Is there a one-stop source of the exact hours as AM station is permitted to operate and what power levels are permitted? There's the license, then there's the PSRA & PSSA Correspondence Letters. What leads me to this is a certain station (not in my state) that has signed off year round at 7PM local time for at least 15 years, yet the FCC Correspondence Letter shows PSSA of 1 watt for the first hour & 0.0 watts for the last hour. The power they operate with between local sunset & 7PM is quite low. In that time zone, 7PM local is more than 2 hours past local sunset in the winter. Either that station is operating in violation of it's authorization, or there's another piece of the puzzle that my inquiring mind hasn't located.
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Accurate AM Power Level Figures
- Thread starter BobOnTheJob
- Start date
Can you give us the call letters?
As far as I know, these figures aren't available to the general public. The PSRA and PSSA letters that were set out on February 28, 2007 were all proven to contain flawed data, and were subsequently ordered to be disregarded. Stations were instructed to revert to the power levels on the authorizations they previously had, which aren't published anywhere.
At a power level of one watt, I wouldn't think that they would interfere with anyone.
Some 50kw stations radiate more than one watt when they operate into their dummy load.
Some 50kw stations radiate more than one watt when they operate into their dummy load.
Sure...it could hardly be a secret what time a commercial AM station actually is on the air. WLBH 1170 Mattoon,IL.frankberry said:
BobOnTheJob said:
1W sounds low. This station is in the "corridor" behind the patterns of WWVA and whatever the OKlahoma 1170 is called this week. I assume that Mattoon is in southern IL, but I would be surprised if it weren't more than 400 miles from both WWVA and the OK station and outside of the protected 0.5 mV/m 50% skywave contours of both. At that distance, radiation of at least four or five watts toward each of them might be permitted. In fact, a real nighttime authorization doesn't sound out of the question. OTOH. there are a lot of surprises on the low side, too.
Mattoon is almost exactly 400 miles from WWVA and more than 500 from Oklahoma City. Usually if a station has night power of any amount at all, it's shown as a Night license, but this one shows nothing of the sort and it shows 0 watts PSSA. If they had a night license, one would think they'd let it run all night. Maybe they had something based on sunset in Oklahoma City at one time?
Dan...what you said got me thinking...that station has been there for a very long time. If they have a sign off time based on sunset in Oklahoma, and they may operate 2 hours past that with PSSA, they may have picked the earliest sign off time of the year & standardized on that. I can't locate a copy of their Daytime license, but it would sure be interesting to see if they have a non-standard sign off time like WJJD/1160 Chicago had long ago (sunset at KSL).DanStrassberg said:
BobOnTheJob said:
Local sunset at a co-channel Class A is no longer a non-standard signoff time, though it is not very common. Here's how I understand the rules; if you find errors, please correct them! Usually, only one Class A is involved. If the Class D station is east of the Class A and the Class D's transmitter is located outside of the Class A's protected 0.5 mV/m 50% skywave contour, the Class D is technically eligible to operate full time. As a practical matter, protection of the Class A's 0.5 mV/m 50% skywave contour is not feasible for Class Ds that are closer than about 150 miles from the protected contour. For ND Class As running 50 kW-U with 195-degree antennas, the protected skywave contour lies roughly 500 miles from the transmitter. The interfering 0.025 mV/m 10% skywave contour of an ND Class A with a 90-degree antenna running about 5W at night would be ~150 miles from the Class D's Tx or ~650 miles from the Class A. If the Class A is directional (as are both of those on 1170) and you are "behind" both patterns (as I guess Mattoon must be), the Class D to operate at night must be at least ~250 miles from each Class A. More distance is better. I'm pretty sure that there ARE full timers (Class Bs) on 1170 in the corridor between WV and OK. The problem with the Mattoon station becoming a Class B is cost. First off, its NIF must cover at least 80% of the population of the CoL. Second, its night RMS inverse-distance field must exceed 141 mV/m @ 1km. Third, there are all of the costs and hassles of siting, designing, getting local approvals for, and building a night array. Also, since I believe that, on 1170, there are Class Bs in the corridor, they would require protection. Seems to me that the most practical approach would be to determine whether ND night operation as a Class D at low power but higher than what they have been using might be allowed. Remember, about 20 years ago (give or take) the FCC changed the formulas for determining nighttime skywave coverage. That change reduced the nominal protected coverage radius of 50-kW ND Class As from ~750 miles to ~500 miles. It is not impossible that Mattoon could be granted more night power than it has been using.
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