Hi, do you think a crystal radio located in central Italy would have been able to pick up Radio London during WWII? In other words, could a radio using a galena crystal pick up the signal of a radio 900 miles away?

The first transatlantic radio transmissions used even less sensitive coherer detectors, so yeah, it's possible depending on a lot of factors.

Thank you very much.
Would you be able to list some of these factors?

Noise from electric devises, ionospheric conditions, time of day, and interferance are a few factors.

Norm

Very true, but the first transmissions were in Morse code, not voice (AM). Much easier to get information from Morse.

However, a Belgian friend of mine (now deceased) said that he and his father could receive the BBC during WW II, using a crystal receiver that was built in to a hollowed-out book.

During wartime, there is much less competition from other broadcasters, so less interference.

Rich

Super interesting, thank you very much, Rich!

That was shortwaves presumably? And rather high power to reach as far as possible and as many people as possible for propaganda purposes. Probably a good long antenna was needed in many areas to hear such a distance. Purely dependent on the amount of energy available from the passing signals for a crystal radio. So the longer the wire the more energy up to a point. I suppose at night a very powerful MW signal could propagate a long ways to a crystal set too.

With a crystal set made from modern materials , an 80 foot inverted L antenna and WWII sound powered headphones 1000 miles is listenable most evenings .St. Louis to Denver ,St. Louis to NY city and when the local 550 KSTL is off the air for maintenance 530KHZ in the Caribbean can be heard .

Thank you very much Mark and wazz!

I agree this is true when you are dealing with a BFO impressed upon a signal, but I am not so sure that Morse in a crystal detector would be any easier to copy.
But way back in those times of a Coher I think the Morse would have been spark gap.

Tikker...

https://en.wikipedia.org/wiki/Tikker

There are several crystal radio DX reception examples on the internet. Probably the most important factors are the antenna (proper length and tuning), and grounding. Also detector efficiency, tuned tank Q and proper matching of impedances, earphone sensitivity, and last but not least transmitter power and propagation conditions make or break successful reception.
The theory behind estimating the possibility of the reception is called the Friis transmission formula. It's very theoritical and probably unrealistic for terrestial propagation, but if you punch the numbers in (say 1MHz, 50kW, 0dB antenna gain on both sides) then in an ideal case a receiver 900 miles away would get 50uW of power out of the transmission, which is more than adequate for a good volume reception in a crystal radio. Of course there's no way to estimate all the various factors without knowing the exact circumstances, but the point is that the reception is possible in theory, in an ideal case, with the above numbers.

Thank you very much! This is great

Search for Fox Hole Radio on the internet.
The G.I.s used them in WW2

There was a lot of information on crystal radios on The Radio Board Forum, though it looks like it might be abandoned.