AM NIGHTIME SERVICE QUESTION.

[radiotower40]

I hope this is the right place to post this. I have a rather unusual question, I was hoping someone could help me
with. The question is about AM daytimer's. I have a couple of stations in mind when I ask this, stations such as
WAIT AM 850 in Crystal Lake, Il. and WCPT AM 820 in Chicago(Willow Springs, Il.) WCPT has already been issued
a CP for a six tower array in Joliet, Il. , with a power of 1.5kw, for nightime service. These stations both have PSSA's.
The question I have is, would stations such as these be able to operate at night, with very low power levels from their
daytime facility's. I have looked at the CDBS search page on the FCC website, and I can find PSSA's and PSRA's,
for these and other stations, it states that they are not allowed any nightime power. I know WAIT is outside of KOA's
protected nightime skywave coverage. Is there any source to find out what power they would be allowed at night,
if they ever requested it? I know they would be in the"flea power" range, but, there are quite a few stations out there,
that are allowed 1 or 2 watts, that were previously listed as not being able to operate after sunset. Sorry about the long
question, this is just something I have been curious about for some time.

 

[BobOnTheJob]

I posed a similar question in the past & came up dry. All I was looking for was a public record of the PSSA & PSRA powers of existing stations. I have often wondered what the non-d PSSA & PSRA would be on a station I take care of. After all, if the daytime antenna points the signal at the night limiting station, then a non-directional antenna would--in theory--allow better night power/coverage. Its a shame that the FCC didn't calculate the powers both directionally & non-directionally for each station. Or at least issue a monitor point that could be measured during the day with non-d operation & allow non-d night operation as long as that monitor point stays within limits. This may be one where the consultants have us in their grips...they know the answer to our question, but they rarely talk without compensation.

 

[radiotower40]

I posed a similar question in the past & came up dry. All I was looking for was a public record of the PSSA & PSRA powers of existing stations. I have often wondered what the non-d PSSA & PSRA would be on a station I take care of. After all, if the daytime antenna points the signal at the night limiting station, then a non-directional antenna would--in theory--allow better night power/coverage. Its a shame that the FCC didn't calculate the powers both directionally & non-directionally for each station. Or at least issue a monitor point that could be measured during the day with non-d operation & allow non-d night operation as long as that monitor point stays within limits. This may be one where the consultants have us in their grips...they know the answer to our question, but they rarely talk without compensation.

Bob, I don't know if you ever went to the FCC's CDBS search page, but if you go there you can find PRSA's and PSSA's
for any station without nightime service. The direct link is http://fjallfoss.fcc.gov/prod/cdbs/pubacc/prod/sta_sear.htm
When you get there scroll down and enter the call sign of the station, then scroll 2 lines down and click on AM STATION,
then go to the bottom of the page and click on the "SUBMIT STATION SEARCH" link. When you get there hit the "CLICK FOR DETAILS" link. Then scroll to the bottom and click on "VIEW CORRESPONDENCE FOLDER", when you get there you will see
the link for PSSA"s and PRSA's. I know that sounds like a lot but it is the easiest way to find the info. Keep in mind these
are computer generated calculations, and a lot of stations have higher power levels for pre and post sun operation.
I think your right about the consultant's though, they are probably the only one's that have the answer we want.

 

[BobOnTheJob]

I posed a similar question in the past & came up dry. All I was looking for was a public record of the PSSA & PSRA powers of existing stations. I have often wondered what the non-d PSSA & PSRA would be on a station I take care of. After all, if the daytime antenna points the signal at the night limiting station, then a non-directional antenna would--in theory--allow better night power/coverage. Its a shame that the FCC didn't calculate the powers both directionally & non-directionally for each station. Or at least issue a monitor point that could be measured during the day with non-d operation & allow non-d night operation as long as that monitor point stays within limits. This may be one where the consultants have us in their grips...they know the answer to our question, but they rarely talk without compensation.

