On Sunday, May 6, 2018 at 8:42:20 AM UTC-7, Darryl Ramm wrote:
On Sunday, May 6, 2018 at 8:12:34 AM UTC-7, Craig Reinholt wrote:
On Sunday, May 6, 2018 at 6:25:25 AM UTC-7, wrote:
My message for a long time has been: If you fly near areas of dense airliners, fast jets and military traffic, just get a transponder, Mode S or used Mode C does not matter... get what you can afford.


This seems logical, but I heard another corner case where might not be so.

I sat in a presentation from our local Approach Control folks. They noted that with the new ADSB ground stations they had better visibility than from their existing radar plus ModeC. Specifically, low and far out. This like it might permit them to route controlled traffic in new places where gliders are, but where a Mode C transponder on the glider might not help.

Unfortunately, what the Approach Control folks failed to mention that their software removes targets of anything less than 70 mph ground speed. This is to remove the clutter from highway traffic. It also removes most gliders unless we have electronic identification measures. YMMV with each approach personnel. PDX was pretty clueless about gliders and their senior controller didn't know what the 1202 transponder frequency identified. They have since programed 1202 to print "glider" on their screen.
Craig

And to be very clear on what Craig is saying, he is talking about primary radar doppler discriminators filtering slow moving aircraft so they are not seen on ATC primary radar, this is *not* SSR (Secondary Surveillance Radar) that detects transponders. If your glider has a transponder it will be seen by ATC via SSR any time it is within SSR coverage, independent of airspeed.

I have to say this because I know there is still confusion out there, including hearing people get this completely backwards and claim that this filtering is an issue with transponders, it's not... its a reason why you want a transponder.

Aaak! Sorry for not being clear on my post. What Darryl said!