AIRPLANE FREQS.

[ShawnCowden]

WHY IS THE AIRPLANE FREQS. RANGE IN AM MODE ???

 

[loumaag]

The short answer is, because they always were. Actually VHF used to be almost all in AM mode a while back. However, since FM proves to be able to provide a cleaner signal in adverse conditions the Land Mobile services started using FM as opposed to AM. Since each agency made that decision on its own, it was not a huge impact at any one time. However, if the FAA suddenly decided to switch to FM from AM, consider the economic impact of that. Hence, it has been AM ever since. BTW, for it's applicability for "line of sight" communication such as air-to-air and air-to-ground, AM works quite well at VHF.

 

[ShawnCowden]

i though so I didnt know if am traveled farther then fm or not. I know ssb does.
Its neat hearing airplanes in ssb hf mode and local airplanes. thanks for the info.

 

[AZScanner]

The short answer is, because they always were. Actually VHF used to be almost all in AM mode a while back. However, since FM proves to be able to provide a cleaner signal in adverse conditions the Land Mobile services started using FM as opposed to AM. Since each agency made that decision on its own, it was not a huge impact at any one time. However, if the FAA suddenly decided to switch to FM from AM, consider the economic impact of that. Hence, it has been AM ever since. BTW, for it's applicability for "line of sight" communication such as air-to-air and air-to-ground, AM works quite well at VHF.

I remember speaking with a private pilot/retired FAA controller a few years ago who told me that cost has nothing to do with not switching to FM. The reason AM was and is still used is because unlike FM, two people can talk at once and still be heard. Don't know how true that was, but considering the man's qualifications, I tend to believe him.

FWIW.

-AZ

 

[mlevin]

Yes I believe that's true, but don't think that was the reason for no switching to AM. Logistcally it's a nightmare. And yes it most likely would cost alot of money. Add the fact that little would be gained from switiching and there you go. Everyone is staying put.

 

[N_Jay]

Yes I believe that's true, but don't think that was the reason for no switching to AM. Logistcally it's a nightmare. And yes it most likely would cost alot of money. Add the fact that little would be gained from switiching and there you go. Everyone is staying put.

Except for the move to digital coming soon.

 

[mlevin]

What kind of digital are they planning on moving to? Also, why digital, it's a whole lot more expensive then FM

 

[N_Jay]

What kind of digital are they planning on moving to? Also, why digital, it's a whole lot more expensive then FM

I think we had this discussion already.

Look up NEXCOM

http://www.copanational.org/non-members/Newsletter/newsMarch04G.htm

http://www.flyingmag.com/article.asp?article_id=357&print_page=y

http://www.aviationtoday.com/cgi/av/show_mag.cgi?pub=av&mon=1203&file=1203nexcom.htm

http://www.pilotfriend.com/pilot_resources/other resoources/Next Generation Avionics.htm

http://www.house.gov/transportation/aviation/10-31-03/10-31-03memo.html

 

[fireant]

I work very closely with the Faa and talk to alot of people digital will be at least nine to ten years down the road. The Faa and the Military are still training people on these system with no plans to switch anytime soon. I talked to the director of the Faa academy friend of mine he said don't look for digital for aircraft any time soon or in the near future.


fireant

 

[Voyager]

The short answer is, because they always were. Actually VHF used to be almost all in AM mode a while back. However, since FM proves to be able to provide a cleaner signal in adverse conditions the Land Mobile services started using FM as opposed to AM. Since each agency made that decision on its own, it was not a huge impact at any one time. However, if the FAA suddenly decided to switch to FM from AM, consider the economic impact of that. Hence, it has been AM ever since. BTW, for it's applicability for "line of sight" communication such as air-to-air and air-to-ground, AM works quite well at VHF.

I remember speaking with a private pilot/retired FAA controller a few years ago who told me that cost has nothing to do with not switching to FM. The reason AM was and is still used is because unlike FM, two people can talk at once and still be heard. Don't know how true that was, but considering the man's qualifications, I tend to believe him.

That's exactly the reason they are still using AM. You can't jam someone (intentionally or unintentionally) using AM with another AM transmitter. Both transmissions will still be heard, unlike FM where only the strongest transmission is heard due to capture effect. I believe this same question was brought up in other threads.

