VOR no-Line-of-Sight reception bug

[Goblin]

? Its still just a radio signal.

 

Yes, but NDBs are normally in the KHz frequency band and the VOR is in the MHz band. The lower the frequency the better it will bounce and travel longer.

[Havner]

? Its still just a radio signal.

It's been a long time since I remembered the frequencies, but very low frequency radio waves that's been used over the world for normal radio (maybe they still are) could travel to the opposite side of the Earth because they bounced of off the upper layers of atmosphere. No LOS there. No idea whether this is the case with NDB, but physically it's completely possible.

[Xtrasensory]

HF radios require a precise tweak of the frequency used to actually succesfully go over the horizon. The usable frequency differs for each specific time during the day and enviromental conditions. Eventhough a NDB might be a shortwave frequency its still not a dedicated over the horizon beacon and requires LOS. Those few times I usee them when they were still in commision, you already got a weak and fluctuating direction at 20nm, ofcourse dependig on the power output of the station.

[Goblin]

Naturally the reception range depends on the output power of the transmitter.

If your needles fluctuate at 20NM you're probably tuning a locator...

We still have NDB here in Norway, and I can track them much farther than that.

[Xtrasensory]

Those were just regular enroute and airfield ndb's. What ranges are you tracking them and at which altitudes?

Edited January 18, 2016 by Xtrasensory

[Goblin]

We don't use them for navigation anymore, other than their position in the FMS. :)

So I can't remember specifics. I can test it tomorrow though. Scheduled on the redeye... X-/

But NDB signals are generally considered beyond LoS. Depending on the equipment of course.

https://en.m.wikipedia.org/wiki/Non-directional_beacon

[Xtrasensory]

Ah I see what you mean.

[Goblin]

I received a NDB 270NM away at 15000'. The horizon should be around 150NM away at that altitude if you use the old approximation formula of 1,23x SqRt (Alt.).

I also received an NDB 40NM away when on ground at the airport. And there' a 4000' high mountain range between me and the beacon, so no LoS there.

[Huesudo]

From the first paragraph on Wikipedia

NDB signals follow the curvature of the Earth, so they can be received at much greater distances at lower altitudes, a major advantage over VOR. However, NDB signals are also affected more by atmospheric conditions, mountainous terrain, coastal refraction and electrical storms, particularly at long range.