080 was too--until a couple of months ago). 1110 is kind of the reverse special case. On 1530, WCKY (if those are the calls du jour) stays on day pattern (ND, I believe) until Sacramento CA sunset. On 1560, WEQW stays on day pattern until Bakersfield CA sunset. On 1080, WTIC used to stay on day pattern (ND) until Dallas TX sunset. On 1110, KFAB switches to day pattern (ND) at Charlotte NC sunrise. As far as I know, the Paducah 1560's switch to low power from local sunset until Bakersfiled sunset is not directly related to KNZR. Rather, the power reduction is to protect WQEW's 0.5 mV/m 50% skywave contour during the period when it is nighttime in Paducah and WQEW is operating with its day pattern after sunset in New York.

Based on the FCC's position in the WTIC case, I suspect that the use of day facilities at night by the other former Class IB AMs that still do it is not likely to last much longer. When those Class A licenses are modified, Paducah will be able to switch directly from day pattern/power to night pattern/power.