#### shashank.ece

Joined Sep 11, 2008
2
i hav a question regardind radar system ..wat will happen when the target freq matches wit tat of clutter freq..hw is radar going to detect the target..its a dopplar radar..plz help

#### hgmjr

Joined Jan 28, 2005
9,029
Here is the wikipedia entry on doppler radar. It should give a little more background on the topic.

hgmjr

#### SgtWookie

Joined Jul 17, 2007
22,201
I have a question regarding radar systems ... what will happen when the target frequency matches with that of clutter frequency ... how is the radar going to detect the target ... it's a doppler radar ... please help.
In Doppler radar systems that were developed in the 60's and used in the 70's, ground clutter was "notched out" (supressed), as the clutter would otherwise "swamp" (reduce the sensitivity of) the receiver. When the Vc (closing velocity) of a target matched that of the clutter velocity, it was eliminated (removed) along with the ground clutter.

Newer Doppler radar systems have the capabilities via advanced signal processing techniques to extract a good deal of information from ground clutter.

However, that is not a discussion for this Forum.

#### beenthere

Joined Apr 20, 2004
15,808
I think the question makes a bit more sense if you substitute 'velocity' for 'frequency'. Clutter doesn't usually radiate.

#### SgtWookie

Joined Jul 17, 2007
22,201
I think the question makes a bit more sense if you substitute 'velocity' for 'frequency'. Clutter doesn't usually radiate.
Well, everything's relative.

No, "ground clutter" doesn't radiate, but it's problematic due to the relatively tremendous size of return from the transmitter, compared to other targets that are mobile. The greater the difference in velocity (or speed) between ground clutter and the target (within reason), the easier it is to pick out the target.

The "old school" way to do this was to pass the returned signal across multiple crystals that were encased in ovens, which made them stable. Each crystal was tuned to a slightly different frequency, and represented Vc from about -800 to around 1500 knots. This was a very expensive way to accomplish what is now done via digital signal processing. However, if ground clutter weren't notched out, the crystals would've really gotten hammered, and would likely have failed in flight.

#### beenthere

Joined Apr 20, 2004
15,808
Amazing they got it to work at all. So is picking out skin paints on a MiG down in the weeds with a 48 radar. Unless, of course, you have a little box that gets them to radiate IFF. Makes 'em real easy to spot (or did 30 years ago).

#### SgtWookie

Joined Jul 17, 2007
22,201
Amazing they got it to work at all.
Yes, it is.
So is picking out skin paints on a MiG down in the weeds with a 48 radar.
Mine was a 59. One of my former XO's was 1/2 of the only all-Marine team to shoot down a MiG 21 over 'Nam.
Unless, of course, you have a little box that gets them to radiate IFF. Makes 'em real easy to spot (or did 30 years ago).
I never heard that story, which I find somewhat odd; all of the senior NCOs and O's over O-2 had time in 'Nam.

I do know that many aircrew had aviation electricans install cig lighter sockets so they could plug in civvie radar detectors to give advance SAM warnings. Those civvie radar detector companies were actually approached by the military to build mil-spec versions. After wading through the specs, they basically told the heavies to jam it It would've cost 10k$each to produce mil-spec versions of detectors that they were selling for$100 retail.

We are so off topic that it's not even funny - but I don't really care.

Last edited:

#### shashank.ece

Joined Sep 11, 2008
2
thanks 4 ur help..nd ya by mistake i wrote freq ..u r rite its velocity

#### beenthere

Joined Apr 20, 2004
15,808
Well, forgive us for an old times moment. A good answer to your question is going to be too big to fit in this forum, and SgtWookie and I are no longer current with modern techniques of clutter suppression in doppler radars.

Wook - the gear was the QRC-248. We called it "Secret Squirrel". It interrogated MiG IFF's. Just got a book "Clashes" that is about the air war in 'Nam. It mentions the gear, so I don't think it's secret anymore. If you get the book, we're the cruiser (USS Jouett) with call sign Red Crown on page 262. We ended up with credit on a MiG 25.