AM VHF

[Mark A. Lacy]

I am a electronics engineer (RF) by trade and having worked in two-way radio for 25 + years and a extra class amateur radio operator of 25 + years I never understood why the aeronautical radio service has remained AM (amplitude modulation) as opposed to FM (frequency modulation).
I understand that AM isn't subject to Doppler effect like in FM but most aircraft operate at speeds less than mach 1, in addition AM isn't subject to the capture effect. This may or may not be a good thing during times there is a stuck microphone or heavy channel congestion.
FM equipment is less expensive, isn't subject to atmospheric noise, man made noise. and the channel bandwidth is much less in addition this would give options like C4FM digital audio.

I see many pro's to migrating to FM.
I've never observed any avionics anomalies while transmitting on FM in the cockpit in either VHF or UHF with power ratings unto 60 watts. Most of the time you wouldn't even need that much power at 8,000', 10 watts should be more than enough.
Several cool options could be integrated into an FM radio system, Automatic ID - Your FAA reg would be transmitted when the PTT is pressed along w/ GPS coordinates and perhaps a status, Including an emergency button.
Switching to FM would effectively triple - quadruple the number of aeronautical channels!
A multi mode transceiver could be produced initially to make the migration more smooth, in other words make a VHF transceiver both FM and AM selectable.
It wouldn't be extremely expensive for a migration to FM because the equipment should be less expensive to produce, a fraction of the cost of ADS-B.

 

[Capt. Geoffrey Thorpe]

So, you want me to scrap my avionics stack and start over?

Actually, you are suggesting that I add all the FM stuff in addition to what I have, and then take out the AM stuff later because it isn't going to be an instant switch on the day of install.

Then, there is what it should cost, and what avionics suppliers charge once you jump through the FAA hoops. Plus installation...

Flying isn't expensive enough already?

 

[A1Topgun]

The biggest problem I see is the upgrade cost. You say the cost is less than an AM radio, but the bottom line is I get to buy all new radios. If the FAA would lighten up on some of the certification procedures then the manufacturers would be able to make a cost effective radio. Similar to the ADS-B requirement now. The costs for ADS-B compliance came down a lot once the FAA allowed STC ADS-B installs.

 

[RyanB]

Why bother? The current system works just fine and has for decades.

 

[wsuffa]

Consider the cost. Consider that this would need to be a worldwide change. Consider the hidebound tradition The additional services you mention (especially digital) are not likely to happen without substantial cost benefit. In weak signal situations, AM is sometimes discernible where FM is not... that is particularly true if one has a variable-bandwidth receiver.

Each modulation and transmission technique has advantages and disadvantages. CW can cut through some of the noise and interference, but comes at a cost of proficiency (and non-plain-language). Sideband is a possibility, but at a cost too.

There's not really a compelling need to move to FM.

 

[DaleB]

The only barrier I see is the need for EVERYTHING to switch. There is a huge number of certified aircraft that would need very expensive upgrades/retrofits. The cost to drop a new radio in a tired old 70s era Cherokee 140 or whatever is staggering. Even if the new radio were free, a lot of owners wouldn't be able to pay for the installation. Then every airport and FBO would also need to upgrade or replace its radios and AWOS, ATIS, tower, then you have ATC, all of it.

And if you're going to get off of AM, a switch to FM wouldn't make sense. If you're going to scrap AM, then scrap analog altogether. Use that aeronautical band for a nice new shared digital mode that would eliminate the stuck mic problem altogether. Transmit the call sign with each transmission (optionally with position, course and speed), and maybe even eliminate the need for the pilot to know, care about or switch to the local frequency. Select an airport or service (Center, air-to-air, etc.) and let the radios figure it out. Of course any suck system will be designed by a politically connected committee that will be the target of a lot of private industry money, so the results will not be pretty. At all.

Switching off of AM would take years, though, as most aircraft owners and airports are dragged by the feet into the modern era.

