Troubleshooting Crystal Radio: Tips for Building and Improving Reception

[darth boozer]

PVC pipe is fine, but cardboard tubes are often used because they are cheap or free. Sanding the wire insulation is OK, but make sure that adjacent turns cannot short to each other. Because you are not using a capacitor with the coil to form a tuned circuit, you are relying on unknown, stray, capacitance so the signals you pick up could possibly be in the lower part of the HF bands and be subject to fading, or the stray capacitance is changing as you move your arms etc. and thus tuning away from the station. The usual recommended circuit will tune to the AM band and your local stations should be strong and steady as well as being recognisable.

 

[davenn]

I have another question on the diode. In reading up on diode technology, I see it is directional. Does this apply to the crystal radio? The right side of the coil is connected directly to the diode.

View attachment 238993

I'm not sure if it really makes a difference, some one else may comment...
Normally it would go in the other direction as in my post on page 1 of this thread. That is the black bar on the diode should be towards the earpiece

The usual recommended circuit will tune to the AM band and your local stations should be strong and steady as well as being recognisable.

yes agreed, as per the circuit and comments I posted n page 1 of the thread

Dave

 

[Tom.G]

I'm not sure if it really makes a difference, some one else may comment...

Nope, no difference at all.

 

[darth boozer]

A little more reading about the subject could be helpful.
https://www.electronics-notes.com/articles/radio/modulation/amplitude-modulation-am.php
https://www.electronics-notes.com/a...tude-modulation-am-demodulation-detection.php

 

[Mark Palmer]

Thanks again, all.

Another question related to tuning.

The slider or wiper bar is apparently a crude tuning method. I think I will modify this build to install a tuning capacitor. I have this one rated at 365 pF, intended for crystal radio use. It has two solder terminals on each side.The wiring diagram posted early in the thread shows the capacitor connected to both sides of the coil. How exactly should I connect to the terminals?

 

[darth boozer]

The grounded side of the coil should connect to the metal body of the capacitor and the antenna side to the side terminals which connect to the fixed plates (the bottom ones in your picture). At the frequencies involved, a few inches of wire to make the connections will be fine. As a temporary measure for testing, the connections could be made with alligator clips.