On Sun, 20 Feb 2005 10:18:25 -0500, Buck wrote:

On Fri, 18 Feb 2005 18:21:07 -0600, "Crazy George"
wrote:

The initial question was set in the WW2 time period, I believe.

I started the topic. It was set in WW2 because I see so much about
RDF at that time. i realize it has to have improved by now but the
heart of the question is 'since it was possible to be accurate then,
why can't hams accurately do it today?'

I am thoroughly enjoying this thread.

There is really two types of DF. Long haul and close in. The close in
type which generally uses some sort of null loop from a mobile
platform (such as a car or on foot) is what is generally used in "fox
hunting" types of transmitter hunts by hams and other hobbists.
By extension, the military also use some of this close in technique
from tactical aircraft although the technology is different.

Long haul, such as was employed in WW II for sub hunting in the
Atlantic was done from fixed shore facilities for the most part
which exchanged their lines of bearings via a dedicated secure
network.

Close in DF is accurate only in the sense that the hunter can usually
move in close to the target to the point that they can actually see
the antenna.

Long Haul DF cannot pinpoint a target. Long haul DF stations have
known error tolerances and so-call "fixes" are stated with circular or
elliptical errors of probabilities. So one might DF a transmitter
operating in the Atlantic from shore stations around the perimeter of
the Atlantic. The fix will be stated with some degree of tolerance
such as there is a 90% chance the target is within an ellipse 100
miles long and 50 miles wide and a 10% chance it is within a 15 by 5
miles area within that larger circle. This is of course still many
hundreds or even thousands of sqare miles to hunt for a target. I do
not know what technology the Allies used during WW II for their HFDF
or what sort of accuracy they achieved.

In a WW II scenario, it would be an important intelligence fact if
one could discern if a target was near Bermuda or if it was near the
Azores. Then a destroyer or subchaser or small carrier with aircraft
would have to be dispatched to try to find it if it were on the
surface. Allied sub hunting was successful because German doctrine
called for frequent situation reports from submarines to shore
commands in France and Germany.

US submarine operations in the Pacific were more successful in a
defensive perspective since they usually operated with a doctrine of
radio silence and only rarely sent messages to shore station or to
each other. It must be remembered that WW II era subs generally
operated on the surface and submerged mostly for attack or self
protection. The German sub commanders were in essence victims of
Doenitz' tendency to micromanage and they sustained casualty rates of
70% or greater. US sub forces by comparison had casualty rates of 15%
which was still among the highest among US forces. Germany had roughly
four or five times as many submarines as did the US.

[Folks unfamiliar with WW II history must also note that the US had
almost no sub forces in the Atlantic since Germany had only a very
small surface Navy and almost no coastal or open ocean shipping. A sub
of that era was a poor platform to wage war against another submarine.
Japan, being an island, was dependant upon ocean shipping for supplies
and so was more of a natural target for anti-shipping submarine
operations. US subs of course also attacked combatants, but many of
those combatants were escorts for shipping convoys. Virtually all US
submarines operated in the Pacific Theater. The Brits did have some
submarine operations in the Atlantic.]


Jon W3JT
Thank you to ALL that have replied.

Buck
N4PGW