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mgh

Range of DF (directional Finding) transmitters

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I am looking for info on the average range of a long range DF transmitters of the early 1940's timeframe. I am going to do some transoceanic flights in a Boeing B314 Clipper. Pilot's plane does have a DF radio, some DF transmitters located at various seaplane basis the clipper flew to, and a sextant gauge can be added.So my plan is to use the sextant until I am within range of the DF transmitter. However the tranmitters that came with the program default to unlimited range, so I need to modify the ranges for the transmitters.

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There are way too many variables preventing a concise answer. Height of DF transmitting antenna above sea level, height of receiving aircraft, transmitter power out, atmospherics, etc. etc. Unlimited range is unrealistic of course, and it seems to me that 200 miles would be more realistic as an average. 250 at the outside.

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AIM chapter 1 has some basics on the service volumes of NDBshttp://www.faa.gov/airports_airtraffic/air...p1/aim0101.htmlSometimes you can use broadcast stations and be able to hear them from thousands of miles away as the sky wave bounces off of the ionosphere. The ground wave is usually disrupted by coastlines and other terrain. If you are speaking about VHF DF similar to what is in use now at FSS stations then it will be much less because of the line of sight restrictions of that wavelength.

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We tried to modify some for a 1934 flight and found that about 195 nm is the farthest range which FS will work with despite any settings in the NDB properties.That is probably related to the default high altitude VOR range and the program not reading the navigation database for farther ranges.If you find a way around that, let me know.

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I have a a 1943 edition of a book called 'Through the Overcast' by Assen Jordanoff which deals with instrument flying in those days.This refers to Department of Commerce transmitters on 950-1500 kHz. Is has diagrams showing that, during the day, the direct ground wave gives reliable reception up to 45 miles: there is then an distance of about 30 miles where the signal is "very erratic or none at all": beyond this the sky wave reflected from the ionosphere gives good reception for a further 500 miles. At night these distances are 65 miles, 135 miles, and 3000 miles respectively.I'm not sure if this helps or hinders!

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