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Ground System Importance

Yes it works. It helped that the (former) owner's father was touring the site one day and needed to use the bathroom. A working growler was much appreciated. Also a kitchen and shower. All left over from the attended site times. You could argue that a working toilet would be required by the ADA if the engineer had something like Crohn's Disease or irritable bowel. Plus the drain field will keep the building’s ground system wet in this dry climate.
 
Ron Rackley did a study on this a few years ago, Basically, he found that going from virtually no ground system to a perfect (120 degree radial) ground system affected the radiated field by about 25% To put this in perspective, doubling your power increases your field by 40%. Therefore, the ground system affects things by about 1.5 db or so.
 
I'm guessing that the question of ground system importance can be answered with two words: ground conductivity. If you're in an area with good ground conductivity, a good ground system is going to be more important. If you're in an area with poor ground conductivity, not so much.

Then there are the rumors of teapot AMs strapping their ground system to neighboring railroad tracks, and getting a signal to go a loooooooong ways farther than predicted, but very directional...
 
SirRoxalot said:
If you're in an area with good ground conductivity, a good ground system is going to be more important. If you're in an area with poor ground conductivity, not so much.
Click to expand...

For those who want to maximize groundwave coverage area regardless of ground conductivity, another POV is that regardless of ground conductivity beyond where the radials are buried, the goal should be to radiate as much of the applied power as possible. For a given frequency, TPO and radiator height, and using 120 1/4-wave buried radials as an r-f ground -- once that signal is launched there is nothing (practical) that can be done to improve the ground wave signal levels received from that site.

In 1937 George Brown et al showed that such systems launched groundwave fields which, when measured close to the monopole were within a few percent of the maximum possible for a perfect radiator over a perfect (zero-loss) ground plane.

//
 
SirRoxalot said:
If you're in an area with good ground conductivity, a good ground system is going to be more important. If you're
Click to expand...

I find that counter-intuitive.

There is anecdotal evidence, however, that a good salt-water path for a few miles in front of a significant pattern lobe contributes to a good skywave signal in that direction. The extreme example is probably WBZ. Yes, the RMS signal is equivalent to ~100 kW because of the half-wave towers and the signal to the west is equal to ~200 kW because of the cardioid pattern, but the six or so miles of salt water to the west of the Tx site before you hit land is responsible for yet another boost in the effective skywave signal strength. Unfortunately, no curves or equations in the FCC regs take this last effect into account, but if you think about the the effect of the salt water on the vertical radiation pattern, intutively, I think you'd have to agree that the salt water has gotta help.
 
Dan, I agree with you on WBZ considering its empirical skywave to be superior. Before all the new stations on 1030, I used to get WBZ occasionally at HIGH SOLAR NOON in the winter in Michigan. There were no other stations like WABC or WCAU coming in at the time. I wish I had a FI meter that I didn't have to borrow in my possession, or I'd be able to tell you how much signal I had compared to predicted.

I totally agree with the 100 kW RMS "ERP" of 0.5+ lambda towers. I think the most logical reference is the Class B minimum efficiency of 282 mV/m @ 1 kW @ 1 km, not 300. Many stations still operate at minimum effieciency of Class Bs with reduced power, even though they would have to state the actual power if relicensed. Even Class A KOA apparently still uses a series a series limiting resistor, as I suspect several other directional Class As may use at night, or power below 50000 watts.
 
Schroedingers Cat said:
KOA uses a 207.8 degree monopole, and has an efficiency of 362.1 mV/m @ 1 kW @ 1 km. This is equivalent the the minimum efficiency for a Class A.
Click to expand...

But those two statements (207.8 degrees and 362.1 mV/m/kW @ 1 km) are inconsistent with each other. A radiator that tall would have an efficiency of about 420 mV/m/kW @ 1 km. Even with a seriously substandard ground system, the efficiency of a radiator that tall would exceed 362.1 mV/m/kW @ 1 km.

Here's how I understand the situation: US treaties with other Western Hemisphere nations (most importantly, Mexico in this case) limit KOA's radiation efficiency to the Class A minimum. Other treaties REQUIRE US Class A AMs to operate with an antenna-input power of 50 kW. I know of only one exception to this rule in the US: KNZR. AFAIK, the Bakersfield 1560 is explicitly exempted from the 50 kW requirement.

Given the conflicting requirements, the only resolution appears to be to dissipate part of the transmitter output power in a series resistor. I have never understood why KOA doesn't operate during daylight hours with the resistor shorted out and at night with the resistor in place. I don't think the higher RMS field during the daytime would have any international implications, though it might do so during critical hours.
 
Dan wrote:

"But those two statements (207.8 degrees and 362.1 mV/m/kW @ 1 km) are inconsistent with each other. A radiator that tall would have an efficiency of about 420 mV/m/kW @ 1 km. Even with a seriously substandard ground system, the efficiency of a radiator that tall would exceed 362.1 mV/m/kW @ 1 km."

My point exactly. Oldtimers who remember the 225 mV/m per kW @ 1 MILE would see it immediately if they saw 225, realizing that that would correspond to a radiator some 10% less than 180 degrees, which is the Class minimum height requirement according to that particular graph.
 
Don’t think the limits KOA had prior to the revised treaties in the 80’s is in effect anymore. Same reasons the protection of class A's in the US was relaxed.

According to KOA they do not have a resistor in line.

But hey, the FCC database is never wrong, is it? They still have an AUX license of ours in there that the license was turned in - deleted 9 years ago.

This is fun reading.
Final Acts, of the Regional Administrative MF Broadcasting Conference (Region 2) Rio de Janeiro, 1981
http://www.tzsawyer.com/pdf/rj81.pdf
 
If KOA doesn't use a resistor then either:

1) they reduce the power to the antenna and have minimum Class A efficiency or

2) they put 50000 watts to the antenna and have an efficiency consistent with the 207.8 degree tower and the FCC Query result is wrong, both the resistor comment and the efficiency.

I've seen other records that I suspect were messed up like that.
 
There is a thread on the Indiana board about the former 1400 WROZ Evansville. I copy the comment here since it is of relevance of this thread:

"Before the move to the river, the tower and transmitter were on top of the old YMCA building downtown. The copper strap ground system ran down the sides of the building, and then was quietly bonded to the water main below ground which helped the signal considerably. As a kid up in Princeton, I could copy them day and night. But after they moved out to the river, the signal level was never the same. OK during the day, but a no-show at night."
 
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