Mid-Atlantic AM DX

[rfry]

I'd like to see a chart for sea water conductivity of 5,000 mS/m.

Here in table format are some spot values for the distances to the 0.5 mV/m groundwave fields for a path conductivity of 5,000 mS/m using a 1/2-wave vertical, series-fed monopole transmit antenna with a 2-ohm connection to the ground plane:

Freq (kHz) Power (kW) Distance (miles)
600 1 249
1000 1 225
1600 1 209

600 50 514
1000 50 449
1600 50 406

I take it those color lines represent the limit of listenable 'distant' coverage and not actual 'fringe' distances.

The plotted fields of 0.5 mV/m (and sometimes less) can provide fairly noise-free reception on a decent AM receiver, depending on the local r-f noise level and interference from co- and adjacent-channel signals.

A theoretical field of 25 mV/m or more might be needed to provide a quiet, competitive groundwave signal in major metro areas with high r-f noise levels.

RF

 

[cyberdad]

I used to say that if the planet needed an enema, it would be administered via Guayaquil. I particularly enjoyed the week or so of the "cricket invasion" where bugs that were not really crickets would cover the walls, your nose and clothes, the streets. Unfortunately, the major ad agencies and one of my stations were there, so I went once a week for about 8 years.

I don't go back; places where I have been ejected by soldiers with big rifles do not appeal to me very much. Still, my oldest daughter and her family live there, amid the horrible economy and the "equality is achieved via universal poverty" president.

Great story, David. I used to call on some industrial companies in "funky" areas of Detroit and Cleveland. Steel gates, armed security guards, etc. But your experience definitely tops that!

 

[rfry]

Also would this article contain useful information (formulas, for example) on how to calculate surface wave fields over distances, as affected by ground conductivity and frequency (hopefully I could set a "reference" of 100 mV/m @ 1 km for example)?

Yes, it contains much useful information with many references to other good resource material. Just study and apply that information correctly and you will be able to calculate for yourself a lot of what you ask here.

Others may want to use the groundwave propagation charts for the MW broadcast band published by the FCC, or for some applications use NEC software.

RF

 

[gar hi]

I'd like to see a chart for sea water conductivity of 5,000 mS/m.

Here in table format are some spot values for the distances to the 0.5 mV/m groundwave fields for a path conductivity of 5,000 mS/m using a 1/2-wave vertical, series-fed monopole transmit antenn mS/ma with a 2-ohm connection to the ground plane:

Freq (kHz) Power (kW) Distance (miles)
600 1 249
1000 1 225
1600 1 209

600 50 514
1000 50 449
1600 50 406

Those numbers still seem very conservative unless we're talking about a local quality signal only in which case they would be spot on.

A 1 kw station on 800 khz from 465 miles on saltwater.

http://www.youtube.com/watch?v=djAgueBwbt0

Here's a 50 kw station on 640 khz on a 280 mile land path of 8 mS/m and a sea path of about 20 miles.

http://www.youtube.com/watch?v=yNzZw2aS_34

Maybe the proximity to the ocean could of enhanced the signal more too.

 

[rfry]

Those numbers still seem very conservative unless we're talking about a local quality signal only in which case they would be spot on.

We are approaching this differently. My purpose was to show the range for the stated conditions that would provide reasonably quiet program audio output from an average indoor AM radio receiver -- something that an average person would want to listen to for an extended period of time. The listening quality in the clips you posted don't really meet that standard, and use equipment that the average listener would not have.

WSHO in New Orleans is directional, and radiates about 1.2 kW toward Dunedin, FL. According to the FCC propagation curves for 800 kHz and 5,000 mS/m, WSHO should produce a groundwave field of about 60 microvolts/meter on the Gulf shoreline at Dunedin.

That is enough to be detected with good equipment and good receiving conditions, but probably not a quiet enough signal for anyone to want to listen to for very long.

RF

 

[gar hi]

We are approaching this differently. My purpose was to show the range for the stated conditions that would provide reasonably quiet program audio output from an average indoor AM radio receiver -- something that an average person would want to listen to for an extended period of time. The listening quality in the clips you posted don't really meet that standard, and use equipment that the average listener would not have.

OK, I see what you're talking about.

Like I said, I was thinking those distances listed would apply to a pretty good signal and not just an audible signal period.

 

[davideduardo]

We are approaching this differently. My purpose was to show the range for the stated conditions that would provide reasonably quiet program audio output from an average indoor AM radio receiver -- something that an average person would want to listen to for an extended period of time.

Good point. I've approached this from a real world perspective by analyzing the predicted signal strength for Arbitron diary reported listening in a variety of top 100 markets over about a decade. Since the diary method showed in home and at work listening, and the ZIP code of both, it was a question of determining the signal strengths where different percentages of location-specific listening occurred.

For AMs, in top 20 metros where there are consistently high noise levels, somewhere between 90% and 95% of listening occurred inside the 10 mV/m contour. In a number of markets, 15 mV/m was the limiting factor for nearly all listening.

In other words, at home or at work, where about 70% of all listening happens, we need at least a 10 mV/m signal or more to get listeners to use that signal. Where there is less signal, listeners do not tune in, even if the station is very well used in the stronger signal areas.

This is also why one of the most significant providers of radio financial and valuation data only qualifies about 160 AM stations in the top 100 markets as "viable" which seems to mean they cover at least 80% of the market population day and night with a usable signal.

As you said, being able to hear or occasionally DX a station is not a measure of the usable coverage of a station.

 

[crainbebo]

Best I've done on saltwater was KWRO 630 Coquile, OR (300 mi+) at Pacific Beach this summer, mixing w/ KCIS. Unfortunaly, that was close to sunset, so I'm more than half sure that was early skywave.

-crainbebo

 

[gar hi]

Take it from someone who is fascinated with saltwater path DXing, I wouldn't underestimate a 300 mile catch like that.

After reading your post, I was looked at the maps and was thinking that if you were able to go to a beach somewhere as far north as possible on the most northwestern tip of Washington state, you should be able to get 980 KINS from Eureka, Ca during the middle of the day, as it's on virtually a complete saltwater path.

As far as I know, there are no locals on that frequency or the adjacent frequencies.

 

[crainbebo]

Sorry, but CKNW may cause trouble up there...was in Sekiu, WA in 2006 and had KAPS 660 Mount Vernon among other NW WA and Van Island stations, CKMO 900 the best.

-crainbebo