If someone has an emergency, they don't have to wait for anyone else to stop talking before they can declare it. They can instantly key up and let everyone know their status. Think of it as talking in a group of people - even if someone else is talking, you can say "FIRE!" and everyone will still hear you. If everyone 'talked in FM', people would only hear the strongest transmission (typically the one closest).

Joe M.

 

[ShawnCowden]

will we be able to monitor the new digital aviation channels ??

sounds like if not then we will never be able to listen to anything our hobby will be gone for good

 

[mlevin]

You can always buy an aviation radio. Todays HTs are only a few hundred dollars. Although the price will most likely go up once the switch to digital occurs. However I'm sure a hobbyist could still get there hands onone. Either that or someone will make a scanner able to monitor these comms.

 

[Waldo325mvfd]

why digital?

8)

 

[mlevin]

Click on the first link posted above for a really good explanation.

 

[mstarn]

The FAA will probably go to digital in about 2015. That is if Congress gives the 3 Billion dollars plus (Yes! I said billion) to change to digital. That cost does not include the airlines, and General Aircraft guys, and military. Today the FAA has somewhere about 40,000 plus radios of different types in their inventory. The FAA has VHF/FM, VHF/AM, HF, UHF and sat comm radios today. They must be able to talk to any aircraft, anywhere. Not with just radio but two, one is for back up in case the main radio fails. One of the main problems today is the old, old system needs upgrading - grounds, antenna towers, power, etc. to enable a new systems to be used to it's fullest. This is besides the never ending money problem. They have to maintain the old system while installing and "cutting over" to the new system. That is analog to digital. Just cannot throw the switch one night at nidnight and make it happen. Airlines, control tower, and en route centers must stage a cut over over a period of time. Sorry I'm so long winded - this is kind of near and dear to my heart.

 

[loumaag]

I remember speaking with a private pilot/retired FAA controller a few years ago who told me that cost has nothing to do with not switching to FM. The reason AM was and is still used is because unlike FM, two people can talk at once and still be heard. Don't know how true that was, but considering the man's qualifications, I tend to believe him.

Well that is certainly true, AM does not have the "capture" effect like FM; however, both stations need to be relatively far away from the receipient for that effect to really have an impact on communicationis. You can find out just how sucessful that is by tuning into any CB channel. :lol:

 

[N_Jay]

I remember speaking with a private pilot/retired FAA controller a few years ago who told me that cost has nothing to do with not switching to FM. The reason AM was and is still used is because unlike FM, two people can talk at once and still be heard. Don't know how true that was, but considering the man's qualifications, I tend to believe him.

Well that is certainly true, AM does not have the "capture" effect like FM; however, both stations need to be relatively far away from the receipient for that effect to really have an impact on communicationis. You can find out just how sucessful that is by tuning into any CB channel. :lol:

Personally I think the "AM Excuse" is more of a "justification after the fact" than any reason that had been part of a decision process! :wink:

 

[INDY72]

Facts: A- It WILL be a worldwide Logistics NIGHTMARE for the world to change from what it is using now,.. this is not just a USA thing here, this is a WORLDWIDE thing here.
B- It WILL be a worldwide Financial NIGHTMARE when this all starts happening,.. being that just the finacial status of the USA ALONE sucks,.. look at the rest of the world.
C- This HAS to be done by every aircraft, monitoring station, airport, military aviation agency in the world, as stated not just the USA,.. All aviation MUST be able to interop and communicate effectively WORLDWIDE!

Consider the ramifications of GLOBAL changeover in aviation in ANY form.... Why do you think English is the standard civilian avaition language WORLDWIDE????? So everyone is able to communicate with one standard! Military aviation is very different! When the Land Mobile was able to get easy to use, smaller, less cumbersome FM for radio usage,.. the entire WORLD had already been using AM for aviation for a very long time as compared to FM. Changing to FM would be even harder and more costly than just digitizing the AM format.

All this hoopla about FAA this, and FAA that,.. you forget all about the rest of the world guys.. thats like all we ever mention is FCC this, FCC that,.. the FAA, and FCC have got nada, zip, zilch, ZERO to do with what the rest of the world has to do. So just think about that one.