"FM Snake" Project


Tommy Gober
 

I recently came across this article about building an FM broadcast RF sniffer called an "FM Snake". It's not QRP related, per se, but still an interesting simple little circuit for playing around with if you live near an FM broadcast facility.


Tommy, N5DUX


Tom Sevart
 

On 10/03/17 15:51, Tommy Gober tommy@neodux.com [4sqrp] wrote:


I recently came across this article about building an FM broadcast RF
sniffer called an "FM Snake". It's not QRP related, per se, but still an
interesting simple little circuit for playing around with if you live
near an FM broadcast facility.

http://www.ericbrasseur.org/electrosmog_snake.html

Tommy, N5DUX
Interesting. I don't know why the design has two wires below the diodes since they're wired together in parallel. I'd think just one wire below the diodes would be sufficient, since that part is basically acting as an antenna.


--
Tom Sevart N2UHC
St. Paul, KS


cornhusker
 

They are different lengths to take in consideration the variance in wavelength from the top to the bottom of the FM broadcast band..it is 20 MHz wide.    :)

73 de K0NEB

On ‎Wednesday‎, ‎October‎ ‎04‎, ‎2017‎ ‎06‎:‎40‎:‎12‎ ‎PM, Tom Sevart tmsevart@... [4sqrp] <4sqrp@...> wrote:


 

On 10/03/17 15:51, Tommy Gober tommy@... [4sqrp] wrote:
>
>
> I recently came across this article about building an FM broadcast RF
> sniffer called an "FM Snake". It's not QRP related, per se, but still an
> interesting simple little circuit for playing around with if you live
> near an FM broadcast facility.
>
> http://www.ericbrasseur.org/electrosmog_snake.html
>
> Tommy, N5DUX

Interesting. I don't know why the design has two wires below the diodes
since they're wired together in parallel. I'd think just one wire below
the diodes would be sufficient, since that part is basically acting as
an antenna.

--
Tom Sevart N2UHC
St. Paul, KS

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Tom Sevart
 

On 10/04/17 19:19, Joe E cornhusker@yahoo.com [4sqrp] wrote:


They are different lengths to take in consideration the variance in
wavelength from the top to the bottom of the FM broadcast band..it is 20
MHz wide. :)
No, the wires below the diodes are the same length. From the text: "The wires below the two diodes should be about 122.5 centimeters long (48¼"). " I say you don't need two wires when they're both connected at the same point, but having two different length wires might work sort of like a fan dipole works, but with something like this as a near field receiver I don't think it's that critical.

--
Tom Sevart N2UHC
St. Paul, KS


Jim Sheldon
 

Read it a bit closer Tom. He says you could use a single wire below the diodes but he made the whole thing from zipcord and rather than waste the wire he used it.

W0EB

On Oct 4, 2017, at 8:34 PM, Tom Sevart tmsevart@gmail.com [4sqrp] <4sqrp@yahoogroups.com> wrote:

On 10/04/17 19:19, Joe E cornhusker@yahoo.com [4sqrp] wrote:


They are different lengths to take in consideration the variance in
wavelength from the top to the bottom of the FM broadcast band..it is 20
MHz wide. :)
No, the wires below the diodes are the same length. From the text:
"The wires below the two diodes should be about 122.5 centimeters long
(48¼"). " I say you don't need two wires when they're both connected at
the same point, but having two different length wires might work sort of
like a fan dipole works, but with something like this as a near field
receiver I don't think it's that critical.

--
Tom Sevart N2UHC
St. Paul, KS

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Posted by: Tom Sevart <tmsevart@gmail.com>
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Sam Neal
 

Hello,

The FM snake is a very basic crystal radio using a Light Emitting Diode as the
detector. No audio could be heard if headphones ( high impedance! ) were used
as the mode being detected is FM, where there is no amplitude variation on
it's carrier. Basically, someone " re-discovered " the crystal radio from 1905
or so.

In my Technician classes, I use exactly the same circuit, with a 2 meter
mobile for my RF source. but with wires resonant in the 2 meter band to
demonstrate the pattern of simple 4 element 2 meter Yagis.

Sam Neal N5AF
___________________________________________________________________

------ Original Message ------
Received: Tue, 03 Oct 2017 08:22:29 PM CDT
From: "Tommy Gober tommy@neodux.com [4sqrp]" <4sqrp@yahoogroups.com>
To: "qrp-l@mailman.qth.net" <qrp-l@mailman.qth.net>, 4sqrp@yahoogroups.com
Subject: [4sqrp] "FM Snake" Project

I recently came across this article about building an FM broadcast RF
sniffer called an "FM Snake". It's not QRP related, per se, but still an
interesting simple little circuit for playing around with if you live near
an FM broadcast facility.

http://www.ericbrasseur.org/electrosmog_snake.html

Tommy, N5DUX