“I believe you need a GTX330ES model to get Mode S out. That’s what the ES gives you. At one point converting a straight GTX330 to GTX330ES was a $2000 upgrade”
This isn’t correct. A standard GTX330 broadcasts Mode S data (including Enhanced Surveillance parameters where configured). The ‘ES’ just adds ADS-B OUT parameters.
The upgrade currently costs about $1500.
Thanks for the clarification.
Peter wrote:
You can actually get Mode S data to come out of the (any version) GTX330, and you can do automated GND/AIR mode switching based on GPS ground speed, but you don’t need that.
Is GPS GS sufficient? (In EASA-land.) The IM for the Trig TT31 mode S transponder says that you need both GPS GS and an ADC. I don’t see why Trig would have done it that way unless it was a regulatory requirement.
You don’t need any GPS data for a legal Mode S installation.
I have no GPS connection to my 2005-firmware GTX330.
Well, I have the KLN94 ground speed connection but that never worked, despite me paying 500 quid for it. Garmin recently did a firmware update which ever so cryptically mentions “KLN89” and I think that they may have fixed that, 10 years + later. It was always in the GTX330 IM but clearly did not work.
100% legal Mode S and been all over Europe in it.
You need just a GTX330, its antenna, a power wire (via a CB) and a pressure altitude source.
The stuff about radiating GPS position, speed, autopilot preselect, whatever else, that is Enhanced Mode S, which is (was?) mandatory over 5700kt / 250kt TAS / 18 seats and was actually prohibited below that (an embarrassing reg which was never enforced, once Europe realised that most avionics are made in the US where Elementary/Enhanced never existed, but one well known avionics installer wrote in a UK magazine that he was required to strip out the GPS connection in loads of planes) 
The 5700kg+ stuff is where certified ADS-B OUT is required today, but not where the OP is, where a giraffe eating your antennae is a more pressing problem
“…. but not where the OP is, where a giraffe eating your antennae is a more pressing problem…”
which is why the t’ponder antenna is on the lower fuselage, where giraffe struggle.
Thanks, guys – slowly absorbing the posts above.
We got our Mode S allocation from the KCAA in binary today, so anyone struggling with converting to hex might find these links useful:
http://www.kloth.net/radio/icao24lookup.php
and
Peter wrote:
You don’t need any GPS data for a legal Mode S installation.
Of course not. I was talking about the automatic GND/AIR switching.
We’ve had a GTN650 and GTX330 interconnected combination for years. It’s great because you only ever needed to press buttons when changing squawk code and could do that on either box (and it displayed the new code on both). After powering up on the avionics bus, it would remain in GND mode until airborne (based on groundspeed passing something like 30 or 40 knots) when autoswitched to ALT, then reverted back after landing. I’d agree it’s slightly easier punching in the new squawk codes on the GTX box directly, especially when reverting to VFR 7000, but easier to view/check the code is correct on the GTN because it’s closer to field of vision.
We upgraded to GTX330ES earlier this year which automatically “squits” the GPS location regardless of receiving radar pings. The box looks and operates almost identically (you can tell really only by the startup screen display) but instead it always displays ALT mode, never GND. Apparently something to do with the ADS-B out.
I am a little nervous about drifting from the subject
but just to confirm, the experience of DavidC is the same as mine re the ES upgrade
