2018-04-22 Ferrite Loopstick Basics

From FB group Building Transistor Radios

Then there is the loopstick. It is deliberately made long and thin to capture the RF magnetic fields. The frequencies that loopsticks are better at capturing are those that require long antennas that would be impractical. So the AM broadcast band is where loopsticks do their best. The loopstick’s ferrite mix is optimized for this band. If the frequencies are higher, the ferrite’s losses increase and the wavelengths become short enough to where reasonably sized whip antennas can do a better job. The ferrite’s mix may work at higher frequencies but not as efficiently, and as the frequency goes higher the efficiency goes down and losses go up.

Jim Glover
I’ve seen antenna terminals connected to a few turns of wire wrapped around the loopstick. I should also say that the AM broadcast band has a lot of natural noise so adding more gain to the radio will amplify that noise along with the signals. If an antenna is added, more signal will be captured and you can then hear the signal, where before you only heard noise. But if the antenna signal is out of phase with the loopstick signal, they will subtract and you lose some signal. The radio can be repositioned to make the signals add.

If you use a decent sized (larger) antenna, it can pick up more signal than the loopstick because the antenna is physically larger. But since the noise level is higher at MFs (0.3 to 3 MHz) the antenna doesn’t have as much benefit as one at higher frequencies.

Also, there tends to be a lot more man-made noise inside. So putting the antenna outside helps to get away from some of that man-made noise.

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