The third number

[UnAnswerd]

One particular approach control frequency is listed as 120.925. Ground gives it out as 120.92, and that number works fine in the radio. Is this typical, a third number after the decimal doesn't hold much meaning???

 

[FL000]

The third number is always a 0 or a 5, and can be assumed by what precedes it (which will be a 0, 2, 5, or 7):

0 > 0
2 > 5
5 > 0
7 > 5

See a pattern? Each first digit after the decimal is quartered.

 

[User546]

I was wondering along this same lines the other day while flying.

Why do they still publish the third number with some frequencies. Any aircraft I've ever flown in (old and new) have only made it possible to enter two digits. Why bother putting the third number on there, all it does it give you an extra number to have to glance at, and for all I can tell, serves no purpose.

I'm sure there is probably a good, logical answer out there of why, but I'm going to need someone else's knowledge to discover it.

 

[ISaidRightTurns]

FL000 is correct, frequencies are quatered starting at the 2nd digit after the decimal place.

I think most radios automatically adjust, or it might be close enough in frequency that it doesn't matter. I think they adjust.

 

[DaveJ]

The radio actual tunes to 132.025 it just doesn't show the last digit. My handheld has a similiar issue. To tune in 132.025, I punch in 32025 ENTER. The intial 1 for the hundreds of MegaHertz and the decimal point aren't needed.

 

[FN FAL]

I was wondering along this same lines the other day while flying.

Why do they still publish the third number with some frequencies. Any aircraft I've ever flown in (old and new) have only made it possible to enter two digits. Why bother putting the third number on there, all it does it give you an extra number to have to glance at, and for all I can tell, serves no purpose.

I'm sure there is probably a good, logical answer out there of why, but I'm going to need someone else's knowledge to discover it.

Think of it this way, It's not that they are publishing the third number...it's that they are not publishing the 4th, 5th and 6th number...

Would you want to read this on your charts or get this every time you were told to change freq's by a controller...

"November Five Six Seven Lima Tango ...change to my frequency, One Hundred Twenty Five Million, Seven Hundred and Twenty Five Thousand...."

"Rodger, One Twenty Five Point Seven Two!"

 

[User546]

Think of it this way, It's not that they are publishing the third number...it's that they are not publishing the 4th, 5th and 6th number...

Would you want to read this on your charts or get this every time you were told to change freq's by a controller...

"November Five Six Seven Lima Tango ...change to my frequency, One Hundred Twenty Five Million, Seven Hundred and Twenty Five Thousand...."

"Rodger, One Twenty Five Point Seven Two!"

Exactly my point FN FAL, but to a lesser extent.

With what you said in mind, why even add in the THIRD number, the same way you don't add in the 4th, 5th, 6th, etc.

You can only enter two digits, why bother with, or publishing, a third number?

 

[Stepclimb]

More channels are coming

Maybe it has something to do with European and other foreign airlines flying in the states.
Current US comm. radios operate in AM and have 760 frequencies (25 kHz spacing between 118.00-136.975 MHz).

In Europe and other countries, the radio spectrum is saturated and they have turned to 8.33 kHz spacing to make more possible 'channels' within the existing spectrum.
To alleviate confusion, US plates take the freq out to 3 decimal places for exact tuning on 8.33 kHz radios.
I think there is a push in this country to move towards 8.33 kHz spacing. Remember not too long ago, when we made the change from 50 kHz (360 channel) spacing to to 760 channels? The FAA & FCC mandated .003 kHz stability and essentially outlawed the older radios. It's just a matter of time before we see 8.33 radios in the states.....

-Stepclimb

 

[FL000]

I think you mean that we operate FM frequencies. AM is the ADF.

Also, I was wondering why someone in a white lab coat hasn't come up with a non-jamming comm system, like sat-com. It would work more or less like a telephone where you can hear the other person even if you are also talking. Just think, no more "BLOCKED" calls.

 

[Stepclimb]

AM vs FM

Negative....
Aircraft Communication radios operate with Amplitude Modulation. Ever hear the crackle of static when operating near electrical storms?
The only FM comm. radios with which I'm familiar are in use with the Army. Some Army aircraft have these 'Fox Mike' radios to communicate with ground forces.

 

[FL000]

I thought that the freqs started just above the commercial frequencies on the FM band...108.00 >>>

Those are AM? I'll admit I know near nothing about communication technologies, but that just seemed practical to me.

 

[UnAnswerd]

I thought that the freqs started just above the commercial frequencies on the FM band...108.00 >>>

Those are AM? I'll admit I know near nothing about communication technologies, but that just seemed practical to me.

I thought that too. I mean, FM radio is VHF, as is the aviation frequency range, no? Of course, I too know nothing about the mechanics of radio waves...

