On Oct 9, 9:30*am, tomlusch
wrote:
;665691 Wrote:



On Oct 6, 10:31*pm, tomlusch
wrote:-
;663552 Wrote:

-
Continuing problems seeing ATCRBS transponders with Mode S
interrogators-
-
Hey all, I work in, lets call it 'an associated industry' and we are
still seeing ATCRBS transponders that reply to some interrogators,
and
not to others.-
-
At one time this was known as the 'P4 problem', sometimes as the
'Terra problem', just want to ask if anyone out there flying with an
ATCRBS xpdr is still having trouble being 'seen' by some
interrogators, but no problem with others.-
-
Thx--
-
Dave-

Funny that you should pose such a question Dave. *Just yesterday
evening I observed a primary target with our ASR-9 (Mode S) moving
ENE
at a decent clip. *Used a different display and selected our nearby
ARSR (an ATCBI-6) sensor, and saw a rock solid beacon reply, showing
that it was an aircraft at 13,000 ft msl. *Never did see a
transponder
return using our ASR-9. *

Take a look at my previous experience with this type of transponder
behavior...

http://home.columbus.rr.com/lusch/talotta.html

..and get in touch with me. *

Tom Luschhttp://tomlusch.com

--
tomlusch-

Hey, Tom. Yeah, I'm familiar with your reports on this / these issues,
back when I was building a simulation model of transponders.

Seems there are some really old transponders out there, or
'some' (heh) that just don't meet spec.

Dave

Dave,

Of course, those "really old" transponders met the _original_ TSO spec
before Mode S came on the scene. *I personally put in a lot of time and
effort back in '95 to get a King KT76 fixed, when there was no problem
with it (other than it was acting like a Terra TRT-250 at the time).

I've been noticing that it seems that more and more transponders
*appear* intermittent on our ASR-9 these days. *They'll show as a good
beacon target, then become a RDR (primary "skin paint") target, and
flip flop between these two states. *It is as if they have weak
signals. *I notice this on typical low-end aircraft (especially on 1200
squawks on nice VFR days). *I haven't observed this phenomenon on
higher-end aircraft. *

Yet, when I view these same intermittent beacon targets
*simultaneously* using our nearby ARSR, it shows rock solid beacon
replies. *It seems to have no problem seeing them. *There is a definite
difference. *

I recently came across the following statement...

"Turning off Mode-S: A Maintenance Alert was issued on 6/1/2006
instructing BI-6 sites to stop interrogating Mode-S." *

That note is still present at...

http://www.aos.jccbi.gov/atcbi-6/faqs.htm

*IF* the ARSR I'm watching with is using classical interrogations, and
our ASR-9 is in Intermode (Full Mode S), that *may* explain what I'm
seeing. *

Conversely, I wonder if possibly an *Interim* Mode Interlace Pattern
(MIP), which must've been implemented on our Mode S sensors to deal
with the "Terra problem," has been adjusted, and they aren't doing as
many "classical" (i.e. without P4) interrogations. *I have yet to
determine if we're in "Mixed Mode" or are *fully into "Intermode" (Full
Mode S) with our ASR-9.

Tomhttp://tomlusch.com

--
tomlusch

Interesting...

Was there any explanation for turning off Mode-S on those?

Dave