TACAN measuring distance from a DME?

[Fresh]

Hi,

maybe someone who has used a TACAN for real can clarify something for me:

I know that TACAN and DME are basically similar when we are talking about the distance measuring aspect. So I would like to know if a VOR/DME station (without a co-located TACAN), which is working on a frequency of, let's say, 114.85 Mhz (that would be the VOR part) has a channel pairing of 95X (Xmit on 1119 Mhz, Recv on 1056 MHz - see attached file).

Can a fighter, with TACAN equipment, tune 95X, and receive the DME distance from the civilian VORDME station 114.85?

I have tried with the F/A-18 on the South Atlantic map, and with the F/A-18 on the Caucasus map, no success.. so either TACAN can't see VORDME stations, or it is not modelled in DCS, or the DCS F/A-18 can't do it.

Does anyone have any answers/thoughts to this?

Thanks in advance,

 

Fresh

p.s. I tried the F-5E as well.. no luck. Check out the VORDME near Kutaisi (KT on 113.6 MHz, with co-located DME on channel 83X) - TACAN set to 83X doesn't display any distance.

VOR-Frequencies-to-TACAN-Channel-list.pdf

Edited February 6, 2023 by Fresh

[Nealius]

This came up a few months ago in one of the terrain subforums but I can't find the topic. I think the general concensus was that VOR/DME-TACAN pairing wasn't modeled in DCS. I have fuzzy memory that one or two modules may have it modeled individually, though. 

Edited February 9, 2023 by Nealius

[Nickelmouse]

Fun fact: VOR/DMEs with paired TACANs are called VORTACs

Edited February 9, 2023 by Nickelmouse

[some1]

There are multiple issues with DME on DCS maps. IIRC it was all reported at one time or another, but fixing it is not a high priority.

-using DME component of a VOR/DME navaid with a TACAN radio - doesn't work

-using DME component of a VOR/DME navaid with a VOR radio (like C-101CC) - also doesn't work

-using DME component of a ILS/DME navaid - doesn't work because these don't exist in DCS at all, while in the real world this is the most common type of ILS installation at the airports. 

The last issue makes it impossible to fly almost any real world ILS approach in DCS. Most of them use ILS/DME and require ability to measure distance from ILS.

 

null

 

Edited February 9, 2023 by some1

[Fresh]

Thanks everyone for your responses!  So I guess it will stay like that.. at least I won't waste time trying anymore!

Have a nice weekend!

Fresh

[ThePops]

On 2/9/2023 at 9:49 AM, some1 said:

There are multiple issues with DME on DCS maps. IIRC it was all reported at one time or another, but fixing it is not a high priority.

I have never really paid attention until lately. On the Kola map, the rule seems to be that everything navaid is a complete mess on all newly added airports, and doesn't get fixed until 1-2 updates later. It's really hard to understand why this is so, because all information needed about navaids is official and correct, and freely available in the AIPs. Anyway, reporting all these bugs, the issue about DME pops up. AFAIKS DME is simply not there at all (other than as part of the TACAN).

The DME part of either a VOR/DME, DME/DME or TACAN should be available for both civilian and military aircraft.

Perhaps a part of this is due to the fact that this is a bit messy also in real life ? NDBs have almost completely disappeared from everywhere, and ILS's are disappearing as well. De facto standard for precision approaches is today RNP (basically GPS, but it's a bit more to it than that). In a GA aircraft there are no longer any need for anything radio based when flying IFR. All that is needed is a GPS (Certified navigation piece, made by Garmin typically  ). For commercial flights (airlines mostly) it a bit more nuanced. Here some kind of backup system and/or redundancy is a real issue, and the trend is to install more DMEs. DME/DME is much better and cheaper than a couple of NDBs. This is seen everywhere. NDBs are removed, DMEs are installed.

A good example is Andøya (on the Kola map). It has no ILS, thus no precision approach it seems. This is of course not correct. Looking in the AIP, the precision approaches are RNP. RNP for RW 14 and RNP for RW 32. RW 14 also has LOC and VOR approach, while RW 32 only has VOR. These are all non precision approaches (for good weather), but the thing is, the requirement for all of them is DME. They cannot be flown without DME. The same goes for ILS anywhere. Today the DME is an intrinsic part of any ILS. A long time ago there were marker beacons, but these are long gone for most of it. Andøya has 3 DMEs, only one of them exists in DCS.

