Transponder, ADS-B and 2020 compliant.

B

bluesideup

Line Up and Wait
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bluesideup
Hi everyone.

I am not sure how many of you have had a problem with the Xponder when you upgraded to the 2020. It looks like the interrogation rate required by the protocol kills many transponders, and not just the older models. It looks like some of the Dynon are also affected?

Any feedback?

Thank you.
 
There is no "interrogation" for ADS-B. It is a randomly timed broadcast on an approximately 1 update per second rate. What exactly are you asking about?
 
Clark1961 said:
There is no "interrogation" for ADS-B. It is a randomly timed broadcast on an approximately 1 update per second rate. What exactly are you asking about?
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I believe he's talking about Mode-S which can be interrogated very rapidly if, for example, a fully equipped TCAS aircraft is converging on a Mode-S plus extended squitter target. It'll ask repetitively and rapidly to get the information it needs for an RA in the TCAS equipped aircraft.

I haven't seen any links or anything solid (and the OP didn't provide any) to anything that would indicate anyone's Mode-S transponders are locking up when triggered rapidly, but I guess I could see it if they didn't test maximum response rate. A corner case, for sure.

But I haven't read about any ground-to-air ops that require "fast update" like that. Yet... I suppose. Maybe that ill-fated FedEx ADS-B test in MEM did something like that.
 
denverpilot said:
I believe he's talking about Mode-S which can be interrogated very rapidly if, for example, a fully equipped TCAS aircraft is converging on a Mode-S plus extended squitter target. It'll ask repetitively and rapidly to get the information it needs for an RA in the TCAS equipped aircraft.

I haven't seen any links or anything solid (and the OP didn't provide any) to anything that would indicate anyone's Mode-S transponders are locking up when triggered rapidly, but I guess I could see it if they didn't test maximum response rate. A corner case, for sure.

But I haven't read about any ground-to-air ops that require "fast update" like that. Yet... I suppose. Maybe that ill-fated FedEx ADS-B test in MEM did something like that.
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If he is typing about mode-s then it has nothing to do with the 2020 ADS-B mandate. He should slow down and be specific about his question.
 
Clark1961 said:
If he is typing about mode-s then it has nothing to do with the 2020 ADS-B mandate. He should slow down and be specific about his question.
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Probably. But so few people even have any idea how a transponder works... that everything wrong with a transponder today must be "because ADS-B!!!! ERMAGERD!"... LOL.

I'm already completely annoyed at having to explain that "ADS-B" isn't a protocol anyway... it's just a basket of deplorable technologies.

(Oooh, I got to use basket of deplorables! LOL! Okay, I know it's weak... I'm distracted here... picking up where the boss/co-worker left off with a Comcast negotiation now that he's out for a bit... uggggggnnnnnhhhh... not quite to the "want to pluck my own eyballs out of my face" stage yet, but think that's going to start after the next e-mail.)
 
denverpilot said:
Probably. But so few people even have any idea how a transponder works... that everything wrong with a transponder today must be "because ADS-B!!!! ERMAGERD!"... LOL.

I'm already completely annoyed at having to explain that "ADS-B" isn't a protocol anyway... it's just a basket of deplorable technologies.

(Oooh, I got to use basket of deplorables! LOL! Okay, I know it's weak... I'm distracted here... picking up where the boss/co-worker left off with a Comcast negotiation now that he's out for a bit... uggggggnnnnnhhhh... not quite to the "want to pluck my own eyballs out of my face" stage yet, but think that's going to start after the next e-mail.)
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If you need help with the eyeball plucking I know a guy...
 
denverpilot said:
You want a toe? I can get you a toe by 3 o'clock this afternoon!

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No. It's the eyes or nothing. Well maybe not nothing. Could also prolly do arm and leg perhaps with gonads thrown in for entertainment.
 
Clark1961 said:
No. It's the eyes or nothing. Well maybe not nothing. Could also prolly do arm and leg perhaps with gonads thrown in for entertainment.
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The gonads are all in use by the ADS-B marketing people who say it's all about "safety". They'll be available for lease again in 2020, would you like to make a reservation? :)
 
murphey said:
And I'll sell tickets.
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The one act Clark mentioned, their "cut" is too big on the till, and they take "an arm and a leg". ;)

The toe guy is pretty cheap though, considering. He kinda looks like Paul Bunyan or Doctor Scholl, they say.
 
bluesideup said:
Hi everyone.

I am not sure how many of you have had a problem with the Xponder when you upgraded to the 2020. It looks like the interrogation rate required by the protocol kills many transponders, and not just the older models. It looks like some of the Dynon are also affected?

Any feedback?

Thank you.
Click to expand...

