On Aug 6, 1:52 pm, "William R. Frensley"
wrote:
Danny Deger wrote:
I would like thank everybody for all of the information. I have made
changes to my book to reflect Centers in general have skin paint
capability. There must be something unique about Washington Center's
radar out over the Atlantic Ocean Warning Areas that prevented them from
getting a skin paint on my friend's F-4.

There is one other aspect of primary radar that does not seem to have
been discussed: Most, if not all, airspace surveillance radars use a
"Moving Target Indicator" system to filter out the returns from fixed
terrain and structures. In essence this is a very narrow notch filter
centered at the radar's transmit frequency. Only returns that are
doppler-shifted a detectable amount from the transmit frequency are
painted on the display. This makes it difficult to detect turbojet
aircraft that are moving tangentially to the radar site. Rotating
propellers, on the other hand, usually produce a nice
frequency-broadened return and are usually easy to detect.

- Bill Frensley

Excellent point...I was trying desperatly to stay out of MTI!...

Most of the MTI's I am aware of occur in the baseband data
processing...but I suspect that the APRS 4 has a notch filter...or
did.

Robert