Wiring two GPSs into the system

[DougN]

I've got two GPSs - an IFR Garmin GPS-155XL (just added) and a portable AvMap EKP-IV (mounted into the panel - had it for a couple of years).

The IFR GPS is now the primary one, and it is wired as an ARINC source into the HS34 (as required). The Avmap is also wired into the HS34 as a second nav source using a serial input. The installation manual states that the GPS should also make its serial line available to the EFIS in addition to the Arinc to the HS34.

"...and/or EMS, your GPS must output either “aviation format” or the following NMEA sentences in its serial stream: $GPRMC, $GPRMB, $GPGGA, and one of $GPBOD$GPAPB. You must also have a supported cable that exposes your GPS’s serial transmit line..."

So, i run a line from the GPS 155XL's serial output to the EFIS's serial input.

Am i reading this correctly? And, will the Dynons get confused as to which GPS is primary? Must i slave the AvMap's fix to the Garmin's to prevent redundant, non-equivalent position info? Or will this work fine? (one of the ironies is that the AvMap is a WAAS GPS while the IFR Garmin one isn't)

What's your take on this setup?

Thanks,
Doug

 

[DougN]

As a followup. How many Nav sources will the HSI identify (i have an SL30)? I'm hoping 3: NAV1, GPS1, GPS2.

I'm also hoping for 4 bearing sources: NAV1, NAV Stdby, GPS1, GPS2.

Thanks again,
Doug

 

[PhantomPholly]

You should not need both ARINC and Serial streams from your primary to your Dynon. ARINC is superior, providing vertical guidance.

If you do as you suggest (connect both serial and ARINC from the same GPS), the HS34 will see these as two separate GPS data sources. In your example, it would "see" GPS1, GPS2, and GPS3 (including your other GPS).

This is not harmful, and in fact if you are a belt-and-suspenders type could allow you to keep using your primary GPS in the unlikely event that a wire jiggles itself to a poor ARINC connection during flight.

 

[dynonsupport]

If you hook the GPS to the EFIS serial port, it will only use this if the HS34 ever fails. You cannot use the EFIS/EMS serial ports when an HS34 is present, and data on them is ignored. You do not have to hook the GPS to the EFIS if you do not wish to. I believe the passage you are reading assumes you do not have an HS34. I would not hook the GPS to both ARINC and Serial on the HS34. This will "work" but it would also be confusing, since you would have a GPS1 and GPS2 source that are the same.

If you have an HS34, I would hook the 155 via ARINC and the Avmap via serial. You can identify one as GPS1 and the other as GPS2, and switch as you wish. It will also identify a variety of NAV bearing sources as you mentioned.

In your specific case, you must have an HS34, and you have to wire the 155 via ARINC. This is because the HS34 has two serial ports, and you'll use one for the Avmap and one for the SL30.
Additionally, We do not support two GPS units hooked up unless you have an HS34.