[Milsurplus] Foxhole Radios

[Robert Nickels]

On 7/21/2010 3:58 PM, Ralph Cameron wrote:
> the Blue Blade which enabled it to rectify. As a detector
> this was sometimes used with a safety pin for contact, other times
> pencil lead was used.
>    

The ones I used to make as a kid came from a Popular Science book, which 
I still have.   It says the original GI design called for the use of a 
"blue blade" and safety-pin cat whisker, but engineers who copied it 
later found that adding a section of pencil lead to act as the actual 
cat whisker produced a "decided increase in volume".   Since my dad used 
an electric razor, I was stuck using the modern single-edged "safety" 
razor blade,  but never had any difficulty picking up the local BC 
station as well as my storebought "Remco" crystal radio did.   (As many 
hams have learned, it often doesn't take much to get rectification!)   
The article does suggest scraping a few light scratches across the blade 
and avoiding the area where the manufacturers name is printed to help 
find the most sensitive spots.  This radio uses a 2 1/2" diameter coil 
with 120 turns of #28 or #30 wire.

The article attributes the design of the "foxhole radio receiver" to 
Army Lieutenant. M. L. Rupert, who was attached to an infantry outfit 
while serving on the Anzio beachhead in Italy.     I don't know if or 
when it might have been published in the magazine, but it appears in the 
book titled "Boys Fun Book of Things to Make and Do" and is copyright 1945.

73, Bob W9RAN