[sdiy] 100 MHz EMI, what can it be?

[Czech Martin]

Yes, Faraday cages... I still wonder if this RF soup together
with 50/60/16 2/3 Hz power line dirt is really good for peoples health.
I'm not over suspicious, but the situation is only since 40 years
or so, and growing, so long term effects could still be hidden.

A friend of mine built a new house and asked me what to do in his studio.
I proposed a faraday cage, aluminum or copper foil, etc.
He did not understand and did nothing...
I think the extra cost would have beend so low, that you can not
express it in % of the total building cost.


m.c.

-----Original Message-----
From: greg montalbano [mailto:greg.montalbano at ucop.edu]
Sent: Montag, 14. April 2003 19:46
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] 100 MHz EMI, what can it be?


Railroad communications, cordless phones, baby monitors, car phones, FM & 
AM stations, police & emergency broadcasts -- these days, the soup is so 
thick I'm surprised we don't ALL live in Faraday cages.

I live in the San Francisco bay area -- VERY heavy radio saturation, with 
many hills & tall buildings to create standing-wave pockets.  I, too, have 
had the experience of trouble-shooting a noisy circuit, only to find that 
if I moved it to another part of my studio, the noise vanished.

(Back when I used to play bass, I found that the audio "sweet spot" in the 
room corresponded to the phantom radio sweet spot -- moving two feet to the 
right made the interference go away.  When several of us used to get 
together to play, we called the ensuing twisting & 
contorting  "interference tai-chi").

~GMM


At 07:17 PM 4/14/03 +0200, Rene' wrote:
>Hi Martin et al,
>
>Well, I have the Bonn AM Station (WDR2, 720kHz) in close
>proximity, and there are also a couple of FM stations in
>line of sight. If the probe is open, and I touch the tip
>I can see the 720k carrier riding on the 50Hz pickup.
>If I short the probe the 720k is gone, and I can see
>something in the neighborhood of 100MHz too. (Some 200uV)
>Probably pretty normal in FM Station dense countrys like
>Germany.
>
>Which reminds me that I have once built a FM-detector, which
>consisted out of a loop of wire with 10-15 cm diameter, and a
>20pF trim cap. And also a AA118 Ge-Diode for demodulaton of
>the signal. (Use a 2000ohms Headphone, or something suitably
>matched with a transformer.)  In a way this is similar to your
>arrangement, the loop and capacitance of the scope lead probably
>form a tuned circuit as well. Very interesting, I had 3 stations
>trong enough that you actually would hear something, although you
>can't really separate the individual stations (the tuned circuit
>is not haveing enough Q). But still I found that pretty amazing.
>
>Cheers,
>  René
>
>
>Czech Martin wrote:
>>Bingo,
>>107,0MHz or 107,7MHz FM , 500W
>>directly in my neighbourhood.
>>Do you see something like this with your local FM stations?
>>m.c.
>>
>>-----Original Message----- From: René Schmitz
>>[mailto:uzs159 at uni-bonn.de] Sent: Montag, 14. April 2003 12:01 To:
>>Czech Martin Cc: synth-diy at dropmix.xs4all.nl Subject: Re: [sdiy] 100
>>MHz EMI, what can it be?
>>
>>Could that be be a FM radio station? I would check with a receiver
>>what that signal is.
>>Cheers, René
>>Czech Martin wrote:
>>
>>>If I connect the (long) ground clip of the oscilloscope probe to
>>>the tip, I get a nice loop. I can see 10 mVpp, around 100MHz. No
>>>matter how I orientate the loop, it will not disappear.
>>>What can this be? Computer is of, cell phone is much higher, wireless 
>>>phone should also be higher.
>>>Of course, connecting the probe tip to shield via 5mm wire will
>>>make the noise disappear, so it is clearly something from outside
>>>the scope.
>>>I live near a railway track, is this railway communication radio?
>>>m.c.
>
>--
>uzs159 at uni-bonn.de
>http://www.uni-bonn.de/~uzs159
>
>
>
>