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Re: LF: Strong signal on 137 kHz

To: [email protected]
Subject: Re: LF: Strong signal on 137 kHz
From: John Rabson <[email protected]>
Date: Fri, 25 Apr 2014 19:54:13 +0200
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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 
  • 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. 
73 John  F5VLF

On 6 Apr 2014, at 21:31CEST, DK7FC <[email protected]> wrote:


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.

So maybe the problem