If the transponder is designed to the DO (aka RTCA) and TSO specs, there should not be an issue. Mode A /C transponders are designed to limit their replies at 1200 PRF (Pulse Repetition Frequency) - at 1200 PRF the reply rate shall no more than 95%. As the replies increase, the reply rate of the transponder decreases thereby protecting the transponder from high duty cycles and reducing frequency congestion. Mode S transponders interleave the Mode A/C function within the Mode S function.

Mode S (with TCAS II) is designed for an aircraft density of 0.3 aircraft per sq nmi. The spec is: TCAS II shall provide resolution advisories in the vertical dimension (climb, descend) in airspace densities up to 0.3 aircraft per sq nmi. This equates to 24 aircraft within a 5 nmi radius of a TCAS II equipped aircraft.

On the airborn side; as stated above, Mode S / ADS-B broadcasts (squits) its information once a second. Also, TCAS sends an All Call, and then then interrogates the responding aircraft in its airspace once a second with TCAS interrogating both Mode A/C and Mode S aircraft. TCAS II also has the capability to actively track and display up to 31 aircraft with additional aircraft in "monitor" status. Each of the aircraft in track is interrogated once per sec by TCAS.

On the ground side, the ground stations will interrogate the Mode A/C transponder once every 5 seconds or 10 - 12 seconds depending on the airspace. In the terminal / approach environment the interval is up to 5 sec whereas in the en route environment it is 10 - 12 seconds. Also, if equipped, the ground stations will broadcast the TIS data on the 1030 MHz Mode S link.

A number of techniques a used in TCAS to decrease the amount of RF traffic. For example, TCAS can focus it's interrogations for a specific target in a specific direction. Also, with Change 7.1 TCAS includes Interference Limiting. As TCAS senses higher traffic density it will decrease its transmit power to decrease the range of the interrogations to those aircraft that pose the greatest threat and periodically monitors the other aircraft in the track list.

Hope this gives some sense to what occurs on the transponder frequencies.
 
Axtel4 said:
If the transponder is designed to the DO (aka RTCA) and TSO specs, there should not be an issue. Mode A /C transponders are designed to limit their replies at 1200 PRF (Pulse Repetition Frequency) - at 1200 PRF the reply rate shall no more than 95%. As the replies increase, the reply rate of the transponder decreases thereby protecting the transponder from high duty cycles and reducing frequency congestion. Mode S transponders interleave the Mode A/C function within the Mode S function.

Mode S (with TCAS II) is designed for an aircraft density of 0.3 aircraft per sq nmi. The spec is: TCAS II shall provide resolution advisories in the vertical dimension (climb, descend) in airspace densities up to 0.3 aircraft per sq nmi. This equates to 24 aircraft within a 5 nmi radius of a TCAS II equipped aircraft.

On the airborn side; as stated above, Mode S / ADS-B broadcasts (squits) its information once a second. Also, TCAS sends an All Call, and then then interrogates the responding aircraft in its airspace once a second with TCAS interrogating both Mode A/C and Mode S aircraft. TCAS II also has the capability to actively track and display up to 31 aircraft with additional aircraft in "monitor" status. Each of the aircraft in track is interrogated once per sec by TCAS.

On the ground side, the ground stations will interrogate the Mode A/C transponder once every 5 seconds or 10 - 12 seconds depending on the airspace. In the terminal / approach environment the interval is up to 5 sec whereas in the en route environment it is 10 - 12 seconds. Also, if equipped, the ground stations will broadcast the TIS data on the 1030 MHz Mode S link.

A number of techniques a used in TCAS to decrease the amount of RF traffic. For example, TCAS can focus it's interrogations for a specific target in a specific direction. Also, with Change 7.1 TCAS includes Interference Limiting. As TCAS senses higher traffic density it will decrease its transmit power to decrease the range of the interrogations to those aircraft that pose the greatest threat and periodically monitors the other aircraft in the track list.

Hope this gives some sense to what occurs on the transponder frequencies.
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I love it when someone talks engineering/dirty to us. ;)

Good info. How long is the "squit", time-wise?

Just reading those numbers makes it clear why Mode-S couldn't handle dense airspace properly as the only ADS-B solution and UAT was slapped in. Of course they also needed a carrot to interest anyone... the data uplink side of UAT.

And still some of us aren't completely interested, at the price points prior to about this year. 25% uptake on a tech that's been out for many years is pretty awful from a marketing and sales perspective.
 
denverpilot said:
Good info. How long is the "squit", time-wise?
Click to expand...

It depends on if it is a Mode S Short or Mode S Long transmission. The total duration for a Mode S Short transmission is 64 micro seconds (uS) while a Mode S Long is 120 uS. Mode S Short comprises of a 4 pulse (aka bit) preamble followed by a 56 bit pulse stream. Mode S Long comprises of a 4 pulse preamble followed by a 112 bit pulse stream. The preamble is 8 uS and the pulse stream is either 56 uS or 112 uS. The width of each pulse is 500 nano seconds spaced at 1 uS intervals.
 
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