 

[wsuffa]

And if you're going to get off of AM, a switch to FM wouldn't make sense. If you're going to scrap AM, then scrap analog altogether. Use that aeronautical band for a nice new shared digital mode that would eliminate the stuck mic problem altogether.
Switching off of AM would take years, though, as most aircraft owners and airports are dragged by the feet into the modern era.

Certain digital modes - like DMR (multi-time-slot TDMA) have distance limitations. Further, digital modes can be subject to problems from high BER, rendering voice unintelligible. Bad news in critical or emergency situations.

FM is generally OK, but subject to capture effect. An advantage to AM is that higher modulation levels can increase the average transmitted power and help in certain situations.

 

[denverpilot]

Inertia and no international requirement to narrowband.

The way off of AM is digital, not FM. It won’t happen any time soon.

 

[wsuffa]

Inertia and no international requirement to narrowband.

The way off of AM is digital, not FM. It won’t happen any time soon.

Digital protocol may be problematic at this point due to the ever-increasing intellectual property licensing costs. Not just for the transmission layer, but also for the coding/decoding layer. Then there is the standards process.... do you select something like DRM? PSK31? Another mode? There will be testing, standards meetings, involvement of ITU and RTCA, manufacturer development and testing, and deployment. Figure 10 years for standards development, then more for deployment. And enough spectrum to allow both the new standard and AM to co-exist, with potential retransmission issues so everyone can hear each other.

Of course, eliminating the pesky FLIBs would make it go easier.

 

[tawood]

Besides cost, the rationale I've always heard for keeping AM is in fact because of the capture effect. On AM, you can often hear two people at once (albeit with a harmonic squeal). Doesn't work on FM. I understand the advantages (like flying near thunderstorms, narrow channel, etc), but I don't think they are worth the upgrade.

 

[DaleB]

Certain digital modes - like DMR (multi-time-slot TDMA) have distance limitations. Further, digital modes can be subject to problems from high BER, rendering voice unintelligible. Bad news in critical or emergency situations.

FM is generally OK, but subject to capture effect. An advantage to AM is that higher modulation levels can increase the average transmitted power and help in certain situations.

Every mode has disadvantages. AM has all kinds. FM has capture that can render an entire channel useless for a considerable area. SSB has issues. Nothing is going to be perfect, but plenty could be "better", for certain definitions of better.

But it's all moot. By the time we're off of VHF AM, we'll all be worm food.

 

[denverpilot]

Digital protocol may be problematic at this point due to the ever-increasing intellectual property licensing costs.

Aww come on. You don’t want Motorola to be able to charge $3M a year per zone controller for “support” on something that is nothing more than a 1990s vintage slow assed software packet router?

LOL. Why do you hate America?!

(Second richest lawyer I know is an IP lawyer. First is a tax lawyer. We are the orchestrators of our own demise...)

 

[Velocity173]

I am a electronics engineer (RF) by trade and having worked in two-way radio for 25 + years and a extra class amateur radio operator of 25 + years I never understood why the aeronautical radio service has remained AM (amplitude modulation) as opposed to FM (frequency modulation).
I understand that AM isn't subject to Doppler effect like in FM but most aircraft operate at speeds less than mach 1, in addition AM isn't subject to the capture effect. This may or may not be a good thing during times there is a stuck microphone or heavy channel congestion.
FM equipment is less expensive, isn't subject to atmospheric noise, man made noise. and the channel bandwidth is much less in addition this would give options like C4FM digital audio.

I see many pro's to migrating to FM.
I've never observed any avionics anomalies while transmitting on FM in the cockpit in either VHF or UHF with power ratings unto 60 watts. Most of the time you wouldn't even need that much power at 8,000', 10 watts should be more than enough.
Several cool options could be integrated into an FM radio system, Automatic ID - Your FAA reg would be transmitted when the PTT is pressed along w/ GPS coordinates and perhaps a status, Including an emergency button.
Switching to FM would effectively triple - quadruple the number of aeronautical channels!
A multi mode transceiver could be produced initially to make the migration more smooth, in other words make a VHF transceiver both FM and AM selectable.
It wouldn't be extremely expensive for a migration to FM because the equipment should be less expensive to produce, a fraction of the cost of ADS-B.