Bob, I don't know if you ever went to the FCC's CDBS search page, but if you go there you can find PRSA's and PSSA's
for any station without nightime service. The direct link is http://fjallfoss.fcc.gov/prod/cdbs/pubacc/prod/sta_sear.htm
When you get there scroll down and enter the call sign of the station, then scroll 2 lines down and click on AM STATION,
then go to the bottom of the page and click on the "SUBMIT STATION SEARCH" link. When you get there hit the "CLICK FOR DETAILS" link. Then scroll to the bottom and click on "VIEW CORRESPONDENCE FOLDER", when you get there you will see
the link for PSSA"s and PRSA's. I know that sounds like a lot but it is the easiest way to find the info. Keep in mind these
are computer generated calculations, and a lot of stations have higher power levels for pre and post sun operation.
I think your right about the consultant's though, they are probably the only one's that have the answer we want.

Those are the recently recalculated letters that went out. I believe I was looking for the info prior to that, in particular for a station that had never used it's night power or PSSA/PSRA...we were trying to find the information & in that station's case, it was necessary for the FCC to calculate the power again. As you pointed out, the PSSA/PSRA are now available. The next question is how do we find the "offered" night power of those stations that didn't accept it in the past is/was? Any ideas along those lines?

 

[radiotower40]

No, unfortunately I don't. It's seems as if we are in the same boat. I am going to keep searching though. I have not been
able to find this info no matter how I tried. That is why I finally posted it here. I will keep on searching though. I have tried
speaking with people at the FCC in the past, but, got the phone runaround. Maybe I'll give that another shot. If I am able
to find anything, I will make sure to let you know.

 

[NHRadio]

If you live near those stations you could always look at their license in the public file.

The next question is how do we find the "offered" night power of those stations that didn't accept it in the past is/was? Any ideas along those lines?

 

[boiseengineer]

I remember a past discussion about the original PSA PSSA authorizations. Seems even the FCC doesn't have those records anymore. Probably lost in the conversion from the old databases. That yellowing mouse eaten piece of paper that was posted at the transmitter would have been the only proof the station even had PSA PSSA authorization. Loose that and the FCC would have to use the newly figured powers.

 

[BobOnTheJob]

I remember a past discussion about the original PSA PSSA authorizations. Seems even the FCC doesn't have those records anymore. Probably lost in the conversion from the old databases. That yellowing mouse eaten piece of paper that was posted at the transmitter would have been the only proof the station even had PSA PSSA authorization. Loose that and the FCC would have to use the newly figured powers.

Sadly, the newly figured powers supercede the original ones. One of my stations had it's 80 watt PSRA cut to 13 watts...ouch.

 

[techie2]

I remember a past discussion about the original PSA PSSA authorizations. Seems even the FCC doesn't have those records anymore. Probably lost in the conversion from the old databases. That yellowing mouse eaten piece of paper that was posted at the transmitter would have been the only proof the station even had PSA PSSA authorization. Loose that and the FCC would have to use the newly figured powers.

Sadly, the newly figured powers supercede the original ones. One of my stations had it's 80 watt PSRA cut to 13 watts...ouch.

I thought the newly figured powers were rescinded because they made a bunch of mistakes in the calculations, and they have yet to issue the corrected numbers.

 

[BobOnTheJob]

In the case of the 80 watt to 13 watt PSRA change, the FCC contact said we had to abide by the 13 watts due to a Canadian clear channel issue. That was issued when we requested PSRA numbers as a new transmitter made them possible for the first time. They were actually issued about a year before the ones in the correspondence folder.

 

[semoochie]

Not to answer the question but I believe nighttime power for such stations is based on the second hour of PSSA.