DME is like a part of the plumbing that no one sees. Kind of ancient technology, overshadowed by ILS and later RNP/GPS, ADS-B, WAM and whatnot. The fact is that no larger airport would today be operational without DME, and the trend is more DMEs not less. DME should definitely be modelled in any map that is supposed to be contemporary IMO.    

[some1]

1 hour ago, ThePops said:

Perhaps a part of this is due to the fact that this is a bit messy also in real life ?

It is not messy in real life. All the existing navaids with their locations and frequencies are available online for free from the respective AIPs. For example here's Norway (enroute are in part 2 ENR 4, landing navaids are in part 3 of the document, separate for each airport).

https://ais.avinor.no/no/AIP/View/136/2025-01-23-AIRAC/html/index-en-GB.html

Obtaining historical data is more difficult, but since the maps in DCS represent modern times, this is not a big problem.

The problem is that DCS developers do not know, or do not care about the issue. 

Edited January 26 by some1

[ThePops]

1 hour ago, some1 said:

It is not messy in real life

I think it is. It's not due to lack of info, but rather that the info changes a lot. This is especially true in the last 10 years approximately, when RPN was introduced "for real", although some places here and there got it earlier. This also lead to other changes. IFR was for a long time (several decades) about VOR, NDB, ILS and radar guidance, and it was the same for GA, airliners and military. The military also had TACAN of course, but it was nothing but a parallel VOR/DME system, and still is.

Today the situation is more like:

• GA: A dedicated aviation GPS is all you need, both for enroute and approaches. Lots of older planes also have ILS/VOR and DME, even ADF. Today you cannot even get ADF for GA at a price anyone is willing to pay. ILS/VOR/DME is for special purpose or special interest (special purpose here includes obtaining the IFR rating, it's really old fashioned). A typical GA airport will have no radio navigation at all. All IFR is GPS based.
• Airlines: They got it all of course, according to airspace requirements and specific internal airline requirements, but since precision approaches are RPN, this will be used most of the time.
• Military: Don't know what exactly the F-35 has for instance, but any military aircraft also haveto be able to use the airspace in peace time. I would think it's very much like Airlines, GPS and INS rules, but I would be surprised if ADF was very common for instance.

The point though, is that while VOR, ILS and ADF (NDB) is on the way out, very slowly in some cases, DME is not. That is, it's already gone in GA, but not likely to disappear at all. Stand alone DME stations are popping up.

DCS is not about navigation of course, and I'm sure not many people will notice if DMEs are missing (I wasn't until Kola). It's just a bit odd though that the fundamental ABC of aviation does not even exist and at the same time people are urging for "high fidelity realism". Personally I'm more in the "get the basics right" category if I had to chose between a nice cockpit and correct approach procedure.

[ThePops]

On 2/9/2023 at 9:49 AM, some1 said:

-using DME component of a VOR/DME navaid with a TACAN radio - doesn't work

-using DME component of a VOR/DME navaid with a VOR radio (like C-101CC) - also doesn't work

Just tried several with the C-101EB (because it well set up with avionics). It looks like using DME component of a VOR/DME does indeed work at some stations. I tried only on Kola map due to easy access of AIP, in the west at least  I think perhaps this is more of an implementation issue on the map itself. Perhaps also on the aircraft? A big mess for sure.

[some1]

Yep, it looks like VOR/DME issues have been fixed at some point in the last few years since I made that post. I checked a VOR/DME station on PG map and DME works there using TACAN radios. So if you have a VOR/DME on a map, you should be able to receive the distance on a Tacan radio if you dial the corresponding channel.

Unfortunately a standalone DME like Paphos (108.90) here on Syria map does not seem to work. And we still don't have an ILS/DME navaid type defined in the sim, so most real world approaches can't be flown. 

Looks like here the map developer attempted to recreate ILS/DME setup by manually placing a DME near the runway threshold, on the same frequency as the Localizer. Except it's only on a single airport, and it doesn't work anyway.

