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AM Stn Groundwave vs Freq, Power & Conductivity

Wow, I've been looking for easy to read charts just like that for groundwave MW conductivity.

Thanks.

I notice the conductivity in the charts only goes up to 8 mS/m. Is there one of those charts for 15, 30, or especially 5000 mS/m?
 
gar fla said:
Is there one of those charts for 15, 30, or especially 5000 mS/m
Click to expand...

The article includes 15mS/m, but not higher. I thought 2/8/15 mS/m represented most of the land area of the US, and that four charts probably were enough to show the points I wanted to make.
 
It shows the point quite well.

One thing I noticed though, is that the chart for 8 mS/m shows a 1 kw station at 600 khz has a limit of 100 miles.

On the east coast of Florida at the beach in Ft. Pierce, I could hear a listenable signal in the middle of the day from 680 WGES in St Pete (only .69 kw) at 135 miles that crosses land of 4 mS/m, 2 mS/m, and some 8 mS/m.

Could the estimates for the charts be on the conservative side?
 
gar fla said:
One thing I noticed though, is that the chart for 8 mS/m shows a 1 kw station at 600 khz has a limit of 100 miles.
Click to expand...

The charts show the 0.5 mV/m contour, which is not the limit at which the signal can be heard on a good radio in an area of low interference. Under very good conditions using a good receiver, a ~50 µV/m AM broadcast signal may be useful (if noisy)

Could the estimates for the charts be on the conservative side?
Click to expand...

The FCC curves on which the charts in this article are based have been shown to be very accurate for the conditions they show, when MW fields are measured by calibrated field intensity meters.
 
Interesting article indeed.

Like gar, I too would be interested in the data for the higher conductivities, including saltwater. I would also be interested in seeing charts for very poor conductivity, like 0.5 and 0.1 mS/m.
I wonder if a low power, high frequency station could do better (to the 0.5mV/m contour) over saltwater than a high power, low frequency station on poor conductivity like Long Island, for example? I recorded brief clips of 500-watt 1290 KZSB and 1kW 1490 KSPE on my barefoot Tecsun PL-606 near the beach in San Diego, CA, 182 miles away - all over salt water except a total of less than a mile. I suspect the signals for a 50kW on 540 (I wish I could see that frequency in the charts, too) wouldn't be as good at that distance with a conductivity of 0.1 mS/m.
It is interesting to note from the charts that 1kW on 1600 does better at 15 mS/m than 50kW at 2 mS/m.

Also I'd be interested in seeing the effects of various other antennas, like a 1/4-wave (and maybe shorter, like 60 or 45 degrees, or even 0.1 wavelength), but especially also a Franklin antenna. Also how much of a difference does the ground system make? I've seen places where development was so close around a tower that I wonder how that station could have any ground radial system at all. I even know of 1020 KTNQ and 1150 KTLK being mounted on the roof of an industrial building east of Los Angeles.
I'd also be interested in seeing data to various other fields for the various frequencies, like 50mV/m, 10mV/m (that's visible for 1600 kHz in figure 4 IIRC), 2 mV/m, 0.1mV/m (I believe my PL-606 is sensitive enough to pull that in when it's not desensed by a nearby (+/-20-30kHz) strong (250+mV/m) signal), and even whatever field a signal would be barely copyable using sound-isolating headphones on a good quality radio with a beverage antenna, whether that be 5 or 1 uV/m or even lower.

Also could I reasonably extrapolate various other power levels, like 250 watts, 100 kW, 500 kW, or even 2.5 MW from the charts?

Or are gar and I the only DXers that might be interested in more data on the weaker signals? ;)
 
There are a large number of combinations of power, frequency, conductivity, radiator height, etc that could be analyzed.

However the purpose of posting the article was not to invite and act on multiple requests for additional comments and analyses, but to show the general relationships of these factors. Hope this will be acceptable to most.
 
Ok, then, how were those charts calculated, and/or based on what existing data? Maybe I could make those calculations myself?
What about data that's "off the charts", though? For example FCC's figure 8 calculator won't let me calculate the field at 1 km for a Franklin antenna, and when I put in 2.5 megawatt power (I know this isn't used in the US, but am aware of the existence of transmitters capable of that) with other criteria within the figure ranges, it exceeds the 4-digit range of the program. (I have found ways around it my quartering the power as necessary, after finding values that will give half the results at 1kW as the specified efficiency for KSTP.) But, also, what about going off-scale on the FCC frequency/conductivity graphs? I was unable to calculate the distance for 2.5 MW with a Franklin antenna (IIRC somewhere upwards of 20-40 V/m @ 1km) at 5 uV/m, for example. (And actually I don't know what the absolute limit under best possible conditions (lowest atmospheric noise, no manmade noise) with the best possible equipment (for example a $10k well-designed MW receiver with a tuned beverage antenna) would be for a signal to be barely detectable on QRSS CW or PSK5 modes, for example.) Is there some data from which I could attempt to make those calculations? Or am I the only one interested in extreme DX? ;)
 
tfcwings said:
I wasn't asking for multiple further analasys, I was just asking what data was it calculated from so I could make an attempt at analyzing it myself.
Click to expand...