 

[jboyd]

Let's face the facts...the FCC is thru with daytimers....those early/ Late permits are a joke....what does 13...50...65 watts mean? If you sell it the client is almost certainly disappointed. Why do you think thay do not accept applications from daytimers anymore? I will run mine until I cannot support it any more. After all, when I came to this market 31 years ago, it was all I had! Sad....JBI

 

[Tom Wells]

Let's face the facts...the FCC is thru with daytimers....those early/ Late permits are a joke....what does 13...50...65 watts mean? If you sell it the client is almost certainly disappointed. Why do you think thay do not accept applications from daytimers anymore? I will run mine until I cannot support it any more. After all, when I came to this market 31 years ago, it was all I had! Sad....JBI

Such low powers were able to serve when the pre/post service was authorized, as most radios of the day had either a tube-pentagrid converter with REAL RF
gain or even a preselector stage as in the case of vitrually ALL auto radios back then. Switching mode power supplies weren't around then, nor many dimmers.
Modern radios are deaf as a post on AM because they are deliberately trying to desensitize them to noise, and now they are only about one half the senstivity of what was standard in the 70's. With average modern cheap radios, it's likely not worth the effort.

With the FCC letting the "uniintended radiators" situation go as they have, such low powers can only serve listeners who are magically or by their efforts, in a clean enough location to hear you, and then they need a GE Superadio, or some old thing with meaningful sensitivity/selectivity/loop antenna.
I'd favor fixing the noise problem first. There's no excuse for it, all these noisy designs should have never received pt 15 cert.
Can anyone explain why the FCC never made any regulatory efforts to preserve the environment, now badly polluted as surely as we've ever done to any environment. The other option is to make more RF to overcome noise, and tends to escalate the problem.

 

[DanStrassberg]

The question is about AM daytimer's. I have a couple of stations in mind when I ask this, stations such as
WAIT AM 850 in Crystal Lake, Il. and WCPT AM 820 in Chicago(Willow Springs, Il.) WCPT has already been issued
a CP for a six tower array in Joliet, Il. , with a power of 1.5kw, for nightime service.

The answer to the question about WCPT seems easier than the answer for WAIT. It seems almost completely obvious that the FCC OUGHT to authorize a nondirectional night power from WCPT's day site that would send no more skywave toward WBAP's protected contour (0.5 mV/m 50% skywave) than does the 1.5 kW CP night service would at its radiation minimum. If you assume that the vertical radiation patterns of both antenna systems are the same (probably not true but not too far from true), you would be allowed whatever power would give you an inverse-distance field of 2.0 mV/m @ 1 km. If my calculation is correct--and it may not be--that works out to all of 47 microwatts(!). Given WBAP's huge signal in Chicagoland, that does not sound like enough power to make the station audible at the end of its ground radials. Actually, you might be allowed a bit more power because WCPT's day site is 30 miles further from WBAP than is WCPT's CP night site.

As f0r WAIT, it seem as though you should do a skosh better. First off, WAIT is a few miles further from KOA than WCPT is from WBAP. Also, KOA's inverse-distance field is right at the Class A minimum of 362.2 mV/m/kW @ 1 km, whereas WBAP's field is 397.4 mV/m/kW @ 1 km. That's a significant difference and it means that KOA's calculated 0.5 mV/m 50% skywave contour is a few miles further from Crystal Lake than WBAP's contour is from WCPT.

It would be better, of course, if WCPT's night CP were on the air and you knew the pattern augmentations. Almost certainly, the augmented value would allow somewhat more than 2.0 mV/m at the radiation minimum. But lacking the augmentation info (and assuming that I did not make a mistake in my calculation), you would probably be restricted to something not too much greater than the absurdly low power I calculated.

 

[rfry]

If my calculation is correct--and it may not be--that works out to all of 47 microwatts(!)

Maybe some typos there, Dan. A 1/4-wave monopole needs ~0.0407 watts (40.7 milliwatts) of applied power in order to generate a 2 mV/m inverse distance groundwave field at a radius of 1 km, over a perfect ground plane.

The equation I used (adapted from eq. 15 on page 27-7 of REFERENCE DATA FOR RADIO ENGINEERS) is

E = SQRT(98.4*P)/R

where

E = Field intensity, V/m
P = Power, watts
R = Distance, meters

Still not very much power, though.

