Crystal radio only buzzes

Thread Starter

Circuits123

Joined Dec 7, 2012
64
I bought a crystal radio kit and I'm having some trouble with it. Here's the kit.
My antenna is about 100ft of extension cord about 10ft off the ground between 2 trees. One end hangs down to make an L shape. To connect it to the radio, I took an old 2 prong cord and plug, cut off one off, soldered the wires together, and connected that to the radio with alligator clips. Then I plugged the other end into the hanging extension cord. For the ground, I used a long (20+ft) telephone wire since the trees are far from the house. I cut the jacks of both ends and soldered all the individual wires together. One end is connected to an outdoor hose bib and the other is connected to the radio with alligator clips. The unused length stays coiled on an oatmeal box. The green clip is the antenna/extension cord and the black clip goes to the ground. I've attached photos of everything. When I try it out, I hardly get anything. The best I get is when I touch my finger to either end of white clips. Any suggestions?
IMG_1365.JPG IMG_1366.JPG IMG_1367.JPG IMG_1369.JPG
 

Thread Starter

Circuits123

Joined Dec 7, 2012
64
I clicked POST too fast. I meant to add that the only sound I get is a buzz and it's only audible when I touch the white clips with my finger. Adjusting the variable capacitor has no impact, nor does disconnecting either the ground or antenna.
 

MrChips

Joined Oct 2, 2009
19,778
Do you know for sure that the GROUND is a metal pipe that goes into the earth?

Here is a simple test.
Forget the rest of the kit.

Connect the antenna to one lead of the diode.
Connect the GROUND to the other lead of the diode.
Connect the earphone across the diode.
You ought to hear something.



 

LesJones

Joined Jan 8, 2017
2,420
Are you sure that you have linked point 3 to EITHER point 1 OR 2 on the schematic. If not it will not work. (After seeing the picture of your construction I think you have made this connection. Note I am not sure how the track run in the breadboard as I have never used it.)
The fact that you get a buzz when you touch the top end of the coil suggests that you do not have a low frequency path through the coil to earth. Do you realise that the wire that the coil is wound with is insulated. You either have to carfully scrape off this insulation or sometime the insulation will burn off when you solder to this type of wire. (It depands on the type of insulation varnish used.) Check that you get a low resistance reading (Less than a few tens of ohms.) between all the connections that you think you have made to the coil.

Les.
 
Last edited:

dendad

Joined Feb 20, 2016
3,190
One point, the variable capacitor is not connected correctly.
Have a look at the circuit. The center pin and one outside pin is the way it should be.
Carefully check your circuit. Clip leads and bread board construction lead to bad joints.
From the instructions in the circuit...
"It is best to solder the coil wire, not doing so may cause a bad connection and the radio will not work."
 

danadak

Joined Mar 10, 2018
3,726
If you have triac based light dimmers in the house, turn those off. Also
Florescent lights. Even some LapTop power bricks cause a lot of EMI.

Try throwing the main breaker on your house to see if its your home creating
all the RFI. Then close main and breaker by breaker isolate loads that are causing
RFI. I have even found RFI from Ethernet cabling.

Regards, Dana.
 

Thread Starter

Circuits123

Joined Dec 7, 2012
64
Do you know for sure that the GROUND is a metal pipe that goes into the earth?
Here is a simple test.....
I have no idea if it goes into the earth, but when I try your test, I get a strong buzzing sound. Does that pass?

I tried shutting off all the power to the house too - no change.
 
Last edited:

MrChips

Joined Oct 2, 2009
19,778
I have no idea if it goes into the earth, but when I try your test, I get a strong buzzing sound. Does that pass?

I tried shutting off all the power to the house too - no change.
Check around your property and see if there are any power lines or power transformers in the vicinity.

I think your solution will require you to drive your own grounding rod into the earth.
 

Thread Starter

Circuits123

Joined Dec 7, 2012
64
Check around your property and see if there are any power lines or power transformers in the vicinity.

I think your solution will require you to drive your own grounding rod into the earth.
I'll try that. I've got a few acres and there's nothing within a few hundred feet
 
Crystal sets are pretty foolproof so the first thing I'd check is your normal radio reception. Are you in one of the rare areas where you don't have good reception from a local radio station?

Where is the station? Stand in your yard and face in it's direction. Lift your hands so you are pointing right and left. Try to run your antenna parallel to your hands.

Where the extension cord is attached to the tree, use a string loop so that the cord does not touch the tree. Do this at both ends.

I suppose your diode could be defective.

This is an interesting problem; please keep us informed.
 

Thread Starter

Circuits123

Joined Dec 7, 2012
64
I get a bunch of AM stations on a regular radio so I don't think that is the problem. The cord doesn't touch the trees on either end but it touches a branch in the middle. But it's insulated so does that matter? I've also tried more than one diode. I'll play around with the ground and antenna and see what happens.
 

BR-549

Joined Sep 22, 2013
4,938
Do you have a signal source to verify your tuning range? Can you pick up the local oscillator of a transistor am portable radio? Tune am radio to high end and low end of dial with volume muted.

Can you pick up any thing on the crystal? It will not be modulated.

Do you have a ground connection at room power receptacle? Your ground is fishy.

Are you sure the headphone is high Z?
 

Ylli

Joined Nov 13, 2015
854
Everyone has good suggestions, but let me try. Looking at the schematic here: https://www.mikeselectronicparts.com/wp-content/uploads/Crystal-Radio-Kit-2.pdf

Properly identify the leads of the ferrite loopstick, and make sure all the leads are bare and tinned. If you have an ohmmeter, use it to confirm continuity between all the leads. Note the pinout for the variable capacitor in the schematic. Connect lead "1" of the loopstick to the variable capacitor pin labeled "A". Solder it - make sure the solder flows smoothly, but be careful not to overheat the lead entering the variable cap. Now connect lead "4" from the loopstick to the capacitor pin labeled "G". Loopstick lead #4 and the capacitor pin "G" become the common ground, and other components that go to 'ground' go to this point.

Connect one lead of the diode to the junction of loopstick lead "1" and the variable capacitor lead "A". (this is one of those rare cases where the polarity of the diode really doesn't matter.) Connect the other end of the diode to one lead of the 47k resistor. Connect the other end of the 47k resistor to 'ground'. Now connect the 0.001 uF fixed cap in parallel with the 47k resistor - one lead to the hot side, the other to 'ground'. Do the same with the earphone.

Note, both the loopstick and the earphone may have 'funky' wires that are hard to solder. when connecting them be sure you make good connections.

Now for the antenna and physical ground. The ground you described in your original post is a no-go. You need the ground to be as short as possible, and you certainly DO NOT want any inductance (coil of wire) in that lead. A water faucet *should* be a good ground, but is not guaranteed - and if you need to use a long wire to connect to it, it will no longer be a good ground. A 6 - 8 foot pipe or rod pounded into the ground within 6 feet of your radio would probably be a good solution. The deeper the better. The physical ground connects to the circuit 'ground'.

Your antenna sounds reasonable, you just need a long wire up in the air that isn't shorted to anything else. Connect the antenna to wire #2 for a first try. You can also try #1 or #? and see what works the best. (It's unclear if the loopstick wire 4 is the very bottom or the first tap. The very bottom is the wire that should go to ground, and the antenna can be tried on the first tap up from the bottom.)

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