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Can a WAAS/EGNOS GPS tell if a non-WAAS/EGNOS antenna is used?

Can any WAAS GPS detect if a non WAAS antenna is being used?

I can’t see how it can, and I can’t see how it can make any difference (other than legal). This post is directly relevant to that argument.

Shoreham EGKA, United Kingdom

Yes, it can and it does.

Last Edited by dejwu at 09 Jan 12:20

You know what Q I will now ask

Shoreham EGKA, United Kingdom

A WAAS GPS hooked to a non-WAAS antenna is unable to receive HPL/VPL WAAS correction information from satellites and the GPS defaults to RAIM non-WAAS operation. So I learned in engineering class, correct me if I am wrong.
A good start to read is: .

Last Edited by dejwu at 09 Jan 12:55

I recommend reading the link I posted

Shoreham EGKA, United Kingdom

I had a look at it, but am too tired to sort that mess ;-).

It is my understanding that the differences between a WAAS TSO C190 antenna and a TSO C129 are primarily related to the antenna performance
requirements which include minimum and maximum antenna gain, frequency stability, power requirements, noise figure, mask angle, coupling and ground plane requirements, and mounting provisions. The WAAS antenna has greater gain and a lower mask angle. They both receive the same frequency and pass the preamp data on to the receiver for processing. It has been my experience that the TSO C129 antenna will function with a WAAS GPS system, but it may not meet the performance requirements for WAAS approaches.


What I wonder is how one could tell, since the difference between a WAAS and non WAAS antenna spec is less than the variations elsewhere in the installation.

Shoreham EGKA, United Kingdom

Here is the wording from our installation manual. It is a case of having to use an approved WAAS antenna if you want the Gamma 3 approval for LPV. You can use other antennas but you will not have an approved installation via our STC. Our IFD systems do not detect the antenna type. they merely use the signal and if it does not give the right signal then we will get integrity problems or not even pick up a sat signal at all. The GA56 is an example, it is not compatible with our systems. Nor is it compliant for approval.

The IFD5XX/4XX can be interfaced to all TSO-C190 antennas and the approved antennas listed in the table below. If connected to an approved WAAS Antenna, the IFD5XX/4XX is approved for TSO-C146d Gamma 3 operation.
The IFD5XX can be interfaced to non-WAAS antennas but the system will not be approved for any type of WAAS operations. In this case, the Antenna Type selection as described in Section 7.5.11 of the installation manual must be selected as “Non-WAAS”. This will result in the FMS functionality of the IFD5XX/4XX inhibiting selection of any WAAS (SBAS) approach in the database.

Approved GPS Antennas

Model Number Description Supplier
CI-428-200 GPS WAAS Antenna Cobham (Comant)
CI-2580-200 VHF/GPS WAAS Antenna Cobham (Comant)
CI-2728-410 VHF/GPS/XM Antenna Cobham (Comant)
GA-35 GPS/WAAS Antenna Garmin
GA-36 GPS/WAAS Antenna Garmin
GA-37 GPS/WAAS Antenna Garmin
GA-56A GPS/WAAS Antenna Garmin
GA-56W GPS/WAAS Antenna Garmin
GA-57 WAAS/XM Antenna Garmin
A33 (AT575-9UW) GPS/WAAS Antenna Garmin /AeroAntenna
A34 GPS/WAAS Antenna Garmin /AeroAntenna
AV-801 GPS/WAAS Antenna RAMI
AT575-93AVW-TNCF-000-RG-27-NM GPS/WAAS Antenna AeroAntenna Technology

Many thanks Steve for your input.

This requirement does remain a puzzle in the light of this analysis, which was posted by someone who is a real RF design specialist (he’s still “out there” but seems to have dropped off social media).

Our IFD systems do not detect the antenna type

They cannot, since the antenna is just a piece of analog circuitry, comprising of an L-band antenna and a pre-amp which is powered by 5V sent up the antenna cable from the GPS. There is no means of interrogating the antenna, like one does in “plug and play” PC products (e.g. the earliest CRT monitors with that feature had an I2C data channel via which the PC could interrogate it re its capabilities).

Presumably this one would not be W compatible

Shoreham EGKA, United Kingdom
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