Long Wave and Short Wave Radios

[gwendy730]

Hi guys!

I'd like to ask a few questions on WWII radio sets. I've been reading Battle for Manila, and there was some mention there (not a direct quote):

Sometime in 1944, the Voice of Freedom had been picked up by long wave radio sets. Radio sets with short wave capabilities had been banned by the Japanese since 1941, which means that the signals must be coming somewhere close to Manila. (Leyte. The radiobroadcast was of Macarthur's return)

From this information, am I right to assume that short wave radios have the ability to pick up signals outside the country while long wave can only get those within the country?

I also read about the Japanese "re-conditioning" radio sets so it won't be able to pick up frequencies from the Allies. Can one "un-recondition" a radio set? And what did WWII radios, particularly those used by guerillas, look like?

Thanks for reading!

[Doc]

Generally, you are right-- short wave transmissions tend to have a longer range than long and medium wave transmissions. That's why I can pick up shortwave radio stations from around the world, but AM usually is limited to the next country over. As to re-conditioning sets-- many early radio sets still in use in the WW2 period were tuned using crystals. You needed the right frequency crystal to receive on that frequency. So, simply removing all the crystals except for those you want people to be able to receive on could easily prevent them from receiving enemy transmissions. I don't know if this is what was done in the case you refer to, but I suspect it is. Doc

[morse1001]

There are not much can be added to what Doc has said.

[the_historian]

I'm sure it's possible to build an AM receiver for SW/LW without actually needing crystals; it's powered by the incoming radiation, so doesn't need an on/off switch. You just disconnect the aerial. Bear in mind that I haven't actually built one for about 30 years, so feel free to correct me; got a great little book somewhere tells you exactly how to do it, but haven't the faintest idea where I put it.

[PeterG]

Originally Posted by Doc

short wave transmissions tend to have a longer range than long and medium wave transmissions.

many early radio sets still in use in the WW2 period were tuned using crystals.

Hi Doc

I never saw a crystal set in use, they were very rapidly phased out in the mid 1920s. I remember our 5 valve Bush wireless set arriving in the mid 1930s, and we had a valve set before that. The same was true of friends and relatives, so far as I recall. This was in England, but it was the same in Italy in WW2, the only sets I saw there were valve sets.

The distance covered by radio waves depends on the power of the transmitter, not on the frequency.

Long waves were the very first to be used and they transmit around the world. Now long waves are used mainly for navigation and for time signals. Very high waves are line-of-sight only, that's why TV transmitters are set as high as possible. It is medium waves which typically cover only a few hundred miles, unless bounced. A good ploy is to bounce them off the moon.

Some excellent info here radio wave propagation

Peter

[Kyt]

Crystal sets were used during the war:

BBC - WW2 People's War - Crystal Sets

BBC - WW2 People's War - England and the English were never far from our minds

Foxhole radio - Bizarre Labs

[morse1001]

Originally Posted by the_historian

I'm sure it's possible to build an AM receiver for SW/LW without actually needing crystals; it's powered by the incoming radiation, so doesn't need an on/off switch. You just disconnect the aerial. Bear in mind that I haven't actually built one for about 30 years, so feel free to correct me; got a great little book somewhere tells you exactly how to do it, but haven't the faintest idea where I put it.

POWs used to build shortwave receviers using thin wire as the aerial and someones filling as a power source. The speaker was a razor blade which vibrated.

[Kyt]

Originally Posted by morse1001

POWs used to build shortwave receviers using thin wire as the aerial and someones filling as a power source. The speaker was a razor blade which vibrated.

From:
Foxhole radio - Bizarre Labs
POW Radio

Prisoners of war during WWII had to improvise from whatever bits of junk they could scrounge in order to build a radio. One type of detector used a small piece of coke, which was a derivative of coal often used in heating stoves. The piece of coke used was small, about the size of a pea. A small board was used and a depression was cut into it near one end to hold the coke. A screw and, if available, a screw cup were used to hold the coke in place. A wire lead to the receiver was run from this to the coil/aerial (see Set 5).
A foot or so (30cm) of steel wire (guitar wire, piano wire, etc.) was wound around a pencil, long nail, or similar, leaving about one inch (25 mm) unwound at each end. The wire should be somewhat springy.A second screw and screw cup is set about 3 inches (75 mm) from the first. Attached by this screw are one end of the steel wire spring and a second lead, which is connected to one lead of the headphones or earphones (if anyone has any information on how earphones from these sets may have been improvised, I would like to hear about it). The steel spring wire was then stretched so that it just rested on the coke. After much adjusting of the point of contact on the coke and the tension of the wire, some strong stations would have been received.
If the POW was lucky enough to scrounge a variable capacitor, the set could possibly receive more frequencies.




Here's a another great description of a POW radio (it was hidden away in my link above)

R G Wells: Index

[von Poop]

Originally Posted by Kyt

Here's another great description of a POW radio (it was hidden away in my link above)

Disguised as a box of toothpowder no doubt...

[PeterG]

Originally Posted by Kyt

Crystal sets were used during the war

Yes, you can make one now if you wish. This is quite different from commercial cat's whisker sets. They were phased out in the 1920s, valve sets spread like wildfire and crystal sets were soon forgotten.

Peter