Grounding your electronic circuits...

[Chunkymonkey94]

I am planning to make a foxhole radio whenever I have the time but theres one thing I'm sort of confused about, that is how you are to ground the radio. I know that you can use radiators and cold water pipes but I don't have any of these thing to use as my ground. I want to know if you can just use a smaller piece of metal as you ground, like a washer or anything similar in size, and if so what kinds of metal can you use or does it not matter?
Thanks for the help! ^^

 

[crutschow]

Are you talking about an RF ground to make the antenna more efficient?

 

[Chunkymonkey94]

No I'm just talking about grounding in general.

 

[MikeMl]

No I'm just talking about grounding in general.

How is your "cell phone" grounded, your "calculator", your "automobile", your "flashlight"?

 

[JimB]

No I'm just talking about grounding in general.

Well, I am going to talk about your "foxhole radio" specifically, otherwise the subject is just too wide.

A foxhole radio is just a "Crystal Set" by any other name.
To work correctly, the radio needs an antenna, a length of wire which is as long and as high as possible.
It also needs and earth connection (ground connection).
The reason is that a small (very very small) current flows through the radio input circuit from the antenna to earth.
The better the earth connection, the more current will flow and the better the signal will sound.

If you do not have access to waterpipes, central heating radiators etc, you could use another length of wire similar to the antenna but running in the opposite direction from the antenna and connect that to the radio where the earth connection should go.
If you do that you have effectively made what is known as a dipole antenna.

If you want to try and use your foxhole radio outdoors (in a foxhole?) I suggest that you stick a short spike (6 to 12 inches long) into the ground (moist soil is best) and connect that to the ground connection on your radio.

A true story.
Some years ago I was out in the Scottish highlands and the guy with me was trying to listen to the cricket on the radio.
His radio was a little "Walkman" type thing and it just could not cut it.
So I got a length of wire out of the toolbox and strung it out and wrapped a few turns around the radio and then connected the end of the wire to a screwdriver which I stuck into the ground.
The guy was highly delighted to be able to listen to the cricket and I think he thought that I was some kind of magician/genius/miracle worker.

So, does this rambling missive help to clear your confusion?

JimB

 

[Nigel Goodwin]

So, does this rambling missive help to clear your confusion?

As kids we always used to listen to the top 20 on a Sunday night on the street. We soon found out if you put the radio near a telegraph pole it got MUCH better reception.

 

[unclejed613]

generally small (less than 1/8 wavelength in physical size) antennas work best if you maximize their effective surface area. for instance a "loopstick" antenna is very tiny (a few inches physically) antenna compared to the 200-600 meter wavelength of an AM signal. if you wind a multi-turn loop of wire a couple of feet in diameter (you've probably seen some of the old-fashioned "box-loop" antennas in old movies) and terminate the loop with an appropriate tuning capacitor, you have a "passive signal booster". you place an AM radio inside the loop with the loopstick antenna's axis perpendicular to the plane of the loop. then you tune the capacitor to peak the signal in the receiver. because the loop is larger, it intersects a larger portion of the desired signal, and inductive coupling between the loop and the radio passes that signal into the radio. this works ok with no physical ground because the induced current in the resonant loop creates a secondary field in the vicinity of the loop. loop antennas are very directional. you could increase the effectiveness of the loop if you ground one end of the loop and attach about 75-100 meters of wire to the other side of the loop. it's definitely something you could experiment with.

 

[Chunkymonkey94]

Could you use the negative terminal of a battery as ground?
If so would it work with the foxhole radio?

 

[JimB]

Could you use the negative terminal of a battery as ground?
If so would it work with the foxhole radio?

No.

The point of using an earth connection is to get some current flowing in the antenna circuit.

Connecting to some terminal of a battery will do nothing whatsoever.

JimB

 

[unclejed613]

there are two ways to get a good ground for your radio.
1) drive a copper pipe into the ground a few feet, and use a hose clamp to attach the ground wire.
2) lay a large metal plate (like 1 meter square or larger... the larger the better) on top of the dirt to capacitively couple to the ground below it. not as good as #1, but it is more portable.

if you use #1, one way to improve it's connection is to pour a pile of ice-melt salt (usually sodium or calcium chloride) on the ground where you will be putting the pipe in, and dissolve the salt into the ground with water. this is the method we used in the army, but be aware it will corrode the copper. that method might even improve the ground conductivity under the plate in method #2. soaking the salt into the ground should not be done in an area where there is grass or other plants (unless you need to clear some weeds also).

 

[Chunkymonkey94]

How do they ground portable radios that don't have a wire to the physical ground?

 

[MikeMl]

Portable radios that receive AM frequencies have enough gain that even a wet noodle without a counterpoise (ground) will pick up stations.
Line-powered radios sometimes use the ground wire in the electric service as a "counterpoise" for the receiving antenna.

Your single stage (crystal set?) radio only works if the antenna is absolutely the best that it can be, which carries with it the requirement that either the radio is at the center of a 1/2 wavelength dipole antenna (~100meters long) or connected between a 1/4 wavelength monopole (~50meters long) and a very good earth ground consisting of a 2 meter metallic rod driven in the earth...

Your original question about "grounding electronic circuits" was very ambiguous. It should have said something about "grounding an antenna", which is something quite different.

 

[JimB]

How do they ground portable radios that don't have a wire to the physical ground?

In addition to what Mike said above:
A modern (made in the last 50 years!) medium wave portable radio uses a ferrite rod antenna (I think this is often referred to as a "Loopstick" antenna in the USA) which receives the magnetic component of a radio wave rather than the electric component which is received by a wire antenna.
A ferrite rod antenna does not need a ground connection.

A VHF portable radio uses a rod antenna and the "ground" is provided by the rest of the circuit of the radio.
Not a very efficient way of working, but it gets by.

JimB