Thank you for supplying some interesting alternatives. Hadn’t thought of the 335 and a big saving on the 345.
The GNX 375 would mean a third GPS or replacing the 430 with a COM. I realise WAAS EGNOS gives you LPV, but for SEP light IFR LNAV is ok for me.
That’s a different thing; what you are doing is a bit like me watching Flightaware on a 4G-connected mobile phone while flying 
Back to the original Q: there is the B field but who could be using it? I can’t think of any case. ATC disregards the equipment list in most cases
Where does UK/EU airspace require you specify SBAS?
Nowhere AFAIK.
Quote
They display uncertified emitters too so no need for an SBAS GPS to feed the TXP. But no azimuth info.
Don’t want to take this thread off topic to the usual stuff
Sorry, thats wrong. Skydemon is showing my Pilotaware feed which accurately and clearly displays the location of PAW, Skyecho and ADSB aircraft.
Only some the remaining are without azimuth, but that is sorted if in range of a ground station.
I didn’t think I was going off topic, as I exactly upgraded a 330 to 330ES with Waas connection.
I thought doing that also to get my GTX 330 ESd. Decided to go for a GNX375. It’s the best value for money I think from Garmin. I am dumping the old mode S transponder with its previous century gray encoder. The GEA12 is a plug in on the back. I hope to be able to use the FIS B in conjunction with the ADL190. The WAAS & ADS-B is nice to have..when flying N reg it becomes implicit…the day you decide to sell it in the US.
Adsb is seen by all of the UK GA carry-on/Temp installed devices. Pilot aware and Sky echo.
They display uncertified emitters too so no need for an SBAS GPS to feed the TXP. But no azimuth info.
Don’t want to take this thread off topic to the usual stuff
@RobertL18C if as you say you’re interested primarily in ADS-B OUT to meet the US requirement in the limited airspace areas where it applies, a GTX 335 (versus 345) is designed for that purpose and can be purchased for installation by any mechanic, unlike the more costly 345 which has ADS-B IN too but by Garmin policy is sold and installed only by their dealers, who are also expensive. At least this was the situation in 2019 when I went through a similar review of options and settled on the 335. The result was much lower installed cost to meet the US airspace requirement, with some other benefits as follows.
My choice in the 335 was also driven by an interest in having as much of the equipment in the plane not permanently installed as possible and thereby easily upgradeable when the technology changes, as it always does. I also wanted to avoid Garmin Bluetooth in favor of reliable Wi-Fi for transmitting ADS-B information in the cockpit to multiple Foreflight equipped tablets and phone. With those factors in mind I use a Stratus 2S for ADS-B IN instead. Despite being easily removable, with some care it ended up as a clean installation that all starts itself with the master switch. I do appreciate having traffic info very much.
The Tail Beacon would work fine for your purposes too, and is super easy to install. But in my case the old King transponder and its encoder were on their last legs so it was efficient to replace them both with a 335 having internal GPS and integrated GAE 12 encoder options. I did have to install a Garmin GPS antenna but with remote encoder removed, no external GPS and no installed ADS-B OUT I have as little officially installed complexity in the plane as is possible, just one box and one antenna doing only what’s legally required for what will probably be a very long time. Along those lines the GTX with its antenna can also serve as a WAAS position input for some other avionics if needed, so one may not end up with multiple antennas all over the plane.
Adsb is seen by all of the UK GA carry-on/Temp installed devices. Pilot aware and Sky echo.
It’s for thos reason I upgraded my 330 to a 330ES.
I still do a lot of VFR and I want to be seen by anyone try to ‘see me’
There are still a lot that don’t bother but it’s getting better.
It deffo does – I see them all day. TCAS-1 is just that. It pings nearby Mode C/S boxes.
It’s not about Mode S data but about the type of transponder. I believe basic Mode C transponder won’t respond to TCAS interrogation.
Airliners use your Mode C (they disregard your Mode S) for a TCAS warning (TCAS-1).
For airliner-airliner RA (resolution advisory, TCAS-2) they use some Mode S based signalling whereby the two transponders (the two TCAS-2 systems) negotiate between themselves which one will tell his pilot to climb and the other one will tell his pilot to descend.
No light GA implements TCAS-2 so the only relevant system to carry (for avoiding a crash with a big jet) is good old Mode C. Mode S just enables the UK CAA to bust you much more easily, by broadcasting your tail # 
Nothing airborne can see any of your Mode S data. Exception: Avidyne TAS605 connected to an old Avidyne PFD via RS232 (not ARINC429) and then the PFD displays tail numbers, N-reg only. @Cobalt will remember.
I may have the above wrong but I’ve spoken to an awful lot of people about it and I am sure if it is wrong, wigglyamp will be here within the hour
