I have this question that has been bugging me for years. How can the FM signals on the Empire, most are around 1300+ feet with very low power 6kw, have the same coverage as midwest/southwest signals utilizing 100kw at 1500 feet. In the antenna farm in Philly most signals are much more powerful with almost the same height but with same coverage.
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empire signals
- Thread starter Gunsmoke
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This might help answer your question.
https://www.fcc.gov/media/radio/fm-station-classes
Many of the FM stations in New York City are licensed as Class 'B' stations. The maximum antenna height for 50kW is 150 meters. Above that height, the power must be reduced so as to keep the coverage area the same as it would be with the 50kW/150 meters combination.
100kW Class 'C' stations have a far larger coverage area.
https://www.fcc.gov/media/radio/fm-station-classes
Many of the FM stations in New York City are licensed as Class 'B' stations. The maximum antenna height for 50kW is 150 meters. Above that height, the power must be reduced so as to keep the coverage area the same as it would be with the 50kW/150 meters combination.
100kW Class 'C' stations have a far larger coverage area.
The Philly antenna farm has HAAT numbers in the 800 to 900 foot range, not the 1300 feet of the ESB. So power is much higher.
However, the class Cs (and C0/C1/C2/C3) are protected from interference only to their 60 dBu contours. In class B territory, Bs are protected to the 54 dBu, the only class of station protected that far out.
With the explosion of translators and LPFMs and drop-ins, fewer and few stations get to enjoy interference-free service very far beyond those protected contours anymore. That extra 6 dB of protected signal for the Bs makes a difference for signals like the Empire FMs.
With the explosion of translators and LPFMs and drop-ins, fewer and few stations get to enjoy interference-free service very far beyond those protected contours anymore. That extra 6 dB of protected signal for the Bs makes a difference for signals like the Empire FMs.
@ Gunsmoke : I once had to explain to the governing board about a signal from a proposed LPFM in their town.
I know squatto about electronics.
I used the analogy of an empty ice-cream cone -- just the cracker part of it -- sitting on a desk like a small teepee. If you affix a wee light bulb at the top (the point of it), then the usable illumination on the ground is, after all, a circle of light.
I asked who on the board had the least knowledge of electronics (beside me, lol) what would happen if you picked up the teepee a few inches. The board member, a gal, was first with the answer! She said that the circle of light would get bigger on the table. So the light bulb at the top would have to be dimmer.
It's wasn't a * perfect * analogy, but everyone on the board 'got it'. And my buddies who send me to the meeting got their LPFM license
I know squatto about electronics.
I used the analogy of an empty ice-cream cone -- just the cracker part of it -- sitting on a desk like a small teepee. If you affix a wee light bulb at the top (the point of it), then the usable illumination on the ground is, after all, a circle of light.
I asked who on the board had the least knowledge of electronics (beside me, lol) what would happen if you picked up the teepee a few inches. The board member, a gal, was first with the answer! She said that the circle of light would get bigger on the table. So the light bulb at the top would have to be dimmer.
It's wasn't a * perfect * analogy, but everyone on the board 'got it'. And my buddies who send me to the meeting got their LPFM license
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Light is a good analogy to use because higher frequency radio signals behave similar to light. I once used the same analogy at a radio station board meeting and everyone got it!
If WRFF is 12kw @1000' and WNEW is 6kw @ 1300' with same coverage, meaning the 6kw less power at WNEW gives the same coverage, the extra 300 feet on the empire can have the same coverage at 6kw as the 12kw WRFF. Also just checking at random a midwest flamethrower KGOR Omaha which is 110kw @ 1200' only gets out 10 more miles than WNEW 50 vs 60 miles local signal strength. 110kw vs 6kw and 1200' vs 1300' for an extra 10 miles and this is over flat ground not an ubanized area, am I missing something.
It's the difference in coverage between 54 dBu and 60 dBu that Mr. Fybush describes above. I plugged in your figures on the FCC FM/TV propagation curves function https://www.fcc.gov/media/radio/fm-and-tv-propagation-curves and the results come out like this: 110 kW @ 360 meters (approximately 1200 ft) with 60 dBu signal strength = 78.2 km. That's the protected signal strength in most of the US except the heavily populated states generally north of the OHio and east of the Missississppi, plus most of California. Now, let's take the 6 kW at 360 meters and place it in New York. Because we use the 54 dBu protection standards for the Northeast, it goes out to about 62 km. IF we placed our 6 kW at 360 meters in Nebraska, the protection standard goes up to 60 dBu and the resulting contour goes down to 49 km.
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Now, a question for Mr. Fybush. If you're an FM broadcaster in the Northeast operating a typical class B, which would you rather have: 50 kW at 150 meters protected out to the 54 dBu = 65 km, or would you lobby for a change in the FCC rules to permit your class B to operate at 100 kW at 214 meters protected out to the 60 dBu = 65 km?
But in Nebraska and much of Class C territory, there may not be a co-channel station for hundreds of miles anyway, making the 60 dBu "protection" a moot point.
I randomly picked one of the Class C facilities in Omaha, KISO, 82kW at 1050 ft AGL. The 54 dBu contour for KISO is about 65 miles.
Its nearest full-power co-channel to the west, KINI, is in central South Dakota. And is 270 miles straight line distance to that facility.
There is a co-channel translator in Kearney, NE with the full 250 watts. But Kearney is still 100 miles beyond the 54 dBu contour of KISO and therefore extremely unlikely to limit its reception - only the limits of the receiver will do that in the open plains of Nebraska.