 

[Daveman]

I thought that too. I mean, FM radio is VHF, as is the aviation frequency range, no? Of course, I too know nothing about the mechanics of radio waves...

What's the "deal" after you toss my salad! You don't fool me.

 

[FN FAL]

I think you mean that we operate FM frequencies. AM is the ADF.

Also, I was wondering why someone in a white lab coat hasn't come up with a non-jamming comm system, like sat-com. It would work more or less like a telephone where you can hear the other person even if you are also talking. Just think, no more "BLOCKED" calls.

You'd think in this day and age, that you'd get a "ding" look at a screen and see..."descend and maintain 4,000 feet." Then you'd push a "Rodger-Wilco" button and then push a button sending it to the FMS.

Then, if you had a request, you'd hit some hot button keys and send it to ATC...then ATC would reply with "Ding" and your amended clearance would be displayed. Push a button and reply....push a button and send it to the FMS.

No more stepping on people...nor getting stepped on. No more misinterpreting clearances. No more read backs or "thinking" you heard one thing, when the controler said something else.

I could live with that setup, especially since Roger from Chicago center retired. It's not the same old place without him.

 

[SiuDude]

I thought that too. I mean, FM radio is VHF, as is the aviation frequency range, no? Of course, I too know nothing about the mechanics of radio waves...

Nope, AM and FM refers to the type of sound modulation that is used by a certain radio - Amplitude Modulation and Frequency Modulation. VHF, UHF, HF, LF, 800mghz, etc., refers to the band used by a certain radio system.
Aviation is VHF AM. Most public safety radios, for example, are UHF, VHF or 800 FM.

 

[Kream926]

FN FAL

what you say is sounding alot like free flight. whats the deal with that i can never find any good articles on it?

 

[Stepclimb]

More on AM vs FM

I thought that too. I mean, FM radio is VHF, as is the aviation frequency range, no? Of course, I too know nothing about the mechanics of radio waves...

Within any frequency band, one can modulate a carrier signal in many ways; AM, FM, SSB (upper, lower) etc.
True, the US VHF commercial broadcast spectrum is modulated in FM from 97-108 MHz, but the aviation band above 108 MHz is AM. UHF (military aviation band) is also AM.
Back in the infancy of aviation radio, AM was simpler and therefore lighter. So it became the standard since it was around before FM. I don't think Frequency modulation even became popular until much later in the last century.
So now at this day in age, changing every radio in every aircraft and every ATC facility would not be cost-effective. Besides, AM has some advantages for aircraft use: namely signal quality vs. distance for a given transmitter power.

Also, with AM, one can cram more 'channels' into an existing spectrum with out worrying about 'bleed over', provided the transmitter can transmit narrowly and the receiver can filter accurately. (see my first post)
There are some other advantages to AM vs FM in aircraft use, but I can't remember them all. I'm sure there are some interesting articles on the subject floating around the web.
-Stepclimb

 

[FN FAL]

FN FAL

what you say is sounding alot like free flight. whats the deal with that i can never find any good articles on it?

With Slant/G, we are almost living in an age of "free flight", as long as we're in radar contact.

What I'm talking about, is secure digital data up-link. No more talking on static filled radios...we'll have digital signals relaying clearances, through push buttons. Heck, we got that here, right now, as we're talking amongst ourselves...why can't we have it with ATC?

Talking is going to consume too much time on radios and we don't have the bandwith to expand. The cops want more bandwidth, the fire and rescue guys want more bandwidth...ATC has, what they have (and what about those days when you hear Memphis Approach on Chicago Center and vice a versa?).

Frequency wars are just begining and 911 (not 9/11) is in a war with cell phones as we speak. Cops and Fire Fighters are in a situation now in some places, where their radios don't work because of cell phone towers.

Improved digital communications, will mean that a lot more signals can be sent over the same airwaves.

I'm all for ATC being digitized...to the point where clearances are push button...from aircrew to ATC and back.

For our communications, we need to acknowledge simple requests and ask for simple changes to clearances...but yet we have to talk about it. All of us know of the day when it took 12 conversations to get a sqawk code and an IFR clearance.

I'd like to push a button and get things going...without getting stepped on and without all the chatter.

 

[Kream926]

sounds like a great idea and im sure they are in the works. i would hate to see it eat jobs in the towers and centers tho. my plan B is airtraffic control. kinda like how top gun opened peoples minds to aviation, Pushing Tin did it for me for atc. as far the emergency services needing more nambwidth, i read somewhere that there's a bill that going up for vote to chrage people a dolla for 911 (not 9-11) cell phone calls. the reason in for better technology so they can pin point your location using cell phone. even tho i think they allready can do this.

sorry if this isnt flowing. im running on minimal sleep, finals.

 

[FL000]

Thanks for the AM/FM info y'all. I had no idea.