Nav antenna

[vorlon1]

I guess I didn't make it clear I was kidding about the speed increase, but I am serious about asking if anyone has flipped the antenna. Any RF engineers out there? What I don't know about radio signals would fill a book or two. 

(J/K)

[Yetti]

2 hours ago, vorlon1 said:

I guess I didn't make it clear I was kidding about the speed increase, but I am serious about asking if anyone has flipped the antenna. Any RF engineers out there? What I don't know about radio signals would fill a book or two. 

(J/K)

Might want to read about horizontal and vertical polarization of radio waves.   I am not an gineer, but put myself through college installing two way radios.    Seems like the aluminum tail would shade half the signal when the ground station is off to the side.  I think the cessna install is on top of the vert stab.

[PT20J]

VOR, localizer and GS are all horizontally polarized - that’s why the dipole antenna spreads out horizontally. The blade and towel bar style antennas are split on each side of the fin. So, it probably works fine to reverse it. Still, the is no way to be sure without doing it and then measuring the change in antenna pattern. There must be some reason Mooney mounted it the way it did and it would be good to know that.

[Yetti]

As I recall the vor transmits a set of tones for each radial.   So as long as the antenna is horizontal and one side can hear the tone, it should work.   Check to see if there is a thru hull bnc on the pilot side inspection port in front of movable tail joint down low.

Edited February 3, 2019 by Yetti

[PT20J]

It was a four course range that used tones. VOR transmits an omnidirectional reference signal and a rotating directional signal and the phase difference between the two defines the radial. The antenna is a dipole and each whisker makes up one half of the antenna. It is not two separate antennas connected together. 

[EricJ]

2 hours ago, Yetti said:

Might want to read about horizontal and vertical polarization of radio waves.   I am not an gineer, but put myself through college installing two way radios.    Seems like the aluminum tail would shade half the signal when the ground station is off to the side.  I think the cessna install is on top of the vert stab.

Shading from the tail would be the only difference, otherwise the difference would just be whether you're approaching or leaving the VOR (since that's the effect of flipping it the other way).

So it might affect the antenna pattern.  If the affect was large there would be some directions from the aircraft that would get stronger signal than others.   It would take some testing to sort out whether that's happening or not, but I assume if it was a large effect some other method would be used.

15 minutes ago, PT20J said:

It was a four course range that used tones. VOR transmits an omnidirectional reference signal and a rotating directional signal and the phase difference between the two defines the radial. The antenna is a dipole and each whisker makes up one half of the antenna. It is not two separate antennas connected together. 

The two signals (the reference and directional signal) are transmitted separately as FM and AM modulation, respectively,  so in the receiver they're separated and then the phases compared.

 

 

[Prior owner]

Ok, here’s my guess...it’s pointed forward so that the tail doesn’t shade the signal (as suggested above), and so that the fuselage doesn’t shade the signal while inbound during a localizer approach.