AM frequency ??? Questions  
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AM frequency ??? Questions - 9/23/2008 3:30:20 AM   
XLEEM


 

Posts: 12
Joined: 8/8/2008
From: , ID, USA
Status: offline 		What is the difference between AM and FM channels. I was looking at a really good deal with an engine, all servos and radio gear and airplane for pretty cheap but the owner said it was AM. Is this any different good or bad or what? Thanks Xleem
       Post #: 1

RE: AM frequency ??? Questions - 9/23/2008 4:04:34 AM   
wings



Posts: 1541
Joined: 8/23/2003
From: Carrollton, KY, USA
Status: offline 		Both AM and FM use the same 72Mhz frequency band.


FM signal changes the frequency back and forth between the carrier frequency and a shifted frequency that is very close the the carrier frequency.


An AM signal has a constant frequency but the signal is turned on and off to modulate or the signal.

Modulation is just a fancy word that means the transmitter transforms your stick movement into a language that the receiver understands. It's kinda like Morris code.


It's called Pulse Code Modulation. I explain it more in-depth here on my website.


AM uses signal on or off to represent pulses. FM switches between two frequencies to represent the pulses on or off.

Most radios today are FM.(or spread spectrum) Some say AM is more prone to interference, although I'm not 100% convinced that is accurate.

AM transmitters are limited to four channels, that's probably the biggest drawback I see.

If it's a really good deal I'd say get it. They work just fine.

But if it's a mediocre deal I would hold off and get FM or 2.4Ghz.

I hope this helps.










< Message edited by wings -- 9/23/2008 4:06:31 AM >

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(in reply to XLEEM)
       Post #: 2

RE: AM frequency ??? Questions - 9/23/2008 4:27:49 AM   
XLEEM


 

Posts: 12
Joined: 8/8/2008
From: , ID, USA
Status: offline 		Thanks I appreciate the advice. I think I'll opt to get it.

(in reply to wings)
       Post #: 3

RE: AM frequency ??? Questions - 9/23/2008 5:13:24 AM   
Campgems


 

Posts: 2107
Joined: 2/18/2006
From: Arroyo Grande, CA, USA
Status: offline 		It depends on the frequency. If it is a narrow band AM in the 72mhz band, it will probably be OK. I wouldn't put it in a 1/4 scale, but for close in flying it should be OK. If you want more than a 4 channel setup though, I would go with the FM or PCM radios or if the pocket book will allow, a 2.4GHz setup.

The AM is old iron. Doesn't mean it won't work, but it won't have any of the neat stuff avaiable now. Like dual rates, amd expo, let alone any computer mixing. It is pure basics, maybe with reverse on the servos. I have a Futaba FG series TX and Rx in front of me that has the gold ama sticker, A mandatory valadation to fly at any club field. It even has a RF module for the TX so you can easly change frequencys, if you can find another.

IF, and it a big IF, the Tx and the RX are compatable, Gold stickered, and you can get it for $20 or so, it may make a good first radio. You will have to get new batteries, which will run you anothe $40 to $60 bucks or so.

My suggestion would be to pass it up and spend the money on a more current radio. Nothing like a radio failure on your first flight to sour the experience. For under $200 you can get a new 6 chan computer radio with receiver and four servos. http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRXF5**&P=SM

It's hardly worth putting up with the headaches of the old iron.

Don

(in reply to XLEEM)
       Post #: 4

RE: AM frequency ??? Questions - 9/23/2008 5:19:03 AM   
JohnW



Posts: 1770
Joined: 3/22/2002
From: Lincoln, NE, USA
Status: offline 		Agree with camp. Get the plane if you want it and it is a good deal, but if it was me, I'd ditch the radio.

(in reply to Campgems)
       Post #: 5

RE: AM frequency ??? Questions - 9/23/2008 11:04:04 AM   
flyX


 

Posts: 644
Joined: 7/24/2007
From: el centro, CA, USA
Status: offline 		I didn't have any problems with an AM radio . I purchased it with a a used model.
It was an old airtronics. It had a gold AMA inspection sticker on it.
I flew the model until i crashed it....it was the radio and not pilot error

The radio system that comes with R/C cars are AM. And don't say a $500 savage is worth less than a $500 airplane.lol

< Message edited by flyX -- 9/23/2008 11:06:42 AM >

(in reply to JohnW)
       Post #: 6

RE: AM frequency ??? Questions - 9/23/2008 11:05:38 AM   
flyX


 

Posts: 644
Joined: 7/24/2007
From: el centro, CA, USA
Status: offline 		sorry...


< Message edited by flyX -- 9/23/2008 11:06:19 AM >

(in reply to flyX)
       Post #: 7

RE: AM frequency ??? Questions - 9/23/2008 11:12:24 AM   
Missileman



Posts: 3104
Joined: 2/14/2006
From: Algonac, MI, USA
Status: offline
quote:

ORIGINAL: flyX

I didn't have any problems with an AM radio . I purchased it with a a used model.
It was an old airtronics. It had a gold AMA inspection sticker on it.
I flew the model until i crashed it....it was the radio and not pilot error

The radio system that comes with R/C cars are AM. And don't say a $500 savage is worth less than a $500 airplane.lol

Yes but a $500 Savage isn't going to fall out of the air and cause possible property damage or injury to bystanders if it loses a signal.Nor is it operated from a great a distance as airplanes are.

