[Milsurplus] Re: Very Interesting WWII German Transmitter

[David Stinson]

----- Original Message ----- 
From: "Hue Miller" <kargo_cult at msn.com>


> Dave, how is the motor geared down to the very low RPM for the
> key wheel?

Don't know, Hue.  That whole assembly, 
except for the end of the DC motor
and a small opening for lubrication, is sealed.
Take a look at:
 http://home.netcom.com/~arc5/s23b/001.jpg
The motor is the long, silver thing at the bottom left
with the screw-contacts on each side of it.
Imagine a cylinder.  Stand it on it's end, then cut it down the long axis.
You have a rod that is "half-round."  
The flat side faces down in this photo
and the code wheel axle extends perpendicular to the flat side.
You can see brown edge of the code wheel, with the "K" cut,
at the bottom right of the motor.  
If you look at the left side of the "half round" casing, you can see
a removeable cover.  If you remove one screw, this cover comes off
and gives access to the end of the motor with electrical connections
and a lubrication hole.  The fit is snug and there's no way to see
what's past the end of the motor.  The rest of the case is sealed.
It sounds like a normal clock-work kind of mechanism.
The motor has markings for "+" and "-", but nothing to indicate 
operating voltage.

> ....The case
> is an organic material, not synthetic, and it could be fashioned
> from less-strategic material by not highly trained slaves.

Build quality looks very much like it was done by 
someone with little concern for quality control.
The connections to the latching relay were just
"tack soldered," rather than wrapped around the
contact eyelets.  This one may have survived because,
when I got it, one of the low-voltage contact wires had
come loose.  So it may have gone into the "bad" pile
and never got fixed.

> One thing puzzles me, DFing this thing in the broadcast band
> might be a challenge, wouldn't it? And the frequency, you
> couldn't really depend on it coming up on a tightly controlled
> frequency, seeing as the trail wire capacitance is a good part
> of the tuned circuit.

You're right.  Given the frequency of operation and
the uncertainty of the final frequency of the transmitter,
a "DF" purpose doesn't make sense.
According to what I've been able to discover,
it really wasn't designed for DFing; it went on-line when 
the V-1 got within 30 km of the target, one would assume
to let the Germans know that at least some of them were
getting through.  In contrast, the T-13 transmitter in 
the U.S. JB-1 copy worked at 3-6 MC xtal control
 and was designed as a DFing aid.

The frequency of the thing is very quirky, indeed.
I fired it up today with 300 volts on the B+.  
It will just barely oscillate at  that potential, 
and takes a long time to warm up.
It came up on 915 KC, but that varied by how close 
you were standing.  It has come up as high as 960 KC.

I think having it in the broadcast band was actually 
a pretty smart idea.
BCB carriers provide the "BFO," 
and you don't have to worry about
tuning to an exact frequency; you'd hear the beat note 
against the BCB station using wide AM bandwidth.

One thing- The latching relay is marked for 24 VDC 
and will not pull in at less than 19-20 volts.  
One in ten of the V-1s was fitted 
with one of  these things, meaning at least one in ten 
had an electrical system.
This would mean the need for both 24 and 12 volt systems,
assuming they were running the LS50 at the speced 12 volts.
Documentation for a V-1 "control box," 
indicates a 24 volt electrical system.
A dual-voltage, 24 and 12 volt system means a lot of extra weight; 
a dual-voltage dynamotor (24 volts in, 12 and 1000 volts out) 
would be really heavy for something like a V-1.

The transmitter was supposed to turn on 
during the last 30 kilometers of the flight.  
30 kms equals about 18 miles, which is about 
3 minutes flying time for a V-1.
What are the odds that they decided they could get away with 
running the LS50 at 24 volts for the three minutes 
it was going to operate?
The filament in the tube certainly looks "beefy."
Here's one factor that might support that:  the keying speed.
Run at 12 volts, the keyer sends a dash for a full minute,
then sends "K" with the "dah" lasting 3 seconds 
and the "dit" lasting one second.
At that keying speed, 
given the 3 minutes this transmitter had to live,
you'd get only two IDs from it before "BOOM."
That doesn't make sense.  
If the whole transmitter actually runs on 24 volts,
you'd get several IDs before the big plunge.

73 Dave AB5S