N

NM Doug

Well Known Member
I know the Navworx TransMonSPE is intended to pick up the encoded altitude and squawk by sniffing the info from the transponder cable (for older transponders that can't talk to the Navworx box otherwise).

Does the transponder have to be interrogated by a ground-based radar for the Navworx to send an ASD-B OUT signal via its UAT antenna, or does the Navworx box send periodic OUT messages, even if the transponder hasn't been pinged for awhile?

(The question came up because if one of the Nextgen objectives is to reduce reliance on ground-based radar, it's likely that there may be fewer ground-based radars eventually and maybe less frequent pings, especially in more remote areas.)
 
I believe this is one of the short-comings of this particular system. In fact I am surprised the FAA allows this. For example, at LVK we are in a valley, and there is no radar coverage for aircraft in the pattern. But we are inside the SFO mode C veil, so by 2020 all aircraft in that pattern are supposed to have a working ADSB-out box. I do not know what will happen when the FAA finally figures this out.
 
I'm not an expert at this system, but it does sound like there is a bit of a hole there - maybe someone from NavWorx can explain.

As far as I know, the NavWorx box will broadcast ADS-B Out messages periodically, regardless if there is a ground radar station around or not. This means it will broadcast squawk, pressure altitude, gps altitude, and position independent of any ground station.

However, if you haven't been pinged by radar lately, I'm not sure how it will update pressure altitude?

One thing I'm not sure about is the squawk code, does ADS-B Out even use the squawk code (since it has the ICAO code instead)? Maybe it's just looking for code 1200 to go into 'anonymous mode'.
 
I have a Navworkx ADS600-EXP and a TransmonSPE clamped on my KT76A antenna cable.

The ADS600 transmits data every second whether the transponder is being interrogated or not.

When not being interrogated, it transmits ICAO code ( also known as Mode S code), GPS position, GPS Altitude, Speed.

When being interrogated, it adds Squawk code and Pressure Altitude.

The ADS-B system is designed to work without radar
 
ok, so other than not seeing 1080-only traffic when out of contact with ground stations (to be corrected with future firmware update), none of the shortcomings or holes that were alluded to in previous posts exist, correct?

thanks

erich
 
49clipper

speaking of being pinged. My Kt76A recently quite blinking the interrogation light on a trip and i was within 30 miles of two major airports with approach radars. No pings at all. My avionics tech told me in can be interrogated and not blink. It has to do with the older technology in the -76A and the incandescnet bulb. He says try it again and ask them if they see me. True? Getting back to STL and it started blinking again.
 
erich weaver said:
ok, so other than not seeing 1080-only traffic when out of contact with ground stations (to be corrected with future firmware update), none of the shortcomings or holes that were alluded to in previous posts exist, correct?

thanks

erich
Click to expand...

I thought sending pressure altitude was a requirement for 2020 compliant ADSB-out. If it's not, why bother with the TransMon? If it is, then sometimes it's not in compliance. Is there a third possibility?
 
BobTurner said:
I thought sending pressure altitude was a requirement for 2020 compliant ADSB-out. If it's not, why bother with the TransMon? If it is, then sometimes it's not in compliance. Is there a third possibility?
Click to expand...

It was my understanding that whole justification for ADSB, long-term, was to get rid of radar, primary and secondary, while improving location accuracy. It was my understanding that the primary source of position and altitude is GPS. I understand the use of radar, short term, is for both redundancy and system transition.

In my opinion the important thing they want from the transponder is not altitude, it's the sqwuak code.

I assume that the ADSB unit always has GPS altitude and sends it but the FAA wants the pressure altitude for redundancy and legacy system compliance (remember, just because they made you upgrade, doesn't mean they're going to upgrade all of their systems). I believe that Squawk codes are here for a while, as a LOT of ATC systems and software would have to be replaced to use unique aircraft identifiers. Further, they need squawk codes until they have replaced all radar-based systems with ADSB and forced 100% ADSB compliance in aircraft, as that is the only way those systems can identify aircraft. The ATC system is, will be, a patch work of radar and ADSB networks that must talk to one another using common language (least common denominator). The guy at O'Hare approach will see all the ADSB data goodies on his screen, but he needs to hand you off to Rockford approach or Chicago Center over Iowa and they will be on Radar-based systems and will continue to be until the FAA forces everyone flying over Iowa to have ADSB and they upgrade those systems. ATC can only provide separation if they can see you. Radar let's them see you without your participation, ADSB requires participation for them to see you. The 2020 push is just for the busy terminal airspace.

I was just thinking, does the FAA even require that you send pressure altitude in the ADS-B message? They'll get it directly from your transponder via their legacy systems.

Larry

Larry
 
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