Reception distance for VOR

[Let410]

The formula is
Distance= 1.25×(square root)height of tower

Question: you are at 3800ft, the tower is at 900ft. What is the reception distance?

Two things: first. I have always been taught the formula above. In recent study notes it show 1.23 not 1.25.
Secondly. Sometimes one uses only the aircraft height, sometimes aircraft height and tower height and also the difference in heights

Could someone please clarify for me. I may have missed something.

P.S. sorry about the way the formula was written.

[daedalusx]

It's 1.23 sqrt of height. And obviously it's the difference between the AC height and the antenna. If you're flying at 10 000' ASL and the Antenna is at 8000' ASL then your reception distance would be 1.23 sqrt*2000

[co-joe]

1.25 is for company routes off airway to figure out MEA. Adds a bit of a fudge factor.

[Let410]

Thanks

[photofly]

It's 1.23 sqrt of height. And obviously it's the difference between the AC height and the antenna. If you're flying at 10 000' ASL and the Antenna is at 8000' ASL then your reception distance would be 1.23 sqrt*2000

Actually it's not obviously the difference between the AC height and the antenna. It depends on what the terrain between the AC and the antenna looks like.

If the antenna is on a hill, and the terrain in between goes down to sea level, then it's actually 1.23 * sqrt (antenna height) + 1.23 * sqrt (AC height). Putting the antenna high on top a hill doesn't decrease the range but increases it - which is why they do it.

Here's a diagram:

hill.png (94.33 KiB) Viewed 10036 times

And If the terrain between the antenna and the aircraft is higher than the antenna height, then it's less than the 1.23 * sqrt (AC height - antenna height.)

[ThatArmyGuy]

There's an error in your diagram.

The Earth is flat.

[Zaibatsu]

Also, nobody cares.

[photofly]

I suspect the person who wants to get the right answer in their CPAER test cares.