//

 

[DanStrassberg]

Maybe some typos there, Dan. A 1/4-wave monopole needs ~0.0407 watts (40.7 milliwatts) of applied power in order to generate a 2 mV/m inverse distance groundwave field at a radius of 1 km, over a perfect ground plane.

Thanks, Richard. Indeed! I repeated my calculation, which was based on WCPT's licensed day facility, whose tower, though a lot taller than 1/4 wavelength, must have a substandard ground system (easily understandable, given the location). That tower has an efficiency of 292 mV/m/kW @ 1 km. Using that value, I got 0.000047 kW or 0.047W, which, I think, would agree with your slightly lower number if I had used the somewhat higher efficieny of a standard 1/4-wavelength radiator with a standard ground system.

Now there may be yet another small saving grace. I believe that the FCC does not require augmentation of the field on any radial for which the measued signal strength exceeds the predicted value by less than 20%. If that is correct, then the power could probably be 44% higher than the predicted 47 mW. In other words, almost 68 mW. I remain unconvinced, however, that such a low power would be useful even for test purposes given the strength of the competing signal from WBAP.

 

[BobOnTheJob]

Maybe some typos there, Dan. A 1/4-wave monopole needs ~0.0407 watts (40.7 milliwatts) of applied power in order to generate a 2 mV/m inverse distance groundwave field at a radius of 1 km, over a perfect ground plane.

Thanks, Richard. Indeed! I repeated my calculation, which was based on WCPT's licensed day facility, whose tower, though a lot taller than 1/4 wavelength, must have a substandard ground system (easily understandable, given the location). That tower has an efficiency of 292 mV/m/kW @ 1 km. Using that value, I got 0.000047 kW or 0.047W, which, I think, would agree with your slightly lower number if I had used the somewhat higher efficieny of a standard 1/4-wavelength radiator with a standard ground system.

Now there may be yet another small saving grace. I believe that the FCC does not require augmentation of the field on any radial for which the measued signal strength exceeds the predicted value by less than 20%. If that is correct, then the power could probably be 44% higher than the predicted 47 mW. In other words, almost 68 mW. I remain unconvinced, however, that such a low power would be useful even for test purposes given the strength of the competing signal from WBAP.

I want to see the RF Ammeter used to accurately measure either power.

 

[littlejohn]

Boonton made it - was called an 'RF Millivolter" and you used a shunt.

 

[rfry]

That tower has an efficiency of 292 mV/m/kW @ 1 km. Using that value, I got 0.000047 kW or 0.047W, which, I think, would agree with your slightly lower number if I had used the somewhat higher efficiency of a standard 1/4-wavelength radiator with a standard ground system.

Correct. As a rough check for my post I had used a perfect 1/4-wave monopole with a zero ohm connection to r-f ground; inverse distance field = 313.7 mV/m at 1 km for 1 kW.

An efficiency of 292 mV/m is about 93.1% of that, and the amount of power reduction connected with that efficiency is 0.931^2 = 0.8667 X.

Your power value of 0.047 watts x 0.8667 = 0.0407 watts, which is the value I gave.

I like it when the numbers work out.

//

 

[radiotower40]

Thanks for the answers guys! I must admit I am not much of an engineer, I found your math and calculations
to be very impressive and interesting. You opened a whole new world to me, being on the sales and marketing
side. I must admit that I'm shocked that the power would be that low. I would have guessed they would have been
in the .006kw to .020kw range. I would be very grateful if you could direct me to some sites to find out more information
on the calculations you did, as well as sites that would help me learn more about directional antenna systems. These are
definitely things I would love to learn more about. Years ago I wish I would have listened to my algebra teacher .

On the subject of WCPT 820 AM's tower setup. The tower is located in back of a store front(that used to be home to
WXRT/WSCR), between a crowded city street and an alley. In fact you can drive down the alley and practically reach
out and touch it. It is a very tall tower, as it used to be home to graveyard station WSBC AM 1240. It is still used as
a aux. tower for them. It is mounted to the roof of the one story building. I imagine the grounding isn't quite as good
as would be, if it was located in a more open area. How much effect does this type of setup have on a stations signal?