< Message edited by Missileman -- 9/23/2008 11:13:28 AM >

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(in reply to flyX)
       Post #: 8

RE: AM frequency ??? Questions - 9/23/2008 1:31:43 PM   
flyX


 

Posts: 644
Joined: 7/24/2007
From: el centro, CA, USA
Status: offline 		I garantee ya, if you ever had a runaway savage going into traffic...you'll have a differenent perspective.
Or if you ever been hit by a 15lb object going 40-45 mph.

There's a fail safe incase of runaways (Low batteries or antenna not being raised).
It dosen't came out of the box.

< Message edited by flyX -- 9/23/2008 1:45:47 PM >

(in reply to Missileman)
       Post #: 9

RE: AM frequency ??? Questions - 9/23/2008 3:04:14 PM   
bruce88123


 

Posts: 10738
Joined: 11/26/2004
From: Memphis, TN, USA
Status: offline
quote:

ORIGINAL: wings

Both AM and FM use the same 72Mhz frequency band.


FM signal changes the frequency back and forth between the carrier frequency and a shifted frequency that is very close the the carrier frequency.


An AM signal has a constant frequency but the signal is turned on and off to modulate or the signal.

Modulation is just a fancy word that means the transmitter transforms your stick movement into a language that the receiver understands. It's kinda like Morris code.


It's called Pulse Code Modulation. I explain it more in-depth here on my website.


AM uses signal on or off to represent pulses. FM switches between two frequencies to represent the pulses on or off.

Most radios today are FM.(or spread spectrum) Some say AM is more prone to interference, although I'm not 100% convinced that is accurate.

AM transmitters are limited to four channels, that's probably the biggest drawback I see.

If it's a really good deal I'd say get it. They work just fine.

But if it's a mediocre deal I would hold off and get FM or 2.4Ghz.

I hope this helps.


Where did you get the idea that only 4 AM channels are available? I have a couple of Futaba AM's with 6 and 7 channels. If speaking of 4 freqs/channels within the band, that is also not true. Not current production but still out there.

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(in reply to wings)
       Post #: 10

RE: AM frequency ??? Questions - 9/23/2008 3:58:28 PM   
EloyM


 

Posts: 204
Joined: 8/5/2002
From: Santa Ana, CA, USA
Status: offline 		Morris Code? MORRIS code?????

(in reply to wings)
       Post #: 11

RE: AM frequency ??? Questions - 9/23/2008 4:27:30 PM   
bruce88123


 

Posts: 10738
Joined: 11/26/2004
From: Memphis, TN, USA
Status: offline
quote:

ORIGINAL: EloyM

Morris Code? MORRIS code?????

Yeah, he was Morse's cousin I think. On his mothers side. http://en.wikipedia.org/wiki/Morse_code

< Message edited by bruce88123 -- 9/23/2008 4:29:35 PM >

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3-D is for Monster Movies

(in reply to EloyM)
       Post #: 12

RE: AM frequency ??? Questions - 9/23/2008 8:34:17 PM   
wings



Posts: 1541
Joined: 8/23/2003
From: Carrollton, KY, USA
Status: offline
quote:

ORIGINAL: bruce88123


quote:

ORIGINAL: wings

Both AM and FM use the same 72Mhz frequency band.


FM signal changes the frequency back and forth between the carrier frequency and a shifted frequency that is very close the the carrier frequency.


An AM signal has a constant frequency but the signal is turned on and off to modulate or the signal.

Modulation is just a fancy word that means the transmitter transforms your stick movement into a language that the receiver understands. It's kinda like Morris code.


It's called Pulse Code Modulation. I explain it more in-depth here on my website.


AM uses signal on or off to represent pulses. FM switches between two frequencies to represent the pulses on or off.

Most radios today are FM.(or spread spectrum) Some say AM is more prone to interference, although I'm not 100% convinced that is accurate.

AM transmitters are limited to four channels, that's probably the biggest drawback I see.

If it's a really good deal I'd say get it. They work just fine.

But if it's a mediocre deal I would hold off and get FM or 2.4Ghz.

I hope this helps.


Where did you get the idea that only 4 AM channels are available? I have a couple of Futaba AM's with 6 and 7 channels. If speaking of 4 freqs/channels within the band, that is also not true. Not current production but still out there.



I've been wrong before! I made that comment because I personally have never seen an AM radio with more than 4 channels. So I assumed that's all that was available. Guess I shouldn't assume things huh?

If you don't mind sharing, what are the models of those Futaba radios you speak of?


And Morris is my cat...

_____________________________

Are you Hooked on RC Airplanes?
Feed your addiction at: Hooked-on-RC-Airplanes.com

(in reply to bruce88123)
       Post #: 13

RE: AM frequency ??? Questions - 9/23/2008 9:43:21 PM   
bruce88123


 

Posts: 10738
Joined: 11/26/2004
From: Memphis, TN, USA
Status: offline
quote:

ORIGINAL: wings


quote:

ORIGINAL: bruce88123


quote:

ORIGINAL: wings

Both AM and FM use the same 72Mhz frequency band.