Can FM receiver hear AM signals

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skyler440

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I heard at one point that an FM reciever will be able to pick up AM radio signals.

•Can I pick up audible airplane signals from my 2 meter ham radio, which receives down to 118 megahertz?

•What frequency should I start with if I am in the Denver CO?
 

majoco

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One of the major advantages of FM is it's immunity to amplitude variations such as ignition noise. This is because in a limiter stage in the receiver the signal is clipped off top and bottom - any amplitude variation is clipped off with it. The frequency modulation variations are still there and are made back into audio in the discriminator stage.
 

w2xq

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Dunno what 2m radio you are using but you need to check the manual. My Yaesu FT-8800R and VX-6R defaults to AM when entering aero frequencies. Reception is good; I just adjust the squelch. HTH.
 

ka3jjz

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Moved this to the aircraft forum since it has nothing to do with freqs below 30 Mhz...

On the contrary - if the radio in question tunes down to the 118 Mhz area without any kind of trickery, chances are that it has a AM detector in line somewhere.

The little duckie is not likely to hear very much - the antenna is very inefficient here - but it can be done.

I had a VX5R for some time and had no problem listening to BWI (I lived very close to it at that time) approach/departures and other AM based sigs...Mike
 

MBill

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AM on FM

Skyler440's question takes me back to when I was a kid. I use to modify am/fm radios by stretching
the RF coils in the FM section. You could then hear AM aircraft signals if you tuned carefully. Of
course, there were just a few and only from aircraft overhead or close to my location. Had one Sears
AM/FM transistor portable that would pick up aircraft in between the FM stations without any
modifications; again they had to be nearby aircraft. You had to have an analog tuning dial too, not the
digital ones as of today. I still see some articles on the net showing how to do it.
 

N9JCQ

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I had the TM-241 and the oddity with that radio is that you have to turn the squelch all the way off to hear aircraft. I called Kenwood to confirm this and the tech on the line said it was true. I thought that this was really odd. How can you scan memories if some of them are in AM and are aircraft? Its annoying at the very least. I have an FT-7800 dualbander now and that think rocks on civil and Military aviation freqs. So yes, you can hear aircraft with the TM-241 but you need to turn the squelch off and listen to the static too.
 

LtDoc

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Can an FM radio 'hear' AM? Not likely at all, but an AM radio can 'hear' FM if you want to bad enough. Not well by any means, but you can understand it.
- 'Doc
 

TassieJay

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Actually... yes you can hear & resolve AM on an FM receiver. There's a few catches though.
With a narrowband FM receiver, the result will be very distorted, readability about 1. The situation can be improved by tuning to the very edge of the signal, if your rig can tune in fine enough steps; this results in copy that's still distorted, but listenable. Readability: 2.
If you can widen your FM bandwidth, using WFM (or a bandwidth suitable for broadcast FM reception) then tune to the edge of the signal, the AM signal actually becomes quite intelligible. In the two receivers I've tested this on, it works about 90% as well as it's AM mode. Definitely readability 4 or 5.That's not going to be much good if you have a lot of closely spaced AM signals, obviously.
 

jcj

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I had a TM-741 for years (multiband version of the TM-241). i believe it had identical 2M circuitry. It came from factory with extended range receive and indeed did default to AM mode for all frequencies below 136 MHz (although you could change it to FM).

The squelch did work for AM & FM modes although I think the squelch quieting threshold for AM was still open squelch on FM (the thresholds were different. I didn't really use it to scan but I think it would as long as the squelch was set above the squelch break threshold for both AM and FM.
 

Thayne

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It was fairly common in the late 50's-60's to use AM surplus military receivers to listen to high band FM by retuning by various modifications to reach the 150 MHZ area then using " slope detection" which was tuning the receiver slightly either side of the FM station. Some of that military stuff did not drift hardly at all.
Of course, now we have expensive toys to help us---
 
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