Toggling CDI changes DME

[russgreen 1]

Toggling the CDI between GPS and VLOC seems to change the sim/cockpit/radios/nav1_dme_dist_m dataref making seperate DME radios display distance to next GPS waypoint and not the tuned station on GTN Nav frequency.  This seems to be very odd behavior.

[RXP 2,336]

Hi,

The GTN overrides the NAV dme datarefs when in GPS mode, and you enable "Connect GPS to VOR".

Since v2.5.25, in addition to the 'dist' dataref, it also overrides the 'time' and 'speed' DME datarefs.

It didn't before because the datarefs documentation was wrong and a recent discussion with XPlane devs cleared this up!

Edited May 18, 2020 by RXP

[russgreen 1]

Why would the DME (say a Bendix King KN62 type unit) suddenly report distance to a GPS waypoint?

Edited May 18, 2020 by russgreen

[RXP 2,336]

I don't know, but if you're enabling "Connect GPS to VOR1", the GTN is then replacing the radio signals from NAV1 with synthesized signals so that the panel instrument is displaying valid data still.

Do you need "Connect GPS to VOR1" for this aircraft? Do you have any mean to use DME2 from NAV2 instead?

This is a good suggestion though and XP11 permitting, we might add a specific "DME" option in a future update.

[russgreen 1]

Well possibly. Depending on the aicraft.  

Take the default 172.  If you're using the GTN as NAV/COM1 you'd want to connect to VOR1 wouldn't you?   

And if you had a DME radio on the panel set to remote to nav 1 it would continue to use the NAV station tuned on the GTN but if you override all the DME datarefs that breaks.

Edited May 18, 2020 by russgreen

[RXP 2,336]

46 minutes ago, russgreen said:

And if you had a DME radio on the panel set to remote to nav 1 it would continue to use the NAV station tuned on the GTN but if you override all the DME datarefs that breaks.

It depends whether you're considering your primary navigation mean is the GPS, not the NAV radio, and therefore, having the distance from the GPS is expected.

Update: I've been reviewing a number of docs and I fail to find whether the GTN could actually interface a DME equipment so that it actually synthesized the DME signal for the DME indicator to display the GPS distance as-if it was a DME radio signal. Some of the information shows it is actually possible but some other leads me to think the information displayed would only be from the NAV radio signal, not from the GPS.

I believe the X-Plane default GPS also overrides the DME radio data with GPS data but this would need to be verified. I guess adding a DME option makes sense in this case, as this will further add optional integration capabilities depending on the specific aircraft coding the simulator.

Edited May 18, 2020 by RXP

[russgreen 1]

Toggling the CDI source on the built in GNS doesn't change the DME. The DME still reads from the beacon tuned in the nav radio. 

[russgreen 1]

12 hours ago, RXP said:

I guess adding a DME option makes sense in this case, as this will further add optional integration capabilities depending on the specific aircraft coding the simulator.

Yes sounds like this solves my issue and still support the type of integration you were going for.#

Many thanks

[russgreen 1]

Just wondering if you have an ETA for when this fix might be available.

Many thanks

[RXP 2,336]

Hi,

There is no ETA yet for this new feature (not really a fix) but we're working alongside many other changes going on in XP11.50 beta (from beta1 to beta 17 then RC1 etc...) The latest for our next update will be when XP11.50 final is released, we're trying sooner.

However, please understand there is no granularity for DME in XP11. Whenever you override the NAV needles, you also have to override the DME value otherwise it is not updated by XP11 anymore. This means whenever your Link the HSI and/or the VOR to the GPS you'll loose DME from NAV radios. This is the reason the GTN/GNS V2 are updating the DME value as well otherwise you'd get distracting false indications.

Edited August 19, 2020 by RXP