Message-ID: <5070C574.4030005@iup.uni-heidelberg.de>
Date: Sun, 07 Oct 2012 01:57:40 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org
Subject: LF: GRRRRR!! Now i know...
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Oh now, i can't belive it. Must tell you that:

All the years i suffered from QRM which seemed to come from DLF at 153 
kHz. Now as i installed the new wideband LF/MF probe i got even more 
QRM. The design is not so far from the PA0RDT design. After increasing 
the antenna by another meter on the top of the roof i got worse signals 
than before.

Yesterday i found that it must be a resonance on the cable since i could 
reduce the effect dramatically by adding a 1 nF C and a 1 kOhm R on the 
RX end.
But i still saw IM. This was the problem with all my previous antennas. 
The signals levels are close to the noise floor but when i increased the 
probe C it became worse....

Now i checked this oscillation on an oscilloscope. By adding some C or R 
i could reduce the amplitude of the signal but never the frequency, 
which is strange. Then i noticed that it is AM !!!!! So it must be a 
transmitter very close to me since the signal levels were 4V pp here, 
and this started to cause noticable IM on LF and MF.

I checked the web with some keywords like "radio" and "heidelberg" and 
quickly found this

It is AFN in Heidelberg on *1143 kHz*. This is a *AM transmitter running 
1 kW in about 1 km distance!*
http://www.asamnet.de/~bienerhj/1143-HD.html#1143-HD
It is a 100m tower. I never noticed it since i live here, odd.
Here one can read that AFN Heidelberg will be QRT on MF very soon: 
http://www.afneurope.net/Home/ArticleDisplayDD/tabid/649/Default.aspx?aid=25644

So now, that may explain why my RX site often suffered from QRM. And 
that explains why a resonated circuit in front of the first active 
device in my E field antennas were always the best solution for me!

I don't want to wait until they go QRT but i'm looking forward to see 
the difference in the noise background when they go off. For now i need 
some kind of filter and i have to take care that the input of the first 
JFET does not become overloaded.

Will go on investigating!...

73, Stefan/DK7FC

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Oh now, i can't belive it. Must tell you that:<br>
<br>
All the years i suffered from QRM which seemed to come from DLF at 153
kHz. Now as i installed the new wideband LF/MF probe i got even more
QRM. The design is not so far from the PA0RDT design. After increasing
the antenna by another meter on the top of the roof i got worse signals
than before. <br>
<br>
Yesterday i found that it must be a resonance on the cable since i
could reduce the effect dramatically by adding a 1 nF C and a 1 kOhm R
on the RX end.<br>
But i still saw IM. This was the problem with all my previous antennas.
The signals levels are close to the noise floor but when i increased
the probe C it became worse....<br>
<br>
Now i checked this oscillation on an oscilloscope. By adding some C or
R i could reduce the amplitude of the signal but never the frequency,
which is strange. Then i noticed that it is AM !!!!! So it must be a
transmitter very close to me since the signal levels were 4V pp here,
and this started to cause noticable IM on LF and MF.<br>
<br>
I checked the web with some keywords like "radio" and "heidelberg" and
quickly found this<br>
<br>
It is AFN in Heidelberg on <b>1143 kHz</b>. This is a <b>AM
transmitter running 1 kW in about 1 km distance!</b><br>
<a class="moz-txt-link-freetext" href="http://www.asamnet.de/~bienerhj/1143-HD.html#1143-HD">http://www.asamnet.de/~bienerhj/1143-HD.html#1143-HD</a><br>
It is a 100m tower. I never noticed it since i live here, odd.<br>
Here one can read that AFN Heidelberg will be QRT on MF very soon:
<a class="moz-txt-link-freetext" href="http://www.afneurope.net/Home/ArticleDisplayDD/tabid/649/Default.aspx?aid=25644">http://www.afneurope.net/Home/ArticleDisplayDD/tabid/649/Default.aspx?aid=25644</a><br>
<br>
So now, that may explain why my RX site often suffered from QRM. And
that explains why a resonated circuit in front of the first active
device in my E field antennas were always the best solution for me!<br>
<br>
I don't want to wait until they go QRT but i'm looking forward to see
the difference in the noise background when they go off. For now i need
some kind of filter and i have to take care that the input of the first
JFET does not become overloaded.<br>
<br>
Will go on investigating!...<br>
<br>
73, Stefan/DK7FC<br>
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