Why don't voice radio communications use FM?

Emily schrieb:

There were many other steps in the accident
chain, but Tenerife was most certainly not caused by a pilot hearing
what he wanted to hear.

Actually, the KLM captain hearing what he wanted to hear was most
certainly the main cause for that accident.

As a consequence of this misunderstanding, the word "take-off" shall now
only be used in "cleared for take off" and in the read-back of this
clearance, or, at uncontrolled airfields, when a pilot says that he is
taking off. No more "ready for take off", "stand by for take off" and
the like, and no taking off before you are absolutely positively sure
that you have heard and read back the word.

But all this had nothing to do with the readability of the radio
transmissions.

Stefan

Stefan wrote:
Emily schrieb:

There were many other steps in the accident chain, but Tenerife was
most certainly not caused by a pilot hearing what he wanted to hear.

Actually, the KLM captain hearing what he wanted to hear was most
certainly the main cause for that accident.

As a consequence of this misunderstanding, the word "take-off" shall now
only be used in "cleared for take off" and in the read-back of this
clearance, or, at uncontrolled airfields, when a pilot says that he is
taking off. No more "ready for take off", "stand by for take off" and
the like, and no taking off before you are absolutely positively sure
that you have heard and read back the word.

But all this had nothing to do with the readability of the radio
transmissions.

Stefan
That was my point. He heard what he wanted to hear, but not because of
jarbled radio transmission.

Mxsmanic wrote:

Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio?

I understand it is because of a characteristic of FM called "capture
effect" that blanks out weaker transmissions when two radios transmit at
the same time. The listener would have no idea that a second, weaker
transmission was being made.

With AM, when two radios transmit on close frequencies, you either hear
both signals poorly, or you get squeal, which is the sum of the two
signals. This characteristic is considered important when you have elevated
transmitters that can be hundreds of miles away, like on aircraft.

Red herring, again. AM radio does the same suppression effect if the
signals are widely differing in power (google "AGC" or "AVC" for an
explanation). The odds of two signals being absolutely equal in time is
close to zero. True, they can start simultaneously, but the ending time is
generally measured in multiseconds. One side or the other always gets the
tag end of one conversation or the other and can figure out that a second
station is trying to get a message across.

The squeal when two nearly equal power signals is not the sum of the
frequencies, it is the difference.


Jim



"James Robinson" wrote in message
. ..
Mxsmanic wrote:

Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio?

I understand it is because of a characteristic of FM called "capture
effect" that blanks out weaker transmissions when two radios transmit at
the same time. The listener would have no idea that a second, weaker
transmission was being made.

With AM, when two radios transmit on close frequencies, you either hear
both signals poorly, or you get squeal, which is the sum of the two
signals. This characteristic is considered important when you have
elevated
transmitters that can be hundreds of miles away, like on aircraft.

"James Robinson" wrote in message

With AM, when two radios transmit on close frequencies, you either hear
both signals poorly, or you get squeal, which is the sum of the two
signals. This characteristic is considered important when you have
elevated
transmitters that can be hundreds of miles away, like on aircraft.

Sounds plausible. Marine radios also operate in the VHF band, but are FM.
They are also almost always at or very close to sea level.

James Robinson wrote:
Mxsmanic wrote:

Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio?

I understand it is because of a characteristic of FM called "capture
effect" that blanks out weaker transmissions when two radios transmit at
the same time. The listener would have no idea that a second, weaker
transmission was being made.

No actually, it's just historical. Early av radio used AM, and for that
reason we still do.

"Ron Natalie" wrote in message
m...

No actually, it's just historical. Early av radio used AM, and for that
reason we still do.


Didn't all early radio use AM?

On Sat, 02 Sep 2006 16:58:12 GMT, "Steven P. McNicoll"
wrote in
. net:


"Ron Natalie" wrote in message
om...

No actually, it's just historical. Early av radio used AM, and for that
reason we still do.


Didn't all early radio use AM?


Early radio, including aviation, used Continuous Wave (CW) modulation
and Morris Code.

Edwin Armstrong patented Frequency Modulation (FM) in 1933.*


* http://en.wikipedia.org/wiki/Edwin_Howard_Armstrong

"Steven P. McNicoll" wrote in message
ink.net...

"Ron Natalie" wrote in message
m...

No actually, it's just historical. Early av radio used AM, and for that
reason we still do.


Didn't all early radio use AM?

Nope, it was quite a ways down the line. Morse code via spark gap
transmitters was one of the first.

Dave Stadt writes:

Nope, it was quite a ways down the line. Morse code via spark gap
transmitters was one of the first.

All early audio used AM.

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