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Date: Sun, 15 Dec 2013 17:33:12 +0100
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org, Paul <paul@abelian.netcom.co.uk>
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Subject: Re: LF: A short VLF experiment at DK7FC
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Status: O

Hi Peter, VLF,

Did you see a trace on your grabber? Can you show me a link or a screensh=
ot?
The signal is well visible on Paul Nicholson's excellent VLF grabber,=20
http://abelian.org/vlf/fbins.shtml#p=3D1387116000&b=3D110&s=3Dsp but far =
from=20
stable. Is instability is due to my signal of course. Distance to Paul=20
is 880 km, http://no.nonsense.ee/qth/map.html?qth=3DIO83XQ&from=3Djn49ik0=
0wd

You are right, there are many things to optimise. One thing is the=20
housing of the PA. Now it is just mounted on a wooden plate. It is a H=20
bridge using 4x IRFP460, switching directly at 230V*1.41, so the output=20
of the PA is on mains potential! There is no galvanic decoupling=20
transformer on the output (which would allow to use a grounded coax=20
then) because such a transformer would have to be a VERY big ferrite=20
core with many many turns (> 100). So the PA output is directly=20
connected to the primary winding of the loading coil, which couples its=20
field into the resonance winding (1200 turns). So the feed line is=20
floating on an unknown voltage which depends on the capacitive coupling=20
to sourrounding things. In the field experiments 2010/2011 this was no=20
problem. But now it is. I guess this is causing EMC problems to the /2=20
frequency divider, sometimes. Thus, i will put it into a metallic box=20
which is grounded to earth potential.

Another problem is the parallel capacitor which i have to add to come on=20
resonance. It's capacity is not high enough and i have to add about 10m=20
or wire hanging arround. This additional wire is moving in the wind=20
blasts and causes further instability of the signal (kind of AM due to=20
modulated resonance peak, i.e. antenna current). Another way would be to=20
add more turns to the coil but this antenna system  is voltage limited=20
and it doesn't matter at all if i have to put 400W or 500W into the syste=
m.

BTW this night/day it was 850 mA antenna current and about 400W RF=20
power. I will plan to do more QRO, when the new capacitor is ready to use.

Here is an image of the arrangement, taken 30 minutes ago:=20
https://dl.dropboxusercontent.com/u/19882028/VLF/20131215_165406.jpg

As soon as the C of "DK7FC" is finished, i will run some OPDS32=20
sequences for DF6NM and Paul Nicholson and others :-)
BTW i have disconnected my VLF grabber antenna since the RX is=20
overloaded anyway. Now it is easier to identify eventual phase glitches=20
(could be on the RX side as well, though).

73 and thanks for watching.

Stefan/DK7FC


Am 15.12.2013 14:49, schrieb PA1SDB, Peter:
> Stefan,
> Signal is O.K., but stabillity is'nt :-(
> To much spread around center frequency.
>
> (I know.... I'm complaining about 0.01 Hz drift..........)
>
> 73's Peter
>
>
> ----- Original Message ----- From: "Stefan Sch=E4fer"=20
> <Stefan.Schaefer@iup.uni-heidelberg.de>
> To: <rsgb_lf_group@blacksheep.org>; "Paul" <paul@abelian.netcom.co.uk>
> Sent: Sunday, December 15, 2013 4:14 AM
> Subject: Re: LF: A short VLF experiment at DK7FC
>
>
> Since 4:10 UTC, the signal is available without interruptions now on
> 8.97000500 kHz.
>
> 73, Stefan/DK7FC
>
> Am 14.12.2013 20:50, schrieb Stefan Sch=E4fer:
>> Hi all,
>>
>> Tomorrow the rain probability is just 10% and so i think i can risk=20
>> to run a short VLF experiment on 8970.00500 Hz. I'm using the fixed=20
>> antenna at JN49IK00WD. These days, the QRN is very low for quite a=20
>> long time! The plan is to run about 500W RF power, or more, depending=20
>> on the voltage limit of the antenna. And the plan is to start=20
>> transmitting tonite, after the experiment with VO1NA, i.e. i'll come=20
>> on air arround 2 UTC, hopefully. I will run the test until the late=20
>> afternoon. First i'm TXing a stable frequency until 9 UTC, later some=20
>> DFCW-600, and then maybe some tests in OPDS32.
>> Suggestions welcome.
>> BUT it all depends on the WX. If it starts to rain then i have to stop.
>> Will someone give it a try and watch for me?
>>
>> 73, Stefan/DK7FC
>