COM vs NAV & LOC vs VOR

mandm

mandm

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Trying to better understand the equipment in an airplane. I think its pretty straight-forward to understand a single piece of equipment, but more difficult to understand how they work together.

COM vs NAV
Is there a difference in COM vs NAV? I know that one is probably for COM radio and one is for NAV, but are they the same radio technology? Could you use a COM radio with a VOR / LOC with a CDI? Or are they two completely different technologies?

LOC vs VOR
What is the difference between LOC and VOR? Could these essentially both work with a COM or NAV radio and CDI?
 
mandm said:
Is there a difference in COM vs NAV? I know that one is probably for COM radio and one is for NAV, but are they the same radio technology? Could you use a COM radio with a VOR / LOC with a CDI? Or are they two completely different technologies?
Click to expand...
NAV radio is 108Mhz-117Mhz. COM radio is 118Mhz-136Mhz. How do you plan to get the COM radio to tune NAV frequencies?
 
COM and NAV are both VHF radios, but on different frequency ranges. A COM radio can't receive the NAV frequencies and vice versa. A COM radio is for talking and can transmit, has a microphone input, whereas a NAV radio can receive voice (station identifier or remote communications) but can't transmit and has the additional circuitry necessary to drive the CDI, for VOR or LOC. LOC is like VOR, but with a narrow range for an approach, instead of 360° for the VOR.

When you have a NAV/COM in one box they may share some components like the audio amplifier but the functionality for each side is the same as discrete units.
 
Dana said:
COM and NAV are both VHF radios, but on different frequency ranges. A COM radio can't receive the NAV frequencies and vice versa. A COM radio is for talking and can transmit, has a microphone input, whereas a NAV radio can receive voice (station identifier or remote communications) but can't transmit and has the additional circuitry necessary to drive the CDI, for VOR or LOC. LOC is like VOR, but with a narrow range for an approach, instead of 360° for the VOR.

When you have a NAV/COM in one box they may share some components like the audio amplifier but the functionality for each side is the same as discrete units.
Click to expand...

Thank you for the explanation! So any CDI + NAV would be able to pick up either LOC or VOR with just the range difference for an approach?
 
mandm said:
Thank you for the explanation! So any CDI + NAV would be able to pick up either LOC or VOR with just the range difference for an approach?
Click to expand...

In principle, you could "listen" to a NAV radio if you have a speaker hooked up. You will hear a 9.9kHz audio signal and the Morse code. It won't mean anything unless you have the proper demodulation hardware (which the NAV receiver does).
 
Dana said:
COM and NAV are both VHF radios, but on different frequency ranges. A COM radio can't receive the NAV frequencies and vice versa. A COM radio is for talking and can transmit, has a microphone input, whereas a NAV radio can receive voice (station identifier or remote communications) but can't transmit and has the additional circuitry necessary to drive the CDI, for VOR or LOC. LOC is like VOR, but with a narrow range for an approach, instead of 360° for the VOR.

When you have a NAV/COM in one box they may share some components like the audio amplifier but the functionality for each side is the same as discrete units.
Click to expand...

‘however, you can communicate duplex, with FSSs in particular, listening on a NAV vor freq but transmitting on a comm frequency. It’s all, quite complex sometimes.
 
And vor gives horizontal (geographic) guidance to or from a vor station. Loc (localizer) gives vertical guidance up & down to a runway. Combined together they make-up an ILS (looks like cross of vertical & horizontal needles) you kept centered & they will guide you down to the runway during an instrument approach.


Oh, and a bit of an oddity, a throwback to the earliest days of flying) aviation comm radios are Amplitude modulation (like AM radio), not FM.
 
rhkennerly said:
And vor gives horizontal (geographic) guidance to or from a vor station. Loc (localizer) gives vertical guidance up & down to a runway. Combined together they make-up an ILS (looks like cross of vertical & horizontal needles) you kept centered & they will guide you down to the runway during an instrument approach.


Oh, and a bit of an oddity, a throwback to the earliest days of flying) aviation comm radios are Amplitude modulation (like AM radio), not FM.
Click to expand...
Almost. A localizer will give you horizontal guidance, on the same CDI as selecting a VOR frequency, except you don't need to dial the heading into the CDI (it does help logically to do so anyway but it's not required).
To get vertical guidance your NAV radio needs a glideslope receiver which will either be another box behind your panel or an extra circuit board in your NAV radio.
 
mandm said:
Thank you for the explanation! So any CDI + NAV would be able to pick up either LOC or VOR with just the range difference for an approach?
Click to expand...

The CDI, HSI, ILS, VOR are all different kinds of displays that CAN be driven by a Nav Radio output. CDIs & HSIs can also be driven by GPS. CDI & HSIs are hybrid instrument heads that combine any number of functions into one head. You could run either in reduced capacity displaying other functions without a nav or gps radio, but they’re crippled.
 
aftCG said:
Almost. A localizer will give you horizontal guidance, on the same CDI as selecting a VOR frequency, except you don't need to dial the heading into the CDI (it does help logically to do so anyway but it's not required).
To get vertical guidance your NAV radio needs a glideslope receiver which will either be another box behind your panel or an extra circuit board in your NAV radio.
Click to expand...

Understood. Trying to keep it simple.
 
Oh, and don’t forget marker beacons, adf, & dme or cranking out a spool of wire for HF…;->

tomorrow’s lesson, inertia tables.
 
mandm said:
Thank you for the explanation! So any CDI + NAV would be able to pick up either LOC or VOR with just the range difference for an approach?
Click to expand...

Not range (though I wouldn't be surprised if localizer transmitters have lower power than VORs, I don't know), it's the width of the area served and as aftCG said you don't have to dial it in on the OBS. But yes, you pick up the localizer with a VOR receiver, and if it also have a glideslope receiver, the horizontal glideslope needle is added to the CDI for vertical guidance.

rhkennerly said:
‘however, you can communicate duplex, with FSSs in particular, listening on a NAV vor freq but transmitting on a comm frequency. It’s all, quite complex sometimes.
Click to expand...
That's what I meant by "remote communications."
 
As for LOC vs VOR, the each frequency is designated as being either for VOR or LOC. If there is a GS, it's up in the UHF band but on frequencies paired to the VHF localizer ones. VOR uses two signals one of which phase varies based on the direction. Both LOC and VOR use two directional signals that the relative intensities tell you where you are with regard to the center.
 
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rhkennerly said:
Oh, and a bit of an oddity, a throwback to the earliest days of flying) aviation comm radios are Amplitude modulation (like AM radio), not FM.
Click to expand...

I noticed that recently when trying to program the local tower frequency into a cheapie Baofeng radio, just to listen to ATC. I have a much nicer radio at home that will do AM, SSB, etc., but it definitely won't fit into my pocket :D
 
mandm said:
Trying to better understand the equipment in an airplane. I think its pretty straight-forward to understand a single piece of equipment, but more difficult to understand how they work together.

COM vs NAV
Is there a difference in COM vs NAV? I know that one is probably for COM radio and one is for NAV, but are they the same radio technology? Could you use a COM radio with a VOR / LOC with a CDI? Or are they two completely different technologies?

LOC vs VOR
What is the difference between LOC and VOR? Could these essentially both work with a COM or NAV radio and CDI?
Click to expand...

COM is for two-way voice communications (with ATC). NAV is for area navigation, receive only. Totally different functions, but yes, they use the same technology: AM radio on the VHF band. VOR and LOC are the ground transmitters. The CDI is the instrument in the plane that tells you your position relative to the ground station. Manufacturers used to combine these two radios into one box because they could share some hardware. Called a NavCom. Nowadays, GPS receivers have little in common with a COM radio, so they are often separate boxes.

VORs can be used from any direction (usually) - 360 degrees. You select a radial on the CDI and it will tell you your position relative to that radial. LOC (localizer) is the same technology, but is used specifically for an approach to an airport. It also uses the CDI in the same way, but you don't select a radial. The final approach course is pre-set. LOC provides horizontal guidance (left-right) only. But it can be combined with a 'glideslope' (GS) receiver to provide vertical guidance also. When you have LOC and GS combined with appropriate approach lights and runway markings, you have an Instrument Landing System (ILS).

C.
 
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