Equipped with rubber gloves and rubber boots and dark goggles, , connect
"earth" of the power supply to your door frame..???
Maybe measure DC PD first but not such sense of adventure.
G3GVB
----- Original Message -----
From: "Laurence KL1X" <[email protected]>
To: "Laurence KL1X" <[email protected]>
Sent: 22 August 2006 05:38
Subject: LF: These sliding doors again
Considering the extenuative affects to kill common mode qrm coming from
inside the room, up the coax and out Ive been playing to try to find out
whats what. Yep an Im using isolating toroids and all that guff.
Here we go
For a merit test I "built" my own 4 x 3 metre flexible doorway in an area
similar but without the metal frame being there. This was with one
continuous length of folded aluminum foil some 4 cms in width and a couple
of thicknesses to give it some mechanical strength with all that tugging -
and some 14 metres in circumference.
I compared the extenuative results of common in building noise with the one
with a known killer of QRN my favorite sliding balcony door frame - At 137
Khz the door frame gave appx 30-40dB of noize attenuation (nice) my aluminum
made up version standalone 4dB... or less. Open circuiting the aluminium
made up little difference
So I pondered - I knew from testing in Singapore that the metal frame in my
hotel that worked so well wasn't connected to "mains" earth - but what about
this one here in Shanghai? - Measured it and hey presto it is, and low Z
too, certainly less than 1 ohm - theyve added a Earth safety strap
somewhere and all the buildings doorways and sliding doors on the balconies
are all boded together at "building earth" (notice Im not saying radio)
potential and defacto we have a screened box - with my eprobe poking out of
one side and the screen connected to that box.
So this left the question of what was happening in Singapore? - Ive found
out that the sliding door frame is connected to the steel work of the
building but for some reason there is No connection to the mains earth in
the 220vac supply - I actually think this is a bit dodgy but heck that mains
earth was hot with RF and brought the noise up by 30dB, here luckily in
Shanghai it doesn't.
Choosing the right balcony sliding door for your probe has merits - the one
on the North side cuts the noize out but then I get pylon hash, the one on
the southside is much quieter but now screened from Asia/Americas and Eu -
but I can still see DCF39
So no tuned loops, tooned earths, counterpoises or what ever just a screened
metal box that keeps the rubbish mostly inside. Mostly. As Ive seen before
if I was on the top floor its works pretty well for rx if i can get my probe
above the roof line but Im on floor 3 out of 12 and by pushing the probe
out further and further away from the building makes a huge difference -
more than 1 S point per metre at 200Khz on some of the local NDB's.
I have a cunning plan (as one famous actor said once "so cunning if you put
a tail on it, you would call it a fox"), to get some form of earth into the
ground and extend is camouflaged up the side of the building. If it works it
will be interesting to see what if any affect is has on the qrm, if it
doesn't Ill probably be in jail.
Laurence, KL1X in BY, enroute tomorrow to KL7
From: [email protected]: [email protected]:
Fri, 18 Aug 2006 14:33:59 -0800Subject: LF: condx
DCF39 seen here from 1809z till 2143z - signals were coming and going and
below audible - The signal here was seen some 24mins before sundown at
Magdeburg and lost at my dawn. Theres hope! Laurence PM01 ShanghaiMini whip
on a 7m fishing pole shoved out horizontally off a 3rd floor screened
balcony
Express yourself instantly with Windows Live Messenger! Windows Live
Messenger!
_________________________________________________________________
Express yourself with gadgets on Windows Live Spaces
http://discoverspaces.live.com?source=hmtag1&loc=us
|