Well, no VHF-FM for civil aircraft but military has been using FM (SINCGARS) in aircraft for a couple decades. Honestly never noticed much of a difference in comm quality between FM and AM VHF or UHF.

I think to retro fit all civil aircraft to FM with be cost prohibitive. Capture effect would most likely render it a no go as well.

 

[geneseib]

I am a electronics engineer (RF) by trade and having worked in two-way radio for 25 + years and a extra class amateur radio operator of 25 + years I never understood why the aeronautical radio service has remained AM (amplitude modulation) as opposed to FM (frequency modulation).

I've wondered if one reason is that with the long line of sight distances that an aircraft has, using AM does a better job of suppressing interference by far away signals. As signal weakens, modulation weakens as well.

 

[Skip Miller]

While you are at it, why not switch to the metric system? Same sort of arguments apply. What we have works, so....

 

[weilke]

Considering how smooth and easy the transition to P25 radios in the public safety sector has gone, it'll be a walk in the park to move aviation to FM and/or digital.

 

[frfly172]

Sounds good ,who’s going to cover the cost? Aircraft ownership ,isn’t getting any cheaper.

 

[idahoflier]

I agree, AM sucks! But as others have said there is the cost involved that makes me want to continue to live with it...

 

[wsuffa]

Considering how smooth and easy the transition to P25 radios in the public safety sector has gone, it'll be a walk in the park to move aviation to FM and/or digital.

Wait for FirstNet.

 

[coloradobluesky]

Now switching to the metric system would be a good idea. The USA is about the only country not on it.

 

[weilke]

Wait for FirstNet.

It's AT&T, it'll be perfect right out of the gates.

 

[airdale]

Even though I was trained as an engineer, I sill find it quite funny to see an engineer bewildered when he runs smack dab into the real world. Mr. Lacy, you are sub-optimizing. As in most cases, a large installed base of equipment trumps whatever small improvements an alternative technical solution might offer. Even revolutionary improvements are difficult to sell.

You really have to look no farther than Great Britain and its former colonies (+Japan) that drive on the left. Would they rather conform to the world standard of driving on the right and thus be able to use standard cars? Of course, but the cost and difficulty of converting the installed base trumps the advantages. I was recently in Myanmar, where one of the generals has decreed that cars will drive on the right. Unfortunately almost all of the cars there are right-hand drive. Traffic in Yangon is quite crazy as a result and people riding "shotgun" now have a role as oncoming traffic spotters during passing.

 

[Clip4]

I am a electronics engineer (RF) by trade and having worked in two-way radio for 25 + years and a extra class amateur radio operator of 25 + years I never understood why the aeronautical radio service has remained AM (amplitude modulation) as opposed to FM (frequency modulation).
I understand that AM isn't subject to Doppler effect like in FM but most aircraft operate at speeds less than mach 1, in addition AM isn't subject to the capture effect. This may or may not be a good thing during times there is a stuck microphone or heavy channel congestion.
FM equipment is less expensive, isn't subject to atmospheric noise, man made noise. and the channel bandwidth is much less in addition this would give options like C4FM digital audio.

I see many pro's to migrating to FM.
I've never observed any avionics anomalies while transmitting on FM in the cockpit in either VHF or UHF with power ratings unto 60 watts. Most of the time you wouldn't even need that much power at 8,000', 10 watts should be more than enough.
Several cool options could be integrated into an FM radio system, Automatic ID - Your FAA reg would be transmitted when the PTT is pressed along w/ GPS coordinates and perhaps a status, Including an emergency button.
Switching to FM would effectively triple - quadruple the number of aeronautical channels!
A multi mode transceiver could be produced initially to make the migration more smooth, in other words make a VHF transceiver both FM and AM selectable.
It wouldn't be extremely expensive for a migration to FM because the equipment should be less expensive to produce, a fraction of the cost of ADS-B.

