Date: Tue, 24 Aug 2010 08:29:53 -0400
From: Brad Sparks
Subject: October 22, 1957;     Wiesbaden AFB,  West Germany (BBU): RADCAT

October 22, 1957; Wiesbaden AB, West Germany (BBU)
At 2:00 p.m. local time, a target was picked up on an AN/TPS-1D radar
at 286.5 degrees azimuth at 160 miles range. The blip was 2 to 3
times larger than any blip seen on radar set. The shape of the target
was that of a normal aircraft target as seen on a PPI scope. The
speed of the target was estimated at 6240 nmph. The target closed to
a range of about 45-50 nm, reversed direction and went outbound on
same azimuth without turning around or changing speed until
disappearing at a range of 160 nm (at the rim of the PPI
scope).  After a few seconds the "blip" reappeared and followed path
as mentioned above. This happened again for a third time and then the
blip disappeared from view. The total length of the observation was 5-6 minutes.
This seems like classic radar interference -- high-speed target on a constant azimuth inbound and/or outbound never crossing to the other side of the scope -- enabled by anomalous propagation conditions that helped bounce an interfering radar beam over longer distances.  There seems to have been a temperature inversion at around 7,000-8,000 ft (looking at the temps;  the AF didn't specifically mention that). 
Normally, without the temp inversion, the radar beams would not reach each other and there would be no interference.  However, the AF radar report noted they got lots of interference, which they called "rabbits."  On an old wartime TPS-1D they normally picked up most aircraft targets within 50 miles if I recall correctly, even though the range technically could go out as far as 160 NM (184 stat miles). 
Well, normal blips due to the width of the rotating beam, horizontally about 4 degs, are going look wide on the PPI scope, and blips at 160 NM are going look 3x the size of the same blip at around 53 NM.  That's normal.  At 53 NM the blip will appear to be about 3 miles wide!  At 160 NM the same blip will appear to be about 15 miles wide!  There are no objects that size causing a 3-mile or 15-mile blip, it's just the 3-mile width of the radar beam widening out to 15 miles wide.

One thing I can't explain is why the blips coming and going out on the same direction did not come closer than 45-50 NM.  If radar interference they should go all the way in to the center.  Maybe Martin Shough can help out here.