On Friday, February 17, 2017 at 8:19:58 AM UTC-8, wrote:
I believe it's worthwhile for an experimental glider to transmit adsb-out, even if only using an uncertified gps, because it will make your glider show up more accurately on Flarm receivers even if you don't carry flarm yourself (adsb-out targets show up on flarm with exact location and altitude). You should also show up for equipped power aircraft even if out of ATC radar contact.

The main reason to pay for a certified gps to send adsb-out would be if you also plan to install adsb-in and a traffic display. I still don't see a low-cost low-power adsb-in system for a glider, although I'm sure they will come. The FlightBox adsb-in device appears to draw 1.3A at 5V, ie probably 0.7A at 12V, which would be too much for my glider battery. Also, I would want a sunlight-readable display (I don't find iphones etc to be sunlight readable).

I don't plan to install flarm in my glider, because I think transponder+adsb will soon be the better choice.

Better choice? For what? You not planning to fly much with other gliders?

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One wrinkle to be aware of is certified ADS-B In systems will *not* see your traffic at all if it is using a non-certified/non-compliant ADS-B source. They are as anal-retentive as the FAA ADS-B ground infrastructure (or rather last year the FAA made the ground infrastructure deliberately as anal-retentive as the airborne certified ADS-B In systems to discourage use of non-compliant GPS sources partially to help force better compatibility with those certified airborne ADS-B In systems).

So folks who have an experimental glider sure they can hook up any old GPS source say to a Trig transponder, and it will show up on PowerFLARM and non-certified ADS-B In systems. But really not a good idea, probably not a good idea to talk about without being clear on the limitations, especially now there is a Trig TN72 GPS is suitable for use in experimental gliders and does not have those limitations (Lots of discussion on the TN72 on other threads on r.a.s.). But if folks have an experiential glider with a Trig transponder and want ADS-B Out the TN72 is really now likely the minimum they should be thinking of.