I randomly picked one of the Class C facilities in Omaha, KISO, 82kW at 1050 ft AGL. The 54 dBu contour for KISO is about 65 miles.
Its nearest full-power co-channel to the west, KINI, is in central South Dakota. And is 270 miles straight line distance to that facility.
There is a co-channel translator in Kearney, NE with the full 250 watts. But Kearney is still 100 miles beyond the 54 dBu contour of KISO and therefore extremely unlikely to limit its reception - only the limits of the receiver will do that in the open plains of Nebraska.
Once you get out to Nebraska, there's just more gravy to go around. There might (repeat, might) be enough gravy to go around in Nebraska that nearly every AM station under 5 kW could get at least a full class A FM. Might not be a good trade if you're KXSP 590 Omaha but there might be a fair number of AMs that might jump on that trade.
Keep in mind that the usefulness of the lower field strength signal is somewhat limited.
The practical limit for indoor (work, home), listening is arounnd 65 dbu. 95% of indoor listening has been calculated to be in that contour, and 80% is in the 70 dbu.
A weaker signal is usable in cars, but you do get to a point of diminishing returns as the signal gets weaker and weaker in the fringe areas.
NY and Philadelphia also have co-channel issues with 101.1 and 100.3 - It becomes a real mess between the two cities.
That piqued my curiosity...WRNB Media (Philly) operates at 17 kW at 263 m HAAT with a directional antenna. Relative field toward NYC is .65 = 7.2 kW which is what I used in plugging through the computations on the FCC FM curves tool. With these curves, interference is defined where the service grade of station A is 20 dBu greater than the interference grade of station B. WRNB is station A, WHTZ Newark (NYC) is station B with 6 kW at 415 m HAAT non directional.
I'm guessing this computation would be more elegantly solved by calculus (?) but I'm a plugger not a mathematician*, so I plugged in some values till the math worked out to with a few kilometers.
WRNB (station A) 7.2 kW 263m HAAT 45 dBu(50,10) = 93.6 km
WHTZ (station B) 6 kW 415m HAAT 65 dBu (50,50) = 41.8 km
Add the two distances above, it's 135.4 km which is close to the 133 km actual distance between the two stations. ( My calculation assumed perfectly flat terrain in all directions, where to be more precise you'd use the radial HAAT in the azimuths between the two stations. To be MORE precise, we'd use a Longley-Rice calculation but the old FCC curves are good enough for illustration.)
I'm assuming the two stations have a mutual interference agreement that allows them to encroach each other a lot closer than usual. 65 dBu appears to be the point where WRNB begins to suffer interference from WHTZ.
Following with what Mr. Eduardo said above, having a stronger signal closer to the trasnmitter is more valuable than having an interference free signal further out. After all, how well does a 54 dBu service grade signal penetrate into buildings?
then there is WJBR, if you stand under their tower you could almost touch their 6 bay. I guess their 50kw at that low height gives them strength. Two questions, If they went to 1300 feet with 6kw ala Empire signals, from that same location off Naamans road, would they have the same coverage, or does brute power win over actual antenna height.
@ Gunsmoke: I'm guessing that there always will be the debate among radio engineers vis-a-vis height versus power.
'Height' gets you out father with less wattage (and perhaps more importantly, it's cheaper to do with lower wattage). There are more holes in the signal -- the whoosh-whoosh-whoosh picket fence effect in the car.
'Power' better gets your station to penetrate office walls, homes, billboards, foliage, human bones, etc.
'Height' gets you out father with less wattage (and perhaps more importantly, it's cheaper to do with lower wattage). There are more holes in the signal -- the whoosh-whoosh-whoosh picket fence effect in the car.
'Power' better gets your station to penetrate office walls, homes, billboards, foliage, human bones, etc.
One advantage to lower power/higher tower is interference reduction. While 50 kW at 150 meters and 6 kW at 400 meters provides the same 65 km circle per the FCC FM service(50,50) curves at 54 dBu, the co-channel interference (50,10) curves at 20 dBu down, 34 dBu the results are 171 km for 50 kW/150m and 151 km for 6 kW/400m.
Plus, I'm guessing that a 50 kW/150 meters outside of a heavily developed downtown core with tall building would experience some serious shadowing as the signal passes through the downtown area.
Plus, I'm guessing that a 50 kW/150 meters outside of a heavily developed downtown core with tall building would experience some serious shadowing as the signal passes through the downtown area.
Quick Question, it seems the only empire signals I can receive here in Philly are 106.7 the strongest then 103.5. If most of the signals are the same height, power and spacing, outside of 101.1 and 100.3, why do I only receive these two. Do they have greater coverage for some reason then the others, which never come in...
Nope.
Especially on crowded RF turf like the Northeast Corridor, coverage is about more than just raw power/height. It's usually limited by other interfering signals. In this case, the culprits are likely the HD carriers of the first-adjacent Philly Bs. 92.5 wipes out 92.3, 93.3 wipes out 93.1, 94.1 wipes out 93.9, etc. 103.5 doesn't have a Philly B on the first-adjacent, though WPRB's upper HD should create some degree of interference. 106.7 has 106.9 for a neighbor, and EMF's not running HD there, are they? Other special cases are 107.5 (with WBYN co-channel as a semi-local) and 99.5 (with WJBR co-channel as a semi-local).
I'd think WQHT should pop in now and again on 97.1, since there's nothing on the adjacent channel in Philly except translators.
I'm shocked you can pick up WKTU at 103.5! When I'm in Middlesex County NJ (Edison, East Brunswick areas) I have difficulty! 103.3 WPRB makes it nearly impossible.
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