VOR / NAV radio: what exactly happens when you pull the ID button to listen to the morse code?

D

DCR

Pre-Flight
Joined
Jun 14, 2023
Messages
80
Display Name
Display name:
rudy
When you tune in a VOR you have two options. Pull (or push) a knob to listen to the morse code, or transmit voice over the VOR (for example if you are talking to a FSS).

One frequency, two ways to listen. How does this work? How is the morse code muted yet you can still hear other transmissions?
 
The Morse identifier is just a side signal, a channel, riding on the VOR frequency. It's a fairly common practice in radios. For instance, most public service radio stations, like your local NPR, have many channels riding their main frequency. Radio reading for the blind, for instance. Or second languages. I notice in my car that most radio stations are broadcasting text that shows up on the front of the radio (station ID, Artist and Cut being played, weather, or various messages). Same principle.
 
It's an audio frequency filter that filter in/out the frequencies that you want to/don't want to listen to. In this case, it filters our frequencies other than the frequency of the morse code tone so that the ID is more easily understood. The VOR ID is not on a separate channel or sideband.
 
Larry in TN said:
It's an audio frequency filter that filter in/out the frequencies that you want to/don't want to listen to. In this case, it filters our frequencies other than the frequency of the morse code tone so that the ID is more easily understood. The VOR ID is not on a separate channel or sideband.
Click to expand...

So if I tried to talk at the same "audible" frequency as the morse tone my voice would be filtered on a VOR voice transmission?

This might be impossible to match the tone to the level required by the filter - but lets just say I could for sake of understanding.
 
Larry in TN said:
You don't talk on a VOR frequency.
Click to expand...

I don't have an example handy (looking right now) but I was taught that you can transmit voice over some VORs to contact Flight Service.

I think I also heard some CTAFs might be transmitted over the VOR frequency but I have less confidence in my memory on that one.
 
DCR said:
So if I tried to talk at the same "audible" frequency as the morse tone my voice would be filtered on a VOR voice transmission?

This might be impossible to match the tone to the level required by the filter - but lets just say I could for sake of understanding.
Click to expand...

Take a look at the frequency box for the VOR station. Above the rectangle, if there is a frequency with an R at the end, that is telling pilots the Flight Service folks receive on that frequency. But they transmit back to you on the VOR frequency.
 
Gilbert Buettner said:
Take a look at the frequency box for the VOR station. Above the rectangle, if there is a frequency with an R at the end, that is telling pilots the Flight Service folks receive on that frequency. But they transmit back to you on the VOR frequency.
Click to expand...

Gotchya - that's what it was.

I think I was just wrong about the CTAF thing ignore that.

So in that case - if the FSS specialist had a voice which happened to be the exact same sound as the morse ID (just humor me), would their voice be filtered out unless you pulled the ID knob?
 
The IDENT is to identify the station to make sure you're tuned into the correct one and that the station is believed to be working properly. (I say "believed" because you may be the first one to find out it is not.)

So you pull the IDENT button and listen for the Morse Code to make sure you are receiving the right signal. If there is an issue with the station you will either not hear the code or it may be transmitting T E S T.
 
Years ago I was in the back seat while my wife was getting one of her primary lessons from the instructor. They were trying to track the Westminster VOR and having a lot of problems. Amusingly, they had the VOR radio turned up and I could hear the ID. After a couple of minutes of them screwing around, I had to pipe up that the thing was sending T-E-S-T. What was really stupid is my wife holds an Advanced class amateur license. She knows morse code well enough to copy that slow four letter sequence in her head with no problem. They just weren't paying attention.
 
flyingron said:
Years ago I was in the back seat while my wife was getting one of her primary lessons from the instructor. They were trying to track the Westminster VOR and having a lot of problems. Amusingly, they had the VOR radio turned up and I could hear the ID. After a couple of minutes of them screwing around, I had to pipe up that the thing was sending T-E-S-T. What was really stupid is my wife holds an Advanced class amateur license. She knows morse code well enough to copy that slow four letter sequence in her head with no problem. They just weren't paying attention.
Click to expand...

Ha I can absolutely relate. Simple things you really do know just get lost in your brain when you have a gazillion new knobs in front of you while learning "101 ways to kill yourself" doing your new hobby.
 
@DCR, yes, you are correct. This filter tech is very old and simple. The switch/knob literally switches in a small discreet circuit of a couple capacitors, inductors and resistors.

It is now done probably with digital signal processing tech and is better, but this is all simple electronic audio filters.
 
