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From: John Rabson <john.rabson07@gmail.com>
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Date: Fri, 25 Apr 2014 19:54:13 +0200
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Subject: Re: LF: Strong signal on 137 kHz
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Stephan and LF,

Thank you for your patience everyone. I have at last managed to repair =
my loop antenna satisfactorily and check it out. There appears now to be =
more than one problem in the receiving system:

There are several spurious signals across the LF band
The power supply to the Lowe HF250 receiver now has about 2V peak to =
peak of 50 Hz ripple on its output=20
The Arga display shows a strong additional signal at twice the audio =
frequency output (setting things up for 800 Hz output, I also get a =
noticeable trace at 1600 Hz)
There is a weak output on about 670 Hz even with the antenna =
disconnected

Oh well, out with the oscilloscope and the soldering iron.=20
73 John  F5VLF

On 6 Apr 2014, at 21:31CEST, DK7FC <73dk7fc@googlemail.com> wrote:

> John,
>=20
> Last night i've checked my 50 Hz sidebands (actually 100 Hz) on LF by =
using SpecLab and a Tecsun PL660 receiver, both running on batteries =
(ferrite antenna) and coupled via a cable.
> The sidebands are at -40 dBc, see attachment.
>=20
> So maybe the problem is on your side. I remember a similar effect by =
MF WSPR decodes by a EA station. =46rom that station i'm often getting 2 =
decodes in the same time slot, beeing 100 Hz distant and just 10 dB or =
so in SNR difference, which is also not caused on my side...
> Maybe a galvanic coupling with some mains harmonic currents on the =
antenna cable?
>=20
> 73, Stefan/DK7FC
>=20
>=20
> Am 30.03.2014 23:25, schrieb DK7FC:
>> [...]
>> I can't explain the -20 dBc sidebands. I've measured my sidebands to =
be -35 dBc some time ago and didn't change anything on the LF setup. =
I'll check it soon again.
>>=20
>> 73, Stefan/DK7FC
>>  =20
>>=20
>>=20
>> Am 30.03.2014 13:00, schrieb John Rabson:
>>> This morning at about 0745Z I received a signal which seemed to be =
QRSS. It would have been a strong signal except that I=92m still =
suffering from severe QRM.  I was unable to identify it, but there were =
traces of 50 Hz side bands about -20 dBc.
>>>=20
>>> This was the first signal I had received for some weeks. I=92m still =
hunting the source of interference.
>>>=20
>>> 73
>>> John F5VLF
>>>  =20
> <-40dBc.png>


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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html =
charset=3Dwindows-1252"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: =
after-white-space;">Stephan and LF,<div><br></div><div>Thank you for =
your patience everyone. I have at last managed to repair my loop antenna =
satisfactorily and check it out. There appears now to be more than one =
problem in the receiving system:</div><div><br></div><div><ul =
class=3D"MailOutline"><li>There are several spurious signals across the =
LF band</li><li>The power supply to the Lowe HF250 receiver now has =
about 2V peak to peak of 50 Hz ripple on its output&nbsp;</li><li>The =
Arga display shows a strong additional signal at twice the audio =
frequency output (setting things up for 800 Hz output, I also get a =
noticeable trace at 1600 Hz)</li><li>There is a weak output on about 670 =
Hz even with the antenna =
disconnected</li></ul><div><br></div></div><div>Oh well, out with the =
oscilloscope and the soldering iron.&nbsp;</div><div>73 John =
&nbsp;F5VLF</div><div><br></div><div>On 6 Apr 2014, at 21:31CEST, DK7FC =
&lt;<a =
href=3D"mailto:73dk7fc@googlemail.com">73dk7fc@googlemail.com</a>&gt; =
wrote:<br><br><blockquote type=3D"cite">John,<br><br>Last night i've =
checked my 50 Hz sidebands (actually 100 Hz) on LF by using SpecLab and =
a Tecsun PL660 receiver, both running on batteries (ferrite antenna) and =
coupled via a cable.<br>The sidebands are at -40 dBc, see =
attachment.<br><br>So maybe the problem is on your side. I remember a =
similar effect by MF WSPR decodes by a EA station. =46rom that station =
i'm often getting 2 decodes in the same time slot, beeing 100 Hz distant =
and just 10 dB or so in&nbsp;SNR difference, which is also not caused on =
my side...<br>Maybe a galvanic coupling with some mains harmonic =
currents on the antenna cable?<br><br>73, Stefan/DK7FC<br><br><br>Am =
30.03.2014 23:25, schrieb DK7FC:<br><blockquote type=3D"cite">[...]<br>I =
can't explain the -20 dBc sidebands. I've measured my sidebands to be =
-35 dBc some time ago and didn't change anything on the LF setup. I'll =
check it soon again.<br><br>73, =
Stefan/DK7FC<br>&nbsp;&nbsp;<br><br><br>Am 30.03.2014 13:00, schrieb =
John Rabson:<br><blockquote type=3D"cite">This morning at about 0745Z I =
received a signal which seemed to be QRSS. It would have been a strong =
signal except that I=92m still suffering from severe QRM. &nbsp;I was =
unable to identify it, but there were traces of&nbsp;50 Hz side bands =
about -20 dBc.<br><br>This was the first signal I had received for some =
weeks. I=92m still hunting the source of interference.<br><br>73<br>John =
F5VLF<br>&nbsp;&nbsp;<br></blockquote></blockquote><span>&lt;-40dBc.png&gt=
;</span><br></blockquote><br></div></body></html>=

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