Real DME

tomerh · 13 Oct 2012

Hi,

In real cessna's DME there is independent radio frequency you can set for getting DME range.

for example:
NAV1 set to 113.5,
NAV2 set to 112.4,
DME set to 112.8,

I want to develop, bendix king DME with frequency dial but FSX core have only 2 nav radio.. there is no NAV3....

any suggestions?

JB3DG · 13 Oct 2012

I suppose one could fake it if you had a table of all VOR/DMEs, their frequencies and locations....Using frequency you could find the desired DME and then using a bit of math determine your distance from it and then fake the ground speed/ETE returns etc...

rpmc · 13 Oct 2012

tomerh said:
I want to develop, bendix king DME with frequency dial but FSX core have only 2 nav radio.. there is no NAV3....

any suggestions?

Hi,

To build something like the KN 62 or KN64 DMEs, then you need to effectively create a NAV3 for that stand-alone DME, but you're right... FS limits you to two NAV radios.

Naruto-kun has the right approach, but if you're willing to learn a little about the gps module, then that's the way to access the database with all the navaid information. There are several steps to the process:

1. Nearest VOR search.
2. After the search concludes, find the index number for the VOR whose frequency matches what you dialed into your DME gauge
3. Set NearestVorSelectedVor to that index number
4. Set NearestVorSelectedVorLatitude, degrees >L

MELat, degrees
and NearestVorSelectedVorLongitude, degrees >L

MELon, degrees
5. Then use GeoCalc for distance:

A

LANE LATITUDE > GeoCalcLatitude1, A

LANE LONGITUDE > GeoCalcLongitude1
L

MELat > GeoCalcLatitude2, L

MELon > GeoCalcLongitude2
GeoCalcDistance >L

MEDistance .. and you display that in your DME gauge.

Use GeoCalc for distance rather than NearestVorCurrentDistance so you do not have to repeat the time-consuming NearestVor search to get real time distance readouts.

The ground speed and minutes for your DME gauge are then calculated in your code with basic arithmetic.

It looks intimidating especially if you have not done much with the gps before, but this approach is accurate, efficient, and the way to go.

Bob

n4gix · 13 Oct 2012

Most modern VHF avionics radios have the UHF DME transceiver built in. The DME frequencies are paired with tuned VHF stations automatically, so no separate "tuning" of a DME frequency is required.

See: http://en.wikipedia.org/wiki/Distance_measuring_equipment

In the case of older VHF avionics radios, a separate DME transceiver and digital display is connected to data buss of the NAV radio(s) to obtain the tuning information. There is no separate tuning knob. In other words, it is not a "NAV3" at all!

See: http://www.allstar.fiu.edu/aero/DME.htm

Certain DME radios have a frequency-hold function. These radios are channeled by the primary VHF navigation radio. When the pilot selects the VOR frequency, the DME also channels. The DME hold function retains the frequency of the original VORTAC station on the DME while the pilot channels the VOR receiver to another frequency.

That is precisely why FS9/X provides the DME distance automatically if the VOR, Localizer or ILS tuned has a paired DME transceiver co-located. The one function FS9/X does not support is the above mentioned "DME Hold" feature. For that, one might be able to "fake the feature" using the technique Bob suggested (GPS query).

Given that FS9/X has no UHF capabilites at all, and that every VHF NAV frequency selected auto-tunes the DME frequency pair, it is a completely transparent process to the pilot. This is true for both sim-life and real-life usage.

rpmc · 13 Oct 2012

n4gix said:
The one function FS9/X does not support is the above mentioned "DME Hold" feature. For that, one might be able to "fake the feature" using the technique Bob suggested (GPS query).

Right... that's the solution for the KDI572 DME Hold, and in that case, the gps search uses (A:NAVX IDENT, string) to get at the VOR lat and lon. The rest is the same ... GeoCalc for distance and arithmetic for GS and Mins. It works well if you remember to deal with duplicate Ident returns.

But, I am pretty sure that the old KN62A and KN64 had their own frequency tuning capability.... hmmmm, is that not right?

Bob

jeroen79 · 13 Oct 2012

I saw this in an addon aircraft: Use another radio for the DME.

When the DME hold is not engaged the extra radio's frequency is slaved to the main radio's frequency, so it will be tuned to the same station.
When DME hold is engaged the extra radio is no longer slaved to the main radio and it will stay at it's current frequency.
The DME gauge is then setup to use the extra radio instead of the main radio.

A possible complication is that this aircraft had only one main nav radio and the second radio was the DME radio.
I don't know if FS allows more than two radios but if it doesn't then this will not work on an aircraft with more than one nav radio.

rpmc · 13 Oct 2012

jeroen79 said:
.
I don't know if FS allows more than two radios but if it doesn't then this will not work on an aircraft with more than one nav radio.

