"matt weber" wrote in message
news
On Mon, 1 Sep 2003 11:51:53 +0100, "Keith Willshaw"
wrote:

Me-109 has a wingspan roughly the same as a Cessna
at 32 ft
You are missing a very suble, but very important point that is
involved in your argument, and the Chain home argument. Microwave
radars are a relatively late development in WWII.


The US Army SCR-270 could detect aircraft at around 120 miles
out. One such set detected the Pearl Harbor raid 30 minutes before the
attack.

Neither Chain home, or Ship, or airborne radars or the SCR-270 were
microwave radars by any stretch of the imagination for most of WWII.
VHF RADARS relied on much more 'interesting' effects to work.


Quite so


With a Microwave radar, the whole game is RCS, with a VHF radar
(typically 40-70Mhz), if you have to depend upon RCS you are blind.
VHF radar relies on picking a wavelength that produced a resonance
with one or more parts of the airframe, turning them into very
efficient re-radiators, making them appear many many times larger then
the real RCS.

Later in WWII, as Microwave radars became available, chaff was
dispensed as 1/4 wave aluminum foil. It produces such strong
reflections that it blinded the radar. It drove the AGC to the point
where the radar couldn't see anything that wasn't the chaff. The point
is the resonance caused the chaff to appear to have much much larger
RCS then it really had, just as various parts of the airframe did for
VHF radar.



Incorrect

The British used strips of aluminium foil 30cm long by
1.5 cm wide , codename window , to blind the German
radar which was assuredly NOT on microwave frequencies
since they lacked the cavity magnetron


Such technology was often used in towed reflector arrays, where a
few such tuned reflectors towed behind a frigate gave it the radar
signature of an Aircraft carrier! So while you could pick a frequency
that might be able to see a Cessna single well, it would be almost
blind to anything that didn't have similar size, or odd multiple sizes
of the airframe feature being used.

A TBD or a Betty could be seen at about 100 miles, but they are a
whole lot bigger than a Cessna 172


A Cessna Skylane has a wingspan of 35 ft, a TBD had a wingspan of
50ft and an Aichi Val a wingspan of 47.1 ft
Perhaps, but the wing probaly isn't the feature they were relying on.
For a VHF radar you need something that is an odd multiple of 1/4 wave
for it to work well. AT 40Mhz, that is roughly 1.9, 5.7, or 9.5 meters

Guess what 9.7 metres comes out as in feet


The Radar in an F16 in Air to Air mode has a 50% probability of
detecting a 1 m^2 RCS at 40km..


We arent talking about an F-16 radar, we are talking about the
more capable search radars at ground stations.
I think you'd be surprised at just HOW incompetent many search radars
are. Have you ever used one.


You seem to be forgetting that most aircraft radar see only a
narrow cone ahead of them.

I've operated both a Raytheon and a Siemens search radars. The Siemens
was part of a NATO installation, it was 120Kw, and we were about 60nm
from CPH. It had trouble seeing anything smaller than a D9 at that
range, and the doppler speed information at that range wasn't real
good, +/- about 80kt...

So now our range has gone from not seeing light aircraft
at all to 60nm

Keith