VOR signal demodulation ?
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VOR signal demodulation ?
Dear Techies,
I'm looking for an explanation how a VOR signal is made up and how it is demodulated in the receiver.
In my JAR-FCL course there is only the basic explanation, which is fare enough for pilots, of a ref signal and vari signal, they don’t mention the sub carrier of 9960Hz superimposed with 30Hz or the demodulation process, which is of particular interest me.
Please can someone explain in detail (I’m reasonable good with RF) the ins and out of the signal itself.
Cheers,
LL
I'm looking for an explanation how a VOR signal is made up and how it is demodulated in the receiver.
In my JAR-FCL course there is only the basic explanation, which is fare enough for pilots, of a ref signal and vari signal, they don’t mention the sub carrier of 9960Hz superimposed with 30Hz or the demodulation process, which is of particular interest me.
Please can someone explain in detail (I’m reasonable good with RF) the ins and out of the signal itself.
Cheers,
LL
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DVOR signal
Hi,
Thank you for the explanation. I would appreciate some diagrams via email, if you could give me your email address then we could discus this topic that way.
I also have a problem understanding how the 9960Hz upper side band is separated and put onto e.g. ant number 1 and the lower side band put onto antenna nr 25 at the same time. How are the side bands split in the transmitter and distributed to the antennas ?
I thought the signal whizzing around on the circular antena array was the vari signal and the ref would be the one in the middle in the system ?
Cheers once again,
LL
Thank you for the explanation. I would appreciate some diagrams via email, if you could give me your email address then we could discus this topic that way.
I also have a problem understanding how the 9960Hz upper side band is separated and put onto e.g. ant number 1 and the lower side band put onto antenna nr 25 at the same time. How are the side bands split in the transmitter and distributed to the antennas ?
I thought the signal whizzing around on the circular antena array was the vari signal and the ref would be the one in the middle in the system ?
Cheers once again,
LL
Last edited by Liquid Lunch; 7th Aug 2002 at 08:46.
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Err, That's not quite right ASFKAP.
The VOR system works in a similar way to a Transponder (finish reading the explanation before arguing) in that there are actually 2 transmissions, 1 omnidirectional and the other, directional and rotating at a rate of 30 rotations per second. The rotation of the directional signal creates in effect an amplitude modulated signal of 30 Hz.
The omnidirectional signal contains the ident, AM modulated at 1020 Hz and a 9960 AM sub-carrier which is in turn frequency modulated +/- 480Hz at a 30 Hz rate. This is the reference phase.
The directional signal is un-modulated, it only appears to be amplitude modulated at the receiver due to its rotation (i.e rising and falling of signal creates AM effect). This is the variable phase.
The purpose of the 9960Hz sub-carrier is to keep the variable and reference phases separate within the Rx until the descriminator.
On arrival at the a/c Rx the signal is demodulated (AM) and the 1020Hz sent to the audio ccts. The 9960 is sent to an FM detector (and its 30 Hz componant extracted and sent to a counter cct) and the 30Hz AM signal is sent also to the counter.
The reference starts a clock in the counter and the variable phase stops it. The total count being a measure of the angular phase relationship between the two signals (think of the counter as a modern phase descriminator).
The counter o/p is fed to a microprocessor which produces sine and cosine o/p of the VOR bearing, which are then fed to a/c circuits.
Hope this helps.
The VOR system works in a similar way to a Transponder (finish reading the explanation before arguing) in that there are actually 2 transmissions, 1 omnidirectional and the other, directional and rotating at a rate of 30 rotations per second. The rotation of the directional signal creates in effect an amplitude modulated signal of 30 Hz.
The omnidirectional signal contains the ident, AM modulated at 1020 Hz and a 9960 AM sub-carrier which is in turn frequency modulated +/- 480Hz at a 30 Hz rate. This is the reference phase.
The directional signal is un-modulated, it only appears to be amplitude modulated at the receiver due to its rotation (i.e rising and falling of signal creates AM effect). This is the variable phase.
The purpose of the 9960Hz sub-carrier is to keep the variable and reference phases separate within the Rx until the descriminator.
On arrival at the a/c Rx the signal is demodulated (AM) and the 1020Hz sent to the audio ccts. The 9960 is sent to an FM detector (and its 30 Hz componant extracted and sent to a counter cct) and the 30Hz AM signal is sent also to the counter.
The reference starts a clock in the counter and the variable phase stops it. The total count being a measure of the angular phase relationship between the two signals (think of the counter as a modern phase descriminator).
The counter o/p is fed to a microprocessor which produces sine and cosine o/p of the VOR bearing, which are then fed to a/c circuits.
Hope this helps.