That data was identified in my article and in two of my earlier posts in this thread, including the original post.
 
tfcwings, R. Fry has done a nice paper here.

It is not that difficult to use this information, tfcwings, along with the groundwave graphs and other information available at the FCC website and elsewhere online, to answer some of your own questions.

Franklin antennas, and even 5/8 wavelength monopoles, are often not practical particularly at low frequencies. It is becoming increasingly difficult to even get approval for zoning, in addition to the skyrocketing construction costs, and whatever land costs, to even construct a fairly modest AM DA with short 199 foot towers, let alone tall towers and Franklin antennas.

I sugggest having that Stoddart NM-20 professionally refurbished and calibrated, tfcwings. You may be able to find an Electrical Engineering Department at a nearby college to help you out. Maybe they have a newer and better field strength meter. Maybe you could get a position as a research assistant. But you would have to come up with some practical projects and rigorous measurements based in reality, not continuously changing what-ifs.
 
I wish O.G. Villard, Jr. was still alive, tfcwings. He would have been the perfect person for you to talk to. I don't know if the Wikipedia article shows it, but he was an avid AM and SW DXer. His family history is fascinating.

http://en.wikipedia.org/wiki/Oswald_Garrison_Villard,_jr.

He would have pointed you in a practical direction. I was fortunate enough to have talked to him just once on the telephone in the early 1990s. He died in 2004.
 
R. Fry said:
As I posted earlier in this thread, I won't be responding to requests such as yours for multiple further analyses based on my article.
Click to expand...

I'm sorry you took the replies the wrong way.

Like I said, what you posted is what I've been looking for. I just happen to have a specific interest also in saltwater AM DXing and just like tfcwings, I too have an interest in pulling in the weakest possible signals that many DXers don't pay that much attention to.
 
For example FCC's figure 8 calculator won't let me calculate the field at 1 km for a Franklin antenna,
Click to expand...

For more information on Franklin or top loaded antennas, look an article called "An Antenna For Controlling the Nonfading Range of Broadcasting Stations" by Charles L. Jeffers, (from WOAI) published in the proceedings of the I.R.E.
 
gar fla said:
...I too have an interest in pulling in the weakest possible signals that many DXers don't pay that much attention to.
Click to expand...

Maybe you could act on the good advice given in the 2nd paragraph in Reply #11 in this thread, made by Schroedingers Cat?
 
Any ideas what would be a reasonable cost to get a vacuum tube based FIM such as that one serviced?
(Also you replied to gar fla's post, but I assume you were talking to me, as I'm the one that mentioned having a Stoddart NM-20A FIM and SC suggested I get it serviced.)

Also I've been wanting to use the FCC's figure 8 calculator (along with the graphs) to help me figure out some things, but it keeps telling me I entered "0.00" for the frequency. Is there an alternate one I can use until the FCC's is working?
The graphs won't help me figure everything out, though, as some things I'd like to calculate (high power at extreme distances over saltwater for example) are off the scale. Would there be some use for the 4NEC2 program in that case, just set the distance to x km to find the field, for example? (Or is there an option to find the distance to a particular field, rather than the field at a particular distance?)

As for calculating a Franklin, I haven't figured out how to do it for all lengths of "franklins", but I can base it off KSTP St Paul, MN, at least for that size. When the figure 8 calculator was working properly, I had figured out results that would give me 1/2 the value that KSTP has (which is 511.77mV/m @ 1 km for 1 kW), then multiply as necessary. (One thing I was wanting to do was use the Figure 8 calculator (either by going for 1/2 the field, or putting in 200kW, as necessary) to figure out KFBK's field, then find out what its 1 kW RMS field is. I think I've done it before and found KSTP to be stronger per kW, but I wanted to confirm/deny that.)

Also stacker mentioned an article that I would like to read... but the only site I've found via google search that has it is an IEEE site, and I don't have a subscription. (My dad gets IEEE Spectrum in the mail, but I don't have a username/password that I could use for the site.)
 
tfcwings said:
Any ideas what would be a reasonable cost to get a vacuum tube based FIM such as that one serviced?
Click to expand...

Sorry to say, but your posts show a continued tendency to ask others to research and answer your many questions, rather than taking the initiative to do so, yourself.
 
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