Understanding the Physics of an iHome System: Kiril's Story

[fourinone]

Hey there,
I have an iHome system and when I plug an AUX cable into the line out/in port(or for that matter just plug it in on one end and complete the circuit with my body) it sometimes picks up a local indian music station. While I don't mind the music, I am confused as to why it happens and my rudimentary knowledge of physics isn't enough to explain it. When I touch the little port that connects the iPod to the speaker system, it significantly lowers the volume of the radio. Is this because my body is acting as a resistor? When I connect a piece of tin foil to the same iPod port and touch the tin foil it has the same effect. However, when I plug just one end of the Aux cable into the iHome and touch the other end I get a very strong radio signal.
Sorry if this question is too basic to answer, I just didn't know where else to get a knowledgeable response :)
Kiril

 

[Antiphon]

The engineers who designed tube stereos 70 years ago prevented this by inserting a large resistor in series with the input stage. This created a lowpass filter when combined with the natural input capacitance of the first tube's grid.

Now, products are engineered by selecting a chip that integrates as many functions as possible and then using the manufacturer's reference design directly. There may be little or no actual electrical engineering going on in the manufacture of your speaker. Or perhaps to lower the cost they hired an inexpensive inexperienced engineer who didn't know that the problem existed much less how to avoid it.

Welcome to 2012.

 

[fourinone]

Is there any pragmatic way for me to fix that problem? When I hold onto the port for the ipod it doesn't create the interference. Is there a way to jerry rig a resistor that i can attach to the ihome to use when I want to use an AUX cable?

 

[jim hardy]

i have no idea what is an ihome and heard once of ipods from grandkids.

But it's apparent your port is detecting the radio station's signal. Let me guess- it's an AM station not far away?

Your body is acting as a capacitor which shorts outthe radio signal when you touch the port
and when you touch end of wire acts like more antenna

see is a 100 picofarad (100pf) capacitor, probably 79 cents at Radio shack, connected across the "port" gets rid of the interfering radio station..

perhaps somebody who's more familiar with modern stuff can help with mechanical connection details.

 

[alphysicist]

Hi Kiril,

Thank you for sharing your experience with your iHome system. It sounds like you are experiencing some interesting phenomena involving radio signals and your body's interaction with the iHome's AUX port.

First, I would like to clarify that when you touch the port with your body or a piece of tin foil, you are acting as a conductor rather than a resistor. A conductor is a material that allows electricity to flow through it easily, while a resistor is a material that restricts the flow of electricity. In this case, your body and the tin foil are conducting electricity and altering the radio signal.

Now, to explain why this is happening, we need to understand a bit about how FM radio signals work. FM radio signals are electromagnetic waves that travel through the air and are picked up by radios. When you touch the AUX port with your body or tin foil, you are acting as an antenna and picking up the radio waves. This is why you are able to hear the Indian music station.

When you touch the port with just one end of the AUX cable, you are creating a complete circuit for the radio waves to flow through. This amplifies the signal, making it stronger and easier to pick up. This is why you are getting a stronger radio signal when you touch just one end of the cable.

As for why touching the port with your body or tin foil lowers the volume of the radio, it could be due to a phenomenon called "capacitive coupling." This is when a conductive material, such as your body or tin foil, affects the electrical properties of nearby circuits. In this case, your body or the tin foil may be acting as a capacitor and altering the flow of electricity through the iHome system, resulting in a decrease in volume.

I hope this helps to explain the physics behind your experience with your iHome system. Keep exploring and asking questions – that's what science is all about!