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AM/FM Radio difference????

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Old 05-13-2003, 06:20 PM
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Eagle delta
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Default AM/FM Radio difference????

I am wondering what the difference is between an AM radio and FM radio besides cost, is it the range or something????
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Old 05-15-2003, 04:04 AM
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Default AM/FM Radio difference????


To the best of my knowledge, the biggest difference (aside from cost) is FM is less succeptible to interference. AM may have less range, but it's still further than you can see.

From my perspective, it's Old Technology versus New Technology.

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Old 05-15-2003, 04:32 AM
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Default Little differance.

Have never had a problem with reception with AM or FM, old or new. With the square wave signal, wonder if it AM/FM is even an adequate term? I know some have stated that technically there is no reason FM would be better than AM. AM doesn't need to be dual conversion to be narrow band, but I don't think FM has to be either????? Need some experts here? Have a Hitec 3 channel that is AM. No problems with it.
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Old 05-15-2003, 04:37 AM
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Default AM/FM Radio difference????

I heard somewhere (cant remember) that FM radios are cheaper to manufacture than AM, don't know if it's true or not.
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Old 05-15-2003, 04:43 AM
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Default AM/FM Radio difference????

Originally posted by Pilotsmoe
I heard somewhere (cant remember) that FM radios are cheaper to manufacture than AM, don't know if it's true or not.
Why are the 3 channel AM recievers cheaper than FM 3 channel recievers?
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Old 05-15-2003, 01:02 PM
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strato911
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Default Re: Little differance.

Originally posted by Sport_Pilot
Have never had a problem with reception with AM or FM, old or new... AM doesn't need to be dual conversion to be narrow band, but I don't think FM has to be either?????
As I said, AM range still exceeds your abilty to see what the plane is doing. I still use AM for one of my planes.

Single / dual conversion - ALMOST ALL current JR recievers are single conversion, and they are all narrow band.
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Old 05-15-2003, 01:12 PM
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Default AM/FM

Between my Futaba and JR radios I have about 20 radios and many of them are Am with some single conversion receivers.
I fly in rural Pa so I see no difference. No discussion on AM/FM is complete untill you read the terrific posting from the Torrie Pines club at
www.torreypinesgulls.org/Radios.htm
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Old 05-15-2003, 01:27 PM
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Default AM/FM Radio difference????

Here's a brief description of AM vs. FM reprinted from A science Odyssey.

FM radio works the same way that AM radio works. The difference is in how the carrier wave is modulated, or altered. With AM radio, the amplitude, or overall strength, of the signal is varied to incorporate the sound information. With FM, the frequency (the number of times each second that the current changes direction) of the carrier signal is varied.

FM signals have a great advantage over AM signals. Both signals are susceptible to slight changes in amplitude. With an AM broadcast, these changes result in static. With an FM broadcast, slight changes in amplitude don't matter -- since the audio signal is conveyed through changes in frequency, the FM receiver can just ignore changes in amplitude. The result: no static at all.



As you can see, FM is superior to AM for noise/interference masking, but, as others have said, our receivers are almost always in complete saturation, so it becomes a moot question except in high noise areas, then FM is the choice.
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Old 05-15-2003, 02:33 PM
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Default AM/FM Radio difference????

FM signals have a great advantage over AM signals. Both signals are susceptible to slight changes in amplitude. With an AM broadcast, these changes result in static. With an FM broadcast, slight changes in amplitude don't matter -- since the audio signal is conveyed through changes in frequency, the FM receiver can just ignore changes in amplitude. The result: no static at all.

The amplitude changes on AM to make the music and voice that we hear. But the square wave output is a constant frequency so the AM wave amplitude doesn't change. So there is no noise or static differance with AM and FM with our radios.
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Old 05-15-2003, 03:21 PM
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Default AM/FM Radio difference????

Yes, the quote referred to voice/music broadcast AM which is susceptible to noise as the carrier level changes with the modulation peaks.

