I have scheduled a full respray of my aircraft and I thought it will be a good idea to also replace my existing 3 GPS antennas in preparation for a future WAAS upgrade of my old GNS530 or a possible replace with something from the GTN series.
The existing Garmin antennas are the old tearshaped model. The new, WAAS compatible models from Garmin I can find are the GA 35, 36 and 37. Does anyone know what would be the best model to choose in order to be sure it will be compatible with existing and newer avionics?
At a first glance they all seem to do the same job. Any help would be appreciated.
Thank you!
A couple of avionics people are @garryiae and @wigglyamp – not sure if they are still contributing though. On past record, an avionics installer who contributes well gets a lot of business from EuroGA 
A WAAS antenna is practically identical in performance (if not in price, or legality) to a non-WAAS version. The “classic” post which demolishes the “WAAS antenna is much superior” argument is here. @tomjnx is still “out there” but busy on other stuff; I was in contact with him recently about something to do with antenna design.
The GA35 antenna is the WAAS replacement with the same footprint as the legacy GA56 used with non-WAAS GNS units.
Keep in mind that you will also need to crimp a different connector onto the antenna cable: GA56 has a BNC connector, GA35 has a TNC one. In principle, one can just use a BNC-to-TNC adapter, it won’t absorb more than 0.3 dB, but I am not sure it is officially approved – if anyone has a regulatory reference, please post it here!
Also make sure you have the correct coax cable. When you upgrade a non-WAAS unit to WAAS, the GA35 is part of the package. So make sure you do not pay twice.
Aviathor wrote:
Also make sure you have the correct coax cable.
Just to add, I would recommend replacing the connector for a TNC rather than using an adapter, adding more attenuation on a WAAS system is not a good idea and generally the cables are accessible enough to change the connector.
You also need to consider how the new Antenna’s are going to be certified, Garmin have an STC but that calls for a specific doubler plate to be manufactured and used, another alternative is CS-STAN and confirming conformity with the applicable Antenna Chapter.
Any queries or if you need pricing on upgrading or replacing with a GTN please feel free to contact me
Thank you for your replies! I will use the TNC connector and the new cable.
So there is no need to purchase GA36 or GA37, as they don’t have better SN ratios or extended capabilities?
AlexTB20 wrote:
So there is no need to purchase GA36 or GA37, as they don’t have better SN ratios or extended capabilities?
No, GA56 and GA35 are teardrop-shaped, whereas GA36 and GA37 have an ARINC 743 oval footprint. GA37 also provides XM weather reception, which you don’t need in Europe anyway.
