Talk:Difference in the depth of modulation

This article was nominated for merging with Instrument landing system on May 2012. The result of the discussion was No merge.

Calculations[edit]

The numbers 0.00145% per metre and 15.5% full-scale-deflection seem a bit odd - wouldn't that imply that the localiser beam is 21km wide? 80.177.58.134 (talk) 15:29, 31 July 2009 (UTC)[reply]

The use of the % sign may be slightly misleading in this case. 0.00145% is intended to be a percentage index (for want of a better name) and 15.5% is shown as a normal percentage. The calculation you are trying to do would work if you used the percentage index of 0.155 instead of 15.5%. You should get a localiser course sector width of 213 meters (700ft) at the ILS reference datum (runway threshold). --Spuzzdawg (talk) 09:24, 12 October 2011 (UTC)[reply]

Not. I will come back and edit the page some time if someone doesn't get to it sooner. Localizer widths vary by installation -- most ILSs are 5 degrees wide, some are wider. ICAO Annex 10 specifies that the DDM is 0.155 for a full scale deflection, which is the maximum angular difference from centerine the operators of the localizer want you to fly. Normally this equates to a number of meters error at the runway threshold but not always. Depth of 90 Hz modulation + depth of 150 Hz modulation is usually around 40%. 0.155 (or 15.5%) DDM means that one of the tones is at 12.25% mod and the other is at 27.75% which should create exactly full scale deflection on the CDI. How wide the sectors are depends on local requirements. Altaphon (talk) 19:23, 19 July 2014 (UTC)[reply]

"Depth of modulation"?[edit]

that vary linearly in the depth of modulation

What exactly does "depth of modulation" refer to? Is it the strength (amplitude) of the modulating signal? AxelBoldt (talk) 02:19, 10 March 2010 (UTC)[reply]

LOC and GS each use two sector beams of the same RF frequency but different modulating frequencies. DDM is the difference in strength of the two modulating signals between the two beams, which are received simultaneously. Altaphon (talk) 19:26, 19 July 2014 (UTC)[reply]

Merge[edit]

I don't think this should be merged with the ILS article, but linked to from it. DDM is a separate concept. Altaphon (talk) 19:26, 19 July 2014 (UTC)[reply]