[Lowfer] AMRAD Vertical

[Ed Phillips]

BOB RIESE wrote:
> 
>  Bob
> 
>         The word is coherer, and they are easy to make.  If you're interested
> do a Google search on the word and you'll learn enough to make your
> own.  Basically an insulating tube with metal plugs at the ends and a
> small amount of conductive filings in between.
> 
> I didnt feel like digging out back issues of the OTB and didnt figure the
> spell check
> would have it
> 
> I have played around with one and did get it to work with my Spark
> Transmitter
> but really insensitive. Wanted to be able to do a full demo of Spark
> Technology
> 
> so may things to do
> 
> HAR
> 
> Bob

	I have a home built coherer receiver here excited by a transmitter
comprised of a small model airplane ignition coil, a 1/16" gap, and an
8" vertical antenna.  With the same antenna on the receiver range is
between 20 and 50 feet.  I also have a Japanese-built "Radicon" RC bus
from the late 1950's which uses a coherer receiver and a METER TYPE
sensitive relay.  It also works to between 20 and 50 feet with the
similar transmitter which came with it.  I haven't dismantled the
coherer, but externally it appears as a 5/16" glass tube about 1" long,
with pressed sheet brass caps on each end.  Each time the transmitter is
keyed a motor starts which operates a wheel producing in turn STRAIGHT,
LEFT, RIGHT, STRAIGHT, and OFF.  There were a number of similar toys
(including Robots) made by Radicon at about the same time, but all are
collectors' items now. 

	The coherers I have built consist of 5/32" ID glass tubing with brass
plugs in each end, filed back to an angle of about 45� and with the
closest points sitting at the bottom of the tube and spaced about
3/16".  I have used coin silver, "coin nickel" ( modern 5 cent piece
which is 75# copper and 25# nickel, and finally pure nickel.  The silver
and pure nickel seem to work equally well.  When I sweep the I/V curve
on my curve tracer I observe an "OFF" resistance of at least 1 meg, and
on resistance which is of the order of 100 ohms or less, depending on
how close the spark is.  The trigger voltage is of the order of 4 volts.
For testing I use the trigger generator out of a propane fire starter
with a coule of 2" leads soldered to the terminals and sticking out like
a tiny dipole.  It will operate the gadget from a distance of several
inches.

Ed