VHF comm frequencies in virtual ATC

[Hardy Heinlin]

Good evening,

there are at least two ways for programmers to associate a radio channel with a frequency value:

- Use the frequency value displayed on the tuning panel.

- Use the frequency value which is actually transmitted.

Example:

When the tuning panel indicates 118.015, the transceiver sets 118.017. The display never shows 118.017, it rounds the value up or down to the next 5 or 0.

What kind of frequency values are used and required in Internet ATC simulations, e. g. at VATSIM etc.?

Thanks,

|-|ardy


P.S.: I guess they don't go that far and use 0.33 and 0.66 kHz fractions.

[Jeroen Hoppenbrouwers]

There was a long-standing problem that VATSIM software still used the 25 kHz grid, while the real world was switching to 8.3 kHz. Many real-world frequencies simply could not be tuned in VATSIM. I'm not even sure this has changed by now.

In any case, there is a strict rule that the DISPLAYED frequency is what is used. Because only this one is the common reference, on paper and on equipment. So you don't need to work with "exact" frequencies internally; just follow the standard grids.

My old SquawkBox747 used a sneakily modified grid that was 8.33 but with rounded values to match up exactly with the 25 where needed. This still worked one year ago when we used SB747 as panic backup during UK WorldFlight. I have no reasons to assume anything changed since then.

Code Select Expand


  # The following is a list of legal decimal tuning figures. It has
  # been modified to merge the 25kHz grid into the 8.33kHz grid, while
  # retaining visible compatibility with 25kHz 2-digit tuners.
  set FREQS {000 010 015 020 035 040 050 060 065 070 085 090
             100 110 115 120 135 140 150 160 165 170 185 190
    200 210 215 220 235 240 250 260 265 270 285 290
    300 310 315 320 335 340 350 360 365 370 385 390
             400 410 415 420 435 440 450 460 465 470 485 490
    500 510 515 520 535 540 550 560 565 570 585 590
    600 610 615 620 635 640 650 660 665 670 685 690
    700 710 715 720 735 740 750 760 765 770 785 790
    800 810 815 820 835 840 850 860 865 870 885 890
    900 910 915 920 935 940 950 960 965 970 985 990}


Actually this code is now in the GoFlight Bridge, so still 100% functional and maintained.

[Hardy Heinlin]

OK, thanks.

...

Is it possible in VATSIM etc. to communicate with two controllers using two different frequencies at the same time, from the same aircraft? I'm asking just out of interest (PSX models three independent VHF systems anyway).

|-|

[Jeroen Hoppenbrouwers]

Normally not, though technically the possibility is present in the underground infrastructure.