UnFETtered Crystal Radio

[imweso]

I did a search for the "UnFETtered Crystal Radio" and could find no posts.

The UnFETtered Crystal Radio is a project in rf circuits. 

I was just wondering if any other JFETS have been tried in the circuit.  I tried an MPF102
with no luck.  It is a part from Radio Shack.  I guess it could be bad.  I replaced it with a diode and the circuit works.  I can't believe there is that much difference beweeen JFET types.  The circuit calls for a 2N5484.

Thanks

IMWESO

 

[Hero999]

You mean the project linked below?
http://www.electronics-lab.com/projects/rf/011/index.html

I wasted my time reading the whole thing and it provided no explanation of how it actually works. The author says it doesn't use diode rectification which I how I would thing it would work.

He also made an incorrect statement:
"Devices that are static sensitive have protection diodes on the inputs, and the ALD device certainly has those. Basic JFETs also have a protective diode between the gate and source connections, presumably for the same reason, but neither the QST design, nor my adaptation of it, use any internal diodes as a rectifier. "

JFETs don't contain any protective diodes, there's a parasitic diode between the gate and source but that's nothing to do with static protection and is an inherent part of the JFET. JFETs are also less sensitive to static than MOSFETs because they don't have a thin metal oxide layer which can easily be damaged by high voltage spikes.

I wouldn't be surprised if there are other errors made by the author such as his claim that it doesn't use the JFET's internal diode.

Have you tried using a germanium or Schottky diode?

 

[imweso]

I did try a diode and the circuit works.  I just thought it would be nice if I could use a cheap transformer and an ear bud phone.

The author has this to say about the use of a JFET as a detector----

"According to the experts on the net, much success has been enjoyed by one and all, and there's a lot of chatter about this most recent innovation in the realm of simple AM receivers.  (292 posts so far, to the 'Rap'n'tap' chatroom of the American Crystal Set Society alone.)

I can't find any of these posts.  It sounds like other folks have made this work.  I have a lot of time so I guess I will try to chase down some more info.

Thanks HERO,

IMWESO

 

[Hero999]

Have you tried using a diode with the transformer and ear bud?

I see no reason why it shouldn't work.

For more volume use a voltage doubler circuit.