Not only would you require upgrading all the aircraft and ground stations, the FCC would have to reallocate FM frequencies from current users and reallocate the AM frequencies vacated by aviation, which would cost billions in hardware change.

Then you got to convince the remainder of the planet to change.

 

[wsuffa]

Not only would you require upgrading all the aircraft and ground stations, the FCC would have to reallocate FM frequencies from current users and reallocate the AM frequencies vacated by aviation, which would cost billions in hardware change.

Then you got to convince the remainder of the planet to change.

Naw, they would leave the frequencies the same and just change the allowable emissions. That would be easy if it weren't for needing to change the worldwide allowable emissions table. You can use most types of modulation on any frequency, subject to bandwidth limits.

 

[weilke]

If anything happens it will be a move to digital in higher frequency bands. It'll cost bazillions of dollars and provide only marginal improvements in communication.

But then, with NextGen 2.0 there won't be any need for voice communications. It's all ballbearings and plastics!

 

[Mark A. Lacy]

AM to FM - It was just a suggestion to provoke some intelligent feedback, not sarcasm.
I agree the FAA does need to lighten up on its certification policy.
As for the metric system, I don’t like the metric system, most Americans don’t want anything to do with it.
Furthermore, the metric system has absolutely nothing to do with the forum post.
It’s about AM to FM. It was just a “what if” idea. I realize it will most likely never happen.
As far as the digital comment about DMR, (TDMA) would be a bad choice for the aviation radio service.
As for ADS-B I haven’t heard too many pilots belly ache about the mandate, I believe it’s money well spent. ADS-B will save lives.
Enough said.

 

[wsuffa]

Aww come on. You don’t want Motorola to be able to charge $3M a year per zone controller for “support” on something that is nothing more than a 1990s vintage slow assed software packet router?

LOL. Why do you hate America?!

(Second richest lawyer I know is an IP lawyer. First is a tax lawyer. We are the orchestrators of our own demise...)

And then there are SAP salespeople that put both to shame...

 

[AU_James]

Why bother? The current system works just fine and has for decades.

... said the FAA about everything, ever.

But to the OP's question, the conversion from what we have now to what we could have just isn't worth the associated costs to aircraft owners. We're already doing ADS-B (and many are kicking and screaming the whole way). If it's just a quality of life thing and not necessarily delivering a level of safety some other upgrade, I don't see it getting support.

If the FAA becomes privatized, however, draft up your proposal!!

 

[denverpilot]

And then there are SAP salespeople that put both to shame...

A good SAP admin/developer was making $150K a year in the early 2000s. Assuming inflation, it’s a $200K a year job by now.

Know someone who made that consulting just to tell a company over a seven year timeframe that their SAP design litterally wasn’t written in such a way that they could handle the purchase they made of a new business for Wall Street growth.

Estimates when that person finally retired and said they were done, were over $100M to re-rewrite the SAP system to handle selling finished product, something that company had never done until they bought the sub-company.

Wasn’t included in the due diligence paperwork nor accounted for as a cost incurred as part of the acquisition. Of course.

 

[wsuffa]

A good SAP admin/developer was making $150K a year in the early 2000s. Assuming inflation, it’s a $200K a year job by now.

Know someone who made that consulting just to tell a company over a seven year timeframe that their SAP design litterally wasn’t written in such a way that they could handle the purchase they made of a new business for Wall Street growth.

Estimates when that person finally retired and said they were done, were over $100M to re-rewrite the SAP system to handle selling finished product, something that company had never done until they bought the sub-company.

Wasn’t included in the due diligence paperwork nor accounted for as a cost incurred as part of the acquisition. Of course.

Of course.

True story: a Fortune 600 company using SAP acquired a company in the UK. At 3 years and $8 million, they hadn't finished the SAP conversion.

At least one salesperson for SAP was known to drive a Maserati. That's well above $300K territory.