Digital encoder for ADS-B out ?

[Mooneys R Quicker]

I have a question for the tech savey . I'm considering and shopping for an ADS-B out transponder and was wondering if when pricing all the units do I need to consider an encoder also? I was thinking with the waas gps that one would not need the encoder. After all if they can tell "exactly" where you are within a few feet why the encoder? If one is needed, would anyone have a good suggestion? Thanks in advance for your time.

 

[Capt. Geoffrey Thorpe]

The ADS-B altitude data has to come from the same encoder as yea olde transponder. It does not come from your GPS, WASS or not.

The need to replace your (I assume existing) encoder would depend on your choice of ADS-B out and (existing) transponder hardware and how they communicate.

Some ADS-B units "listen" to your transponder signal to get the code and altitude, some directly attach to the transponder.

 

[vontresc]

You still need an encoder in most cases. The units will still be able to listen to your old grey code encoder. Garmin has a $200 encoder you can plug into the back of the GTX-3X5, and some like the Trig TT-22 have built in encoders. Generally the "standard" size GA ADS-B transponders still need an external encoder, since you are still broadcasting a mode C/S signal.

 

[bnt83]

They all need pressure altitude, very few of the new ADS-B out transponders have an internal pressure altitude encoder. Even if it has an interal GPS it still needs a pressure altitude reference.

I'd say you are more likely able to re-use the exsiting transponder encoder but may opt to install a brand new one anyway since they aren't terribly expensive and seems like reasonably cheap insurance. The one I put it was a more expensive one around $325 IIRC. Also put in a brand new antenna since I don't want a 35 year old antenna screwing up my new $4500 transponder.