88-108mhz--> F.M 108-130mhz-->A.M ?
i have a small doubt.the band 88-108mhz is F.M. right? when we take the same FM radio and cutoff a few turns off their oscillator the frequency moves up, say to 108 to 120mhz. it seems they call this 108-120mhz band as A.M. aircraft band. how come? we have taken a fm receiver and moved up the frequency. then it should be FM aircraft band. how did it change from FM to AM ? this is my doubt. please clarify.
You should post this in elementary electronic question section.
FM means Frequency Modulation and AM is Amplitude modulation. Use wikipedia to find out more.
i am not asking the definitions. my question is when a fm receiver(88-108mhz) is modified to receive 108- 120mhz, this is called aircraft band. they say aircraft band is AM. but, we have taken a FM receiver and moved it up to 108-120mhz. so, this should be FM. but, it is called AM aircraft band.WHY? how the FM band change to AM when the frequency is increased?
here's the site which tells how to convert a standard FM radio to receive AM aircraft band signal.
www.make-digital.com/make/vol09/?pg=29
Hi Deepak007,
The very first sentence in the paper u've sent clears u'r doubt. AIRCRAFT SIGNALS ARE BROADCAST IN AM FORMAT.
Here is my explanation: Please remember that as per ITU regulations, FM broadcast band is from 88-108MHz.But, if u r given permission, u can transmit FM signals on any freq. other than the std. freq.range used for radio broadcast.
Having said that, the same logic also applies for transmission of AM signals.Eventhough AM broadcast band is from 540-1650KHz, u can stll transmit AM signals in other freq. othan than the std.broadcast band.
The modulation technique assigned to transmit Aircraft signals is AM.But these signals can be txd. in any freq.range - in this case it is 108 to 138MHz(as per ITU regulations),which is the aircraft band and NOT the standard AM broadcast band.
Hope u got my answer.
Regards
Bhanumurthy.
Article you posted claims two modifications, one is moving receiving frequency range by spreading tank coil and second is to allow amplitude demodulation by detuning IF tank. I am not sure how it works and article does not post any details.
So, acording to article, you are enabling your receiver to listen AM signals with detuned FM receiver.