Interference

[Roger Dewhurst]

I recall reading that if an AM radio is tuned to frequency x plus or
minus the heterodyne frequency a radio tuned to frequency x will be
blotted out. Is this true? If so what is the heterodyne frequency?
Will it work with FM?

 

[Don Bruder]

I recall reading that if an AM radio is tuned to frequency x plus or
minus the heterodyne frequency a radio tuned to frequency x will be
blotted out. Is this true?

If you're speaking purely about receiving rigs, POSSIBLY... (but
probably only under very specific conditions) for a TX/RX rig, the
situation changes drastically.

If so what is the heterodyne frequency?

I'm quite sure you'll find that varies from radio model to radio model.
There's nothing "magic" about it - It's just the frequency the designers
picked for the heterodyning process. In theory, it could be any
frequency the designers care to choose. In practice, there are some
limitations (imposed by both the laws of physics, and the available
parts to build the beast) on what frequencies can be used with a given
reception frequency range to get decent results.

Will it work with FM?

See first answer.

 

[Roger Dewhurst]

If you're speaking purely about receiving rigs, POSSIBLY... (but
probably only under very specific conditions) for a TX/RX rig, the
situation changes drastically.

I am talking about off the shelf transistorized receivers which usually,
here at least permit reception of both AM medium wave and FM.

I'm quite sure you'll find that varies from radio model to radio model.
There's nothing "magic" about it - It's just the frequency the designers
picked for the heterodyning process. In theory, it could be any
frequency the designers care to choose. In practice, there are some
limitations (imposed by both the laws of physics, and the available
parts to build the beast) on what frequencies can be used with a given
reception frequency range to get decent results.


See first answer.

I see no mention of FM in the first answer.

R

 

[Wim Lewis]

I recall reading that if an AM radio is tuned to frequency x plus or
minus the heterodyne frequency a radio tuned to frequency x will be
blotted out. Is this true?

The idea is that the first radio's LO is leaking and will interfere with
the signal? I guess I don't see why that wouldn't happen, if the first
radio is poorly made and/or the signal is weak.

If so what is the heterodyne frequency? Will it work with FM?

I think it's usually 455 kHz for AM and 10.7 MHz for an FM receiver, but
as another poster said, it's entirely up to the radio's designers.

An FM receiver might be less susceptible to this kind of interference
because of the FM "capture effect". Or maybe it would me more susceptible.
I dunno.

 

[Don Bruder]

I am talking about off the shelf transistorized receivers which usually,
here at least permit reception of both AM medium wave and FM.

I see no mention of FM in the first answer.

R

Use a brain-cell, dude...

 

[Roger Dewhurst]

---
Is the second radio you mentioned the first radio you mentioned?
---



JF

No. A is driven mad by continual noise from the radio of B. A would
like to deter B from keeping his radio switched on all day.

R

 

[Roger Dewhurst]

Use a brain-cell, dude...

My brain cells work OK when applied to matters I know something about.
I doubt that your brain cells would be much use in dealing with matters
that I know something about however well they may work in relation to
matters you know something about. e.g. I imagine that all you know
about proving up uranium ore reserves in sedimentary rocks could be writ
large on the back of postage stamp.

R
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