Jeroen - We're limited to two NAV radios, so you're right that it won't work if your a/c already has 2 NAVs and you want to keep it that way.

tomerh - Making a NAV3 is a difficult thing to do for anyone new to gps. Maybe you are not one, but for those that are, here's a working solution. It's just the basics to show the approach.
The Nearest VOR search is triggered by the Mouse action at the bottom:

Code:

<Update>
(L:NrstVORSearch, bool)	
	if{
		100 (>C:fs9gps:NearestVorMaximumItems, enum) 
		200 (>C:fs9gps:NearestVorMaximumDistance, nmiles)		
		(A:PLANE LATITUDE, degrees) (>C:fs9gps:NearestVorCurrentLatitude, degrees) 
		(A:PLANE LONGITUDE, degrees) (>C:fs9gps:NearestVorCurrentLongitude, degrees)
		
		(@c:NearestVorItemsNumber) s2 0 != 
			if{
				:100
				(L:LoopCounter, enum) ++ (>L:LoopCounter, enum)
				(L:LoopCounter, enum) (>C:fs9gps:NearestVorSelectedVor)
				(C:fs9gps:NearestVorSelectedVorFrequency, mHz) (L:DMEFreq, number) ==	
				(C:fs9gps:NearestVorSelectedVorType) 1 &gt; and
					if{  														
						(C:fs9gps:NearestVorSelectedVorLatitude, degrees) (>L:SelVORLat, degrees)
						(C:fs9gps:NearestVorSelectedVorLongitude, degrees) (>L:SelVORLon, degrees)	
						g200								
					} 					
				(L:LoopCounter, enum) l2 &gt;= if{ g200 }	
				g100
				:200
				0 (>L:NrstVORSearch, bool)
			}				
	}	

(A:PLANE LATITUDE, degrees) (>C:fs9gps:GeoCalcLatitude1, degrees) 
(A:PLANE LONGITUDE, degrees) (>C:fs9gps:GeoCalcLongitude1, degrees)			
(L:SelVORLat, degrees)	(>C:fs9gps:GeoCalcLatitude2, degrees) 
(L:SelVORLon, degrees)	(>C:fs9gps:GeoCalcLongitude2, degrees) 

(L:DMECycleCounter) ++ (>L:DMECycleCounter)
(L:DMECycleCounter) 36 ==
	if{
		(L:DMEDistance, number)	(>L:DMEDistanceOld, number)
		(C:fs9gps:GeoCalcDistance, nmiles) (>L:DMEDistance, number)		
		(L:DMEDistanceOld, number) (L:DMEDistance, number) - (P:ABSOLUTE TIME, seconds) (L:AbsoluteTimeOld, number) - / 3600 * (>L:DMEGroundSpeed, knots)
		(P:ABSOLUTE TIME, seconds) (>L:AbsoluteTimeOld, number)
		(L:DMEDistance, number) (L:DMEGroundSpeed, knots) / 60 * (>L:DMEArrivalTime, minutes)				
		0 (>L:DMECycleCounter)
	}
</Update>

Code:

<Area Name="Nearest VOR Search" Left="0" Top="685" Width="15" Height="15">	
	<Cursor Type="Hand"/>
	<Click Kind="LeftSingle">
		-1 (>L:LoopCounter, enum)
		1 (>L:NrstVORSearch, bool)
	</Click>
</Area>

The L:Vars that you use with your gauge are DMEDistance, DMEGroundSpeed and DMEArrivalTime. DMEFreq is the frequency measured in mHz that you tune your DME gauge to.

If you're making a KN62 or KN64 for example, then setting the function switch to RMT will cause the DME to read from either NAV1 or NAV2, so you might want to code it that way. If the function switch is set to FREQ, however, then you use the frequency tuning knobs on your DME to set the VOR frequency you want and then launch the Nearest VOR search shown above.

The gps variables used for this are FSX variables. If using FS9, it's a little more complicated, but still very do-able.

Cheers,

Bob

tomerh · 15 Oct 2012

thanks alot bob, I new to GPS but I'll try this code

kevintampa5 · 16 Oct 2012

tomerh said:
Hi,

In real cessna's DME there is independent radio frequency you can set for getting DME range.

for example:
NAV1 set to 113.5,
NAV2 set to 112.4,
DME set to 112.8,

I want to develop, bendix king DME with frequency dial but FSX core have only 2 nav radio.. there is no NAV3....

any suggestions?

This totally depends on the owner's comm/nav setup. If using the original equip pre 90's, then yes they did. Most built after did not include the separate dme guage as the nav1 and some nav2 usually had that capability.
I currently fly a 1977yr c172. It had 1 bendix comm radio, 1 avidyne comm radio, 1 garmin 190 gps ( i think 190 may be mistaken) that had a bunch of orange lines to indicate airspaces and orange specs for fixes. Used a white line to indicate traveled path and if I recall a thick white or red line for the path to follow. the nav 1/2 were some offshot company i cant remember the name of. Both were tuned through the gps, but were contained seperate from the gps. Took a little getting used to but it worked well. it used the gps to readout the dme, even if the gps was never initiated after startup.
There was no ADF or DME only readout guage. LORAN was capable in it, but that was removed a few years ago.
I flew a 152 back in 2002 that had a key click handheld microphone. had no mic out port for a headset, but had ear out.