gar fla said:
I'm just saying that if you search through the literature, there's a general agreement on ocean conductivity and skip and the maximum distance of one single skip on medium wave frequencies and that's about 500 miles.
There may be agreement via repetition in DX circles. However, I cited one of many studies that take into account low level longer distance paths.
One thing that has barely been studied is higher latitude blanking of local groundwave signals by subtropical stations which may be single path or even ducting caused by auroral conditions. An example is the total absence of WTAM 20 miles from its transmitter with a 10 kw Venezuelan 100% readable an hour or so after sunset in Cleveland in September. Similarly, east west paths in the tropics are notoriously poor, but little study of this has been done.
There's a reason these hard core DXers go to coastal areas in order to pick up transatlantic stations and that's because just as is the case with a ground wave, the saltwater also provides much less signal loss with reflection of sky waves as well.
MW DXers go to areas with little local noise or interference. If you erect a beverage antenna in Newfounland, you go to the coast for a number of reasons.
First, you if you want to get SA and Africa, you go to the southern coast. Second, you go where it is flat, so you can lay out at least one if not more 1000 foot long (minimum) wires. Since you need to put in a support, like snow fence slats, you need fairly soft earth. So the coastline in many places is where you would find this.
Second, you want to get away from noise, so on a coastal area at least 180 degrees is clear of power lines, which is fine since beverages are directional off one end.
Third, you want to go where thre are few local stations. Again, a coast guarantees that there are no stations in the way of your target. Some of the Scandinavian DX locations where DXpeditions go are landlocked, but have all the other conditions for good reception, particularly transpolar.
That's the only thing that can explain the vast difference I've noticed between reception of the NYC stations on Florida's east coast as opposed to here at night.
You are comparing a North South with an East West path, one of which is about two and a half times longer.
And the transmitter's proximity to the water is irrelevant because WABC's stick is located well inland in north Jersey and, as shown in the video I provided, they have a much better signal too at night on our east coast.
WABC's site is relatively close to salt water... the Argentinian station used for part of the tests was totally land in one direction, and reasonably close to the River Plate in the direction of a European path.
As I said, there is considerable study on propagation(you can find an IEEE paper summarizing about 8 studies via search), including an extensive study where long, medium and short range skywave of specific stations was monitored over long periods of time. The conclusion was that the "takeoff" being in proximity to a large body of salt water was more important than the actual path, irrespective of how many skips might be involved; the whole purpose of the study was to isolate issues of distance and focus on the location of reception and or transmission.
NYC is under 1100 miles from Miami, while LA is 2500 miles. Beyond that, we have the issues of the NY-MIA path being near N/S and having essentially no interference to the east, while the NY LA path is closer to E/W with interference on all sides all the way.
Now if you're talking daytime reception of distant stations, then yes, the transmitter's proximity to the water is a crucial factor. That's why WNBC and WCBS are the only NYC stations that would have a chance of reaching the east coast of Florida in the daytime.
Inland salt marshes work out as well as being footwet. I've only built one, on 660, that was near a tidal estuary and about 10 km inland from the estuary and the thing talked much better daytime than we ever expected. Similarly, I worked with a 100 kw AM on 710 that was also on marshy land many kilometers from the same Argentinian delta area, and it performed as well as stations closer to the river.