Tools said:
It is now done probably with digital signal processing tech and is better, but this is all simple electronic audio filters.
Click to expand...
My 20 year old UPSAT radios decode the ID just fine.
 
DCR said:
I don't have an example handy (looking right now) but I was taught that you can transmit voice over some VORs to contact Flight Service.
Click to expand...
You can't tune a VOR frequency on a communications radio. VOR receivers do not transmit.

You would transmit on a specified frequency, usually 122.1 IIRC, and listen on the VOR frequency. This was used when transmitters were expensive. Instead of adding an additional transmitter to the VOR station for the remote communication outlet (RCO) to FSS, they'd add a receiver tuned to 122.1 and the FSS specialist's transmission would be added to the audio transmission from the VOR. It allowed them to establish more RCOs for their given budget.

VORs used to also transmit HIWAS weather broadcasts which were a taped loops of weather updates that could be heard on the VOR frequencies. Again, this piggy-packed onto the existing VOR transmitters and provided a cost effective method of distributing weather information. HIWAS service was discontinued in early 2020.

DCR said:
So in that case - if the FSS specialist had a voice which happened to be the exact same sound as the morse ID (just humor me), would their voice be filtered out unless you pulled the ID knob?
Click to expand...
People do not speak within a very narrow frequency range. The morse code is a very specific frequency and can be easily filtered out without significantly effecting the ability to understand the voice transmission.

Remember that there are two frequencies involved. The radio frequency (RF) of the broadcast such as 114.10 Mhz and the audio frequency in the audible range, generally 20Hz - 20,000Hz, though the VOR receiver's audio frequency range would not be that great. The sound (audio frequencies) are encoded onto the RF carrier by the transmitter then decoded from the received RF by the receiver. Once decoded, the receiver can filter out, or boost, any particular audio frequency range similarly to have an equalizer works on a stereo system.

The identifier tones are 1020 Hz ± 50 Hz or 400 Hz ± 25 Hz. The spoken male voice is typically in the 85 Hz to 180 Hz range.
 
Larry in TN said:
It's an audio frequency filter that filter in/out the frequencies that you want to/don't want to listen to. In this case, it filters our frequencies other than the frequency of the morse code tone so that the ID is more easily understood. The VOR ID is not on a separate channel or sideband.
Click to expand...
Really? I was taught that it *was* a sideband thing like @rhkennerly said, with voice on one and ID on the other, though I can't remember which was upper and which was lower.

For those wondering what the heck we're talking about: https://en.wikipedia.org/wiki/Sideband

Are there any technical references that explain this stuff better? I find VORs fascinating.
 
Larry in TN said:
People do not speak within a very narrow frequency range.
Click to expand...

I know, I know, I know! It's a hypothetical question. Hypothetical, gedankenexperiment, whatever you want to call it.

I'm just trying to understand the technology, I know my example of an FSS transmitting in the non-spoken range in a monotone voice is impossible. There is no practical situation where it would matter that's why I have to come up with a silly situation.

I think I got it now, thanks.
 
Larry in TN said:
The identifier tones are 1020 Hz ± 50 Hz or 400 Hz ± 25 Hz. The spoken male voice is typically in the 85 Hz to 180 Hz range.
Click to expand...
And in the case of VORTACs and VOR/DME the DME idents at different times and at a different pitch, so if you have both the VOR and DME on the speaker you can hear them both.
 
flyingcheesehead said:
Really? I was taught that it *was* a sideband thing like @rhkennerly said, with voice on one and ID on the other, though I can't remember which was upper and which was lower.

For those wondering what the heck we're talking about: https://en.wikipedia.org/wiki/Sideband

Are there any technical references that explain this stuff better? I find VORs fascinating.
Click to expand...
What would be the benefit of encoding a side band for the ID? That would have added unnecessary complexity and cost. The system just mixes the audio together, like a DJ talking over the intro to a song, and encodes that for transmission. The simple notch filter only requires a few electronic components and is effective.

Check the AIM to see what details it provides in the navigation section. I tried to Google the avionics text book I used in college in the 1980s but couldn't find it. There are a lot of others out there today, just make sure it includes the "old stuff" along with all the fancy new stuff.
 
Larry in TN said:
It's an audio frequency filter that filter in/out the frequencies that you want to/don't want to listen to. In this case, it filters our frequencies other than the frequency of the morse code tone so that the ID is more easily understood.
Click to expand...
Exactly as I’ve heard it described elsewhere.
 
You must log in or register to reply here.
Back
Top