Re: [Flightgear-devel] fgmap navaids

[Ron J. <wi...@je...>]

On Fri, 2006-06-02 at 14:17 +0100, Vivian Meazza wrote:

Hi Vivian

> I'm more than willing to be corrected on this one, but my understanding is
> as follows:
> 
> A VORTAC station has 3 frequencies in RL - TACAN, VOR, and DME.

This is my understanding, too.  Further A TACAN "channel" includes 3
frequencies, Two for TACAN/DME and one for VOR/ILS. [1]  

>  In FG nav.dat only the VOR and DME are held.

Actually, nav.dat only holds the VOR freq. The DME uses the associated
VOR frequency. 

>  Thus it is a fix in the case of VORTAC to misalign the TACAN channel/frequency
> pairing to the VOR frequency in stead of the TACAN frequency.

There is not a mis-alignment.  The TACAN spec includes the VOR freq
pairing, as well as the DME freq pairing.  It is possible in real life
to tune a VOR/DME reciever to (most?) TACAN stations and receive DME
information.  

>  Unfortunately, there are other stations in
> the world which are TACAN only, which seem to have the correct TACAN
> frequency assigned: Flesland TACAN is one such example.

Flesland TACAN (FLE) uses channel 092X [2]
Flesland VOR/DME (FLS) uses channel 102Y (115.55 MHz) [3] 

zgrep Flesland nav.dat.gz:
12  60.300036  005.213589    185 11450 130   0.000 FLE  Flesland TACAN
12  60.311261  005.212194    213 11555 130   0.000 FLS  Flesland VOR-DME


Under the current version of TACAN.dat FLE is tuned using 058Y and FLS
is not tuneable.

FLS should give DME only to the onboard TACAN system, currently the
TACAN system in FG would ignore it, if it were tuneable, I think.

>  Thus we fix the VORTAC at the expense of the TACAN.

I don't see this.  With a corrected TACAN.dat and the current nav.dat
both VORTAC and TACAN work fairly well.  I use HIF TACAN all the time:

12  41.120503 -111.963681   4806 11120  40   0.000 HIF  Hill TACAN


>  The correct fix is to modify nav.dat to show all 3 frequencies for the VORTAC stations.

If I understand correctly, you are concerned because the current TACAN
uses the name of the DME station to determine whether or not to provide
TACAN service.  Adding a section for TACAN Azimuth that mirrors the DME
entries for VORTAC and TACAN stations makes sense, the TACAN DME would
respond to all DME entries (12/13) in nav.dat and TACAN azimuth would
respond only to the new (number??) TACAN entries in nav.dat.  

Overall, I don't see a way to proceed without first replacing TACAN.dat.





[1] http://www.vectorsite.net/ttradar5.html#m3
[2] http://worldaerodata.com/wad.cgi?nav=FLESLAND&nav_id=FLE&nav_type=3
[3] http://worldaerodata.com/wad.cgi?nav=FLESLAND&nav_id=FLS&nav_type=4