Combined L Band Avionics Systems
Combined L Band Avionics Systems
(OP)
Curiosity Question,
Has anybody seen any TCAS/ATC/DME retrofit products out there that use single multi-tasking L-band Receiver/Transmitters and antennas?
I thought I heard this pitched before, but can't see that anyone's actually building them.
Thanks
Has anybody seen any TCAS/ATC/DME retrofit products out there that use single multi-tasking L-band Receiver/Transmitters and antennas?
I thought I heard this pitched before, but can't see that anyone's actually building them.
Thanks





RE: Combined L Band Avionics Systems
Imagine a blade antenna 18" long, weighs 5 pounds, and has about 4 BNC connectors. The 2" wide base is screwed on with #8 screws directly to the 0.020" skin (in typical repair station fashion) of your favourite little Cessna. Sorry, this is a TCAS: TWO blades 18" long...
And in the process of eliminating the other three antennas, the guys blanked those off and drilled a new set of holes, because this one doesn't match any of the other three's hole patterns...
...or worse, they MADE it match...
I've seen enough hack jobs due to owners wanting the "latest" on their airplanes, that I really don't want to see one of those.
Steven Fahey, CET
RE: Combined L Band Avionics Systems
I sat in on an A380 briefing and seem to recall it has Honeywell combined TCAS/ATC antennas with a single LRU handling processing for radar, ATC and TCAS.
Most of the L band blade antennas I see ATC, TCAS Omni Directional and DME are 2" high.
The 18" antennas on a large jet are usually VHF and they do give the structures guys fits. I guess it's like a large tuning fork vibrating when there's significant cross wind.
RE: Combined L Band Avionics Systems
The above is why the DME antenna and the ATC antenna can look identical and often are in construction and characteristics. They often ARE identical.
However, although the suppression pulse "shuts down" the appropriate receiver at the proper time, that "shutting down" occurs electronically inside the receiver. Electronic isolation is not quite as effective as physical separation of the transmit energy from the receiver front end. And electronic isolation of lower energy levels is more effective than isolation of higher energy levels.
To protect the receiver front end from the very large transmit energy present in the multi-purpose antenna would require significant (meaning expensive) re-designs of both the DME receivers and the ATC receivers. Or such an isolation requirement would have to be built into the multi-purpose antenna itself, probably requiring the antenna to contain active components versus the current passive antenna design. Requiring active components adds circuits and installation wiring to provide power and control signals to the active components, plus active components typically cause a decrease in reliability over passive components alone.
With the current scheme of physical separation between the DME and ATC antennas keeping the energy levels of the transmissions that find their way to the receiver front ends at a much lower level, the suppression pulse just activates internal circuitry that can effectively block these lower energy levels without having to have high energy isolation circuitry in the receiver front end.
I have no doubt from a laboratory standpoint it can be done, but from a business standpoint I am not aware of any industry groundswell of demand for such an antenna combination. Especially on large commercial aircraft, the real estate is available for excellent physical separation without adding complexity.
I am not saying such an animal does not exist or will not exist, only that the above are some of the design considerations that would have to be addressed by some means to be able to market such a multi-purpose antenna.
debodine
RE: Combined L Band Avionics Systems
Thanks for the informed post.
RE: Combined L Band Avionics Systems
There is no difficulty in combining VHF/UHF/L-band or L-band/UHF/C-band but you'll need the help of the equipment OEMs before sharing one L-band antenna between systems.