Spaceclam

Will a small magnet about 6" away from a receiver antenna cause any trouble? it would be a weak magnet, like that flexible rubbery stuff that you use for refrigerator magnets. Would that cause any trouble?

wisdom-seeker

Probably not. If you were talking about a magnet right on the receiver, it would be another story. A magnetic field close (in contact with) to a receiver would change how any of the inductive components in the receiver would work.

Rodney

Absolutely no effect, even if sat right on the reciever. The only way it would effect the radio would be to have it moving relative to the radio at a very high frequency like thousands of cycles per second and even then it would be doubtful.

wisdom-seeker

Even a static magnet field will affect an inductor. The field moves the inductor closer to magnetic saturation (or further away depending on field polarity). However, in either case, it can influence the frequency resonance of an LC circuit. At least that what my EE professor said back in 1972. I don't think physics has changed since then. I have seen a practical demo of this on an FM box destined for a satellite. The box would quit working when the EM field of the shake table was powered up, before the shaking started. We had to solve that one by mounting the box on a long standoff to get it out of the magnetic field. The shake test was to see if the FM box would survive a rocket flight.

XJet

But the coils in a receiver operate *so far* away from the saturation point that even an extremely strong magnet would have no perceptable effect.

Rodney

Wisdom-seeker, there is a big difference between an electomagnetic field and a magnetic field.
with some 40+ years experience in instumentaion, RF, and guidance systems, I can still assure Spaceclam that NO EFFECT will occur with the magnet right on his receiver case. Yes shakers do create an interferance problem if every thing is not set up properly but that was not Spaceclams question.

dirtybird

My Feedback: (5)

I agree that there will be no effect on on the receiver with the magnet
I am curious, though, as to the difference between an electromagnetic field an a magnetic field. Please explain. All of this time since I graduated from E.E. college I thought they were the same.

hebertjj

Dirtybird,

Apparently Rodney went to school before the GUT. Or he's talking about an AC mag field (as with a shaker motor) vs. a fixed mag field. Now do you know the difference between the weak force and the strong force?

RunningMan

Well, a static magnetic field has only a B vector present, and an electromagnetic field has B and E vectors at 90 degress to each other. Anything else will not propagate. They don't teach this in EE, you have to take Electrodynamics in a Physics course to get this type of abuse.[&:]

Steve

Rodney

Thanks running man, you beat me to it. Rodney

dirtybird

My Feedback: (5)

OK I never had electrodynamics. I don't think they had such when I went to school. But I do notice that they tend to use PM and electromagnets interchangeably such as the magnet for a magnetron or for a DC motor. I don't think it has much effect on the initial question of this thread.

backfire

Well, I placed a small strong horseshoe magnet on the bottom of a Hitec 8-channel dual conversion receiver and it shut down. Same thing happened with a Hitec 555. Magnets are often used to alter the saturation characteristics of ferrite based inductors for specific purposes; and strong magnets can certainly affect some receivers. I would be careful using a powerful rare-earth magnet (such as is sometimes used for hatches) near a receiver. A couple of inches away should do it. A strong magnet near a ferrite bead or toroid used for noise reduction might also be an issue.

And; RunningMan,

I don't know who the EE's are that you might know, but the relationship between magnetic and electric fields was basic field theory in my EE curriculum - and that was 39 years ago!

dirtybird

My Feedback: (5)

I think I am going to drop out of this thread. When we start to argue about whats in an EE education we have lost our way.