GPS Output Query

[ian_th]

Follow on query from the Power cable query.

With the approval of CS-STAN Amendment 3, we are now going to take advantage of it and connect the GPS from the PAW to a Trig TT31 transponder. Straight forward as the procedure is well documented.

We have a Garmin 225 radio which has a GPS input. It would be a shame not to take advantage of this so that the radio provides confirmation of the station of the frequency selected and a few other options.

As the PAW is a "temporary" install, it has to be easy to remove and therefore the connections would be via plugs & sockets.

Has anyone have experience of splitting the GPS output from the USB-RS232 module and if so how?

Thanks
Ian

 

[JCurtis]

Check the CS-STAN as I thought the connection required the sender be approved by the transponder manufacturer. I also seem to recall it has to be a direct connection, so no splitting a single source to multiple destinations.

The final issue of the latest CS-STAN is different to the last issued draft.

[JCurtis]

The transponder manufacturer must state that GNSS receiver, PAW in this case, and the transponder are compatible.

For configuration 3:
The following conditions apply to configuration 3:
— The transponder equipment and its installation are compliant with CS-SC002c or later amendments, or are otherwise approved.
— The ADS-B transmit unit (transponder) is approved in accordance with ETSO-C166b, or later revisions, or the equivalent.
— The GNSS receiver is not approved or its installation is not certified. However, the compatibility of the combination of the transponder and the GNSS receiver is explicitly stated by the manufacturer of the transponder.
— The quality indicators are configured according to the manufacturer instructions to report the lowest quality (e.g. SIL = 0 and SDA = 0, NACp = 0).
— The installation instructions from the equipment manufacturer have to be followed..

The direct connection bit is for configuration 1, so that can be ignored.

There is a direct digital interface between the GNSS receiver and the transponder, or the GNSS receiver is integrated into the transponder.

[ian_th]

Thanks for the info, I missed the para re the comparability.

I will email Trig support over the weekend.
I don't think that there will be a problem as there is a question in their FAQ section for ADS-B regarding using a FLARM GPS as a position source.
PAW outputs the NMEA protocol which is compatible with Trig transponders.

The direct connection bit has been ignored.

[grahambaker]

As it’s an EASA aircraft it may be worth checking with your avionics engineer that connecting an uncertified source to your radio is permissible. Seems trivial, but it would be annoying if you went to the trouble of doing it, to find it disconnected for you at the next annual.

[ian_th]

Update on the 2 comments.

Compatibility
Support at Trig Avionics have replied with a reference to the TT31 Installation Manual section 2.7.12 GPS Input. This lists the protocols that are recognised one of which is output from the PAW.
In addition they are going to add it to their FAQs online.

Connection to a Radio
I have discussed this with the avionics engineer who will be carrying out the work and it is not an issue.
The work is being done through our service organisation so they will be aware of these changes.

Thanks for your comments. That is where these forums are helpful as other members think of things that you don't.

Ian