[buur]

tried to add the channels into Syrias beacon.lua, but no luck.

Neither DME nor ILS distance

[ThePops]

With navaids there is a clear, and very important, difference between the physical ground based navaids and the instruments in the cockpit with their inherent merging, added calculations and so on of these navaids into much more abstracted navigation aid. The FMS in airliners is the state of the art today. It combines everything (GPS, INS, DME, VOR, ILS and so on) into an opaque and abstract navigational solution, by merging signals from all these technologies. Earlier/older instruments did bits and pieces of this merging and abstraction. A basic old fashioned "ILS instrument" is also a rudimentary merging and abstraction of usually 3 completely separate technologies (LOC, GP and DME. In very old versions the DME is replaced with marker beacons). The instrument itself can be seen as one single entity.  

The basic principle today is that GNSS is the primary instrument, while INS is the secondary/complimentary instrument. As an always working backup (GPS can be jammed and spoofed), there are only two acceptable solutions. One is VOR/DME, the other is DME/DME. The backup for precision approaches is ILS, but only with DME. Thus DME is essential. Without it, all commercial airliners would be grounded, with some exceptions.

VOR/DME works basically as a TACAN. DME/DME use multilateration, all done by the FMS. Two DME stations are enough. The FMS finds out all by itself what stations and what kind of stations it uses at any given time. It would use DME/DME most of the time, but add a VOR station every now and then for instance, or use only VOR/DME for a period of time. All based on error estimation and available stations.

The point is, there is no such thing as a VOR/DME "signal" or "station", in the same manner as there's no DME/DME signal or station. DME/DME is at least 2 separate stations obviously, and they are far apart. The output from the FMS is the same if it uses VOR/DME or DME/DME, or VOR/DME/DME for that matter, or GNSS (to some degree).

A TACAN station has bearing and distance functionality. The bearing is similar to a VOR in overall functionality, but the distance technology IS a DME. There's no difference. It is the same thing. The main point here is that a DME is a separate thing. It's not "part" of any other station. It's not "part of" a TACAN (even though this usually is the case) or "part of" an ILS or a LOC or a GP or whatever. It's a completely separate entity, and DMEs are often installed as standalone units. A DME "for an ILS" may be used more often by FMS's doing RNAV than it is used for ILS approaches. The "part of" is a misconception, probably due to the way aircraft instruments are merging and abstracting for instance a VOR/DME or an ILS.

Another reason for this misconception is perhaps the organization of frequencies/channels for all these technologies. This organization can be seen in the large table at the bottom here: https://wiki.radioreference.com/index.php/Instrument_Landing_System_(ILS)_Frequencies and is well known to most here I think. It is used both for instruments and for frequencies for ground channels. In an aircraft, when the ILS is tuned in to 109.10, what happens is:

• The LOC frequency is tuned to 109.10, this is done manually
• The GP is automatically tuned to 331.4
• The DME is automatically tuned to channel 28X or (1052 - 989)

Obviously the ground equipment must also use these frequencies for that runway, or this wouldn't work. In civilian aircraft the GP and DME are usually never tuned to a channel as such. The GP is tuned automatic from the LOC frequency. The DME is tuned automatically from the VOR or LOC frequency. DME isn't used much in GA anymore, but the way a standalone DME was tuned was not usually by the channel, but by the corresponding VOR/LOC frequency. There are 200 VOR+LOC frequencies. There are 252 TACAN channels. The military has access to more channels than a civilian aircraft normally has. An FMS will tune the DMEs to whatever it thinks gives the best navigational solution without the pilot knowing anything.

In that sense I think the beacons.lua files are a bit odd compared with the real world. I can understand TACAN, since this is two technologies merged into one complete system. For everything else, all that is needed is DME, LOC, VOR and GP as standalone units. A VOR/DME is simply a VOR + a DME. Any version of ILS can be made by combining LOC + DME and eventually GP, or no DME but marker beacons. There's no need to have a separate VOR/DME and a separate ILS with DME (with obscure channels), and one ILS without DME and so on. It's a pity the DME in DCS don't work. It renders almost all ILS'es useless. There are NDBs also, but that's really ancient.

Then there's the Russian system which I know nothing about