Even though R/C AM equipment is basically driven to full power by the encoding modulation, the received AM signal can still be affected by nulls and mixes allowing noise to enter the receiver.

I agree that there is little difference between the two, however FM still has the greatest ability to cancel noise under adverse conditions.
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Old 05-15-2003, 03:52 PM
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Default AM/FM Radio difference????

AM vs. FM

My thumbs can't tell the difference.

I have a 1990 Futaba gold sticker Conquest in a Magic and never got a hit. The tail taps are just as easy on AM
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Old 05-16-2003, 01:52 AM
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Default AM/FM Radio difference????

"Even though R/C AM equipment is basically driven to full power by the encoding modulation"

Not quite so.Actually the signal is switched off by each square pulse of the modulating (encoder) signal. Exactly opposite to a CW signal,which is switched ON by each Dit or Dah of the Morse key.An AM R/C transmitter puts out almost twice as much power WITHOUT the encoder signal. Unlike an AM voice signal(which is at one half power until modulated.The question of interference has no resemblance to a voice transmission (EXCEPT when being overpowered by a stronger signal,i.e. a closer transmitter on the same channel).
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Old 05-17-2003, 05:19 AM
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Default AM/FM Radio difference????

We are comparing apples and oranges. I would agree that AM can be nearly as reliable and interference free as FM, but FM has taken over and the innovation went with it. An FM receiver 20 years ago probaby was not a whole lot better than its AM brother, but FM kept on improving, and your AM design is basically still 20 years old.

Also, many (but certainly not all) AM receivers produced back then were wide-band, not narrow-band. When the FCC made us narrow band, they sold channels between our 72 mHz RC channels to industry. Thus, your old wide-band receiver can be shotdown by adjacient users operating cranes and such.

Many AM receivers were also produced narrow-band, they don't have this problem.

AM is cheaper to produce than FM. It uses less parts.
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Old 05-17-2003, 12:58 PM
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Default They still make AM!

Bought one on channel 30 two years ago. It works just as well. IMO its a non issue. The FM sets are not really FM read the link from Cassidy!
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Old 05-17-2003, 02:33 PM
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Default AM/FM Radio difference????

That link is interesting, and has been discussed in many prior discussion threads. It even mentions George Stiener, which is interesting given that George Stiener probably disagrees with much of the article. I disagree with much of the article as well. We can not believe everything in print, electronically or dead tree. Many do not believe what I say, but I continue to tell what I know. Good luck. We can all agree to disagree.
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Old 05-17-2003, 03:51 PM
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Default MO_Radio_Tech

What is wrong with the following:

In R/C "AM" there are only two states -- FULL signal and NO signal, nothing in between. R/C AM is more PM. Seriously, a more descriptive term would be Pulse Modulation, but that looks like PPM sans a P. How about AM being BM -- Binary Modulation.

Likewise, true Frequency Modulation implies servo position proportional to the carrier frequency moved up or down a little, so full left on 72.070 MHz carrier (channel 14) would be 72.075 (carrier + 5 Khz), neutral at 72.070 and full right 72.695 (carrier - 5 Khz). In R/C "FM" there is only full modulation i.e., carrier shifted by 5 Khz or NO modulation (carrier only). R/C FM is identical to wireless data transmission "frequency shift keying" (FSK), at least the computer people don't pretend to be FM.


Looks accurate to me.
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Old 05-17-2003, 08:08 PM
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Default AM/FM Radio difference????

I guess I should go back to using a wagon wheel because it is better than the modern tire. I just love it when the anti-PCM, anti-PPM folks start arguing. Get out your twice daily, wide-band hand-tuned vac-tube gear and shoot all of us narrow band folks down. Teach us a lesson!!! You think just because an article has a bit of techno-jargon it has to be true. Many of the details in this article are correct, but his conclusions are flawed.

I am just going to leave it at that, because I am tired of the pi$$ing matches in this board.
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