AM or FM, Question, Please

[BOBRR]

Hello,

For aero. freq's like, e.g.:

Aero Gander CG 12: Sector 15 Surry on 346,000.000 which I'm assuming is 346+ MHz (true ?)

Is this fm or am ?

Are all aero. frequencies above 30 MHz "always" fm ?
Or,...?

And, what is "CG" ? It's not a Coast Guard freq., or is it ?

Thanks,
Bob

 

[jonsmth]

Are all aero. frequencies above 30 MHz "always" fm ?
Or,...?

In the 23 years I operated in Naval Communications, the majority of our Communications with Aircraft
were in "AM". There were a few times when we worked with NATO countries that they used "FM", but most
of the time we communicated in "AM." The UHF transceivers we used could operate in either AM or FM.

 

[andy51edge]

Aero Gander CG 12: Sector 15 Surry on 346,000.000 which I'm assuming is 346+ MHz (true ?)

Correct, 346 MHz.

Is this fm or am ?

Are all aero. frequencies above 30 MHz "always" fm ?
Or,...?

Let me add the "in general" disclaimer and say that most VHF (above 30MHz) and UHF aircraft voice communications are done in AM.

And, what is "CG" ? It's not a Coast Guard freq., or is it ?

I would assume so but more context would help make this more certain.

 

[ATCTech]

What is the source document of the reference to 346? I suspect CG may be Coast Guard, although they do not provide air traffic control services. I'm looking at the Gander Centre frequencies from an edition of the Canada Flight Supplement in 2021 and there is no remote site location in a location of "Surry" nor is 346.0 listed at any Gander Centre remote radio location. The CFS is "the" official NAV Canada document for our facilities, published every 56 days, as are many ICAO documents. An ATC sector name and number used internally would not normally appear in our documentation for public use.

Also FWIW, all of our ATC radios (VHF and UHF) are AM.

Cheers!

 

[spanky15805]

ATCTech. Would this be the same Gander I hear on 10.051 usb?

 

[ATCTech]

I'm still not at all sure what the "CG" and 346.0 MHz frequency is but in the case of actual ATC communications, the same Gander location yes, but the HF radio work is done by Gander IFSS ("Gander Radio" on the air). ATC "controls" the aircraft over our oceanic airspace (out to 30W) but the IFSS (International Flight Service Station) at Gander handles the HF (and some long-range and remote) VHF voice traffic on their behalf, much like ARINC does the HF comms for the FAA ATC system except that here in Canada we're all part of NAV Canada, not two different organizations. I believe the VOLMET is also an FSS (vs. ATC) responsibility. The Gander Area Control Centre (ACC to us, ARTCC to the FAA) facility handles all of the domestic airspace ATC communications directly.

 

[K2QWQ1]

Hello,

For aero. freq's like, e.g.:

Aero Gander CG 12: Sector 15 Surry on 346,000.000 which I'm assuming is 346+ MHz (true ?)

Is this fm or am ?

Are all aero. frequencies above 30 MHz "always" fm ?
Or,...?

And, what is "CG" ? It's not a Coast Guard freq., or is it ?

Thanks,
Bob

When radio was first installed in aircraft, 1930s +-, AM was all there was so all aircraft ended up using AM. Since airport and ATC comms are usually short distances and line of sight, there is no need for especially sensitive or high powered gear. Indeed, receiver in the planes are 'deaf' by amateur radio standards - a plane at 30,000 ft would be swamped by signals from hundreds of miles away if the rx were very sensitive.

Even military use AM for most air comms with a few exceptions - Navy, Coast Guard, S&R, other aircraft involved in comms on the ocean may have FM capability in order to speak to those aboard with only FM rigs.

73, DE K2QWQ Doug

 

[BC_Scan]

there is no remote site location in a location of "Surry"

Sorry to jump in but in the West Coast of Canada there is a remote site @ Surrey British Columbia , not sure of your context, run by Nav Canada

 

[littona]

Learning time... Who can answer why are most ATC comms still in AM?

 

[xms3200]

It will be very expensive to switch to FM worldwide

 

[W0JOG]

The allocations for frequencies and modulation are by International agreement as is the accepted phonetics for each letter (Alpha for "A", etc.). That is to avoid as much error as possible. The international aviation organization is ICAO.

de W0JOG

 

[nd5y]

AM is about 6 kHz wide. Narrow FM is about 11 KHz wide. There is a move to 8.33 kHz channel spacing in the AM aircraft band. It's already used in Europe. You can't do that with FM.

 

[ATCTech]

Sorry to jump in but in the West Coast of Canada there is a remote site @ Surrey British Columbia , not sure of your context, run by Nav Canada

Yup, and a l-o-n-g way from CYQX territory!

 

[bearcatrp]

Correct me if I am wrong but isn't 380 to 400 Mhz NFM? Was on a ride last weekend and took my R30. Picked up a signal in the 380 ish area on am. Couldn't understand them until I changed mode to NFM. Was able to listen in then.

 

[andy51edge]

Correct me if I am wrong but isn't 380 to 400 Mhz NFM? Was on a ride last weekend and took my R30. Picked up a signal in the 380 ish area on am. Couldn't understand them until I changed mode to NFM. Was able to listen in then.

There is land mobile (FM) and trunked radio stuff in that band. However aircraft still use that slice of the band, and when they do it's normally AM.
So be flexible above 380.

 

[samka4att]

Learning time... Who can answer why are most ATC comms still in AM?

FM has a capture effect..... if a plane captures the frequency and is stronger, another one will not be able to be heard. That doesn't happen in AM.... the signal may have a chance to be heard.

 

[ATCTech]

EXACTLY right @samka4att!! That's just how it was explained to me in the ealiest days of my career in ATC electronics. Thank you for such a succinct response.

 

[u2brent]

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.718.6641&rep=rep1&type=pdf

 

[ATCTech]

For the record, here are photos of the actual UHF air band radios we have used in ATC in Canada since the late 1970s. They were also available in VHF models, although in Canada we did not use the AM variant. The ITT GRT-22 exciter (10W nominal) and the GRR-24 receiver. There was also a 100W RF amplifier available. (Photos "borrowed" from online sources, these ones have seen better days!)

 

[ATCTech]

Good work @u2brent!