[sdiy] sniffing

[Grant Richter]

>From the RF standpoint, you can only take an unbalanced reading relative to
actual earth ground.

Meaning a true earth ground. US code specifies a #8 wire run (4-5 mm) to a 8
foot long ground rod, then tested and adjusted with salt to a ground
resistance of less than 20 milli-ohms. That is for a common home electric.

Any inductance in series to earth ground will reduce the differential
voltage.

Running through buildings could account for a lot of added inductance, so
like for a shortwave radio, you should run your own ground lead to the
building ground stake.

And an attic long wire would make a good large scale detector. Just hook
your electrometer up in place of a short wave.

> From: "Czech Martin" <Martin.Czech at Micronas.com>
> Date: Thu, 24 Apr 2003 15:11:26 +0200
> To: "Grant Richter" <grichter at asapnet.net>, "jhaible" <jhaible at debitel.net>,
> "Magnus Danielson" <cfmd at swipnet.se>
> Cc: <synth-diy at dropmix.xs4all.nl>
> Subject: RE: [sdiy] sniffing
> 
> I bought a styro foam ball (will cover with alu foil) for E-field
> and a toroid (some copper windings on it and alu foil
> E-field shielding) for B-field (H-field).
> Some early experiments show n x 10mV of AC line noise (50 Hz
> fundamental, but much overtones) for the E-field (or
> voltage, as J.H. pointed out) probe.
> I try to build a jfet decoupling amp for the E-field
> sensor, the other one will go into 50 Ohm scope input.
> 
> Interesting side effect: I tryed to put the scope ground clamp/tip
> loop into a metal case in order to see the shielding effect...
> I found out that the 107 MHz FM stuff will disappear if the loop
> is far away from metal (table etc.). So I think that some capacitanc
> is needed in order to tune the loop for this frequency.
> Since I could'nt close the metal case completely, no shielding
> was observed....
> 
> btw.: I learned that the Hameg 1505 scope has no 50 Ohm
> termination as built in switch (which I thought it had,
> bacause all the Tek scopes have it and I'm used to it).
> So a clear reflection could be seen when using RG58
> 50 Ohm lines and a square wave generator.
> You have to buy a special through-termination-resistor-BNC-thing
> for a ridiculous price.
> I then opted for a BNC-T and a BNC-50-Ohm termination piece,
> that is ok, at 1/10 of the cost.
> 
> m.c.
> 
> -----Original Message-----
> From: Grant Richter [mailto:grichter at asapnet.net]
> Sent: Dienstag, 15. April 2003 19:22
> To: jhaible; Czech Martin; Magnus Danielson
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] sniffing
> 
> 
> If this appeals to you, you would probably enjoy this book:
> 
> "Listen to Radio Energy, Light and Sound"
> 
> by Calvin R. Graf
> Howard W. Sams publisher 1978
> ISBN 0-672-21525-X
> 
> Describes a simple audio amplifier with simple detector heads for
> microwaves, earth fields, lots of stuff, including a shorted input
> transducer for Barkhausen noise (discontinuous movements of mobile magnetic
> boundaries between magnetic domains).
> 
> A great amateur scientist book, shows you how to use stuff you already know
> in ways you might not have thought of.
> 
> Amazon.com shows it out of print:
> 
> http://www.amazon.com/exec/obidos/tg/detail/-/067221525X/qid=1050427058/sr=1
> -4/ref=sr_1_4/002-1699855-4018446?v=glance&s=books
> 
> but worth looking for.
> 
> 
>