On Thu, 05 Jul 2007 18:07:22 -0700, Radium
wrote:

On Jul 5, 3:19 am, "Mike Kaliski" wrote:
"Radium" wrote in message

oups.com... Hi:

Can the Spin Exchange Relaxation Free Magnetometer be used to receiver
distant AM radio signals in which the carrier frequency is 150 KHz?
What if the carrier frequency is 44.1 KHz [for the same reason CDs use
a 44.1 KHz sample rate]? 40 KHz?

Thanks a bunch,

Radium

Radium,

The simplest answer is no. The reason is that you specify 'distant'. The
strength of a magnetic field decays rapidly with distance and for most
practical purposes, 800 metres would be a maximum typical detection range
for man made magnetic fields as opposed to natural fields like the earth's
magnetic field.

A radio signal has an H-field component that doesn't decay like a
near-field magnetic effect. That's why AM radios use loop or rod
antennas that pick off the magnetic component of the em wave.


Radio waves are made up of electric and magnetic fields.

Yes.


Couldn't the Spin Exchange Relaxation Free Magnetometer receive the
magnetic portions of AM radio waves at the carrier frequencies I
described? If not, why?

This might be made to work, but gaseous resonances like this are
usually very low bandwidth detectors, often sub-Hz, so sensitivity at
tens of KHz would be pitiful.

RF Reception in this frequency range is dominated by atmospheric
noise, so a super-sensitive detector doesn't help. A simple tuned loop
antenna and a decent front-end amp, a jfet maybe, is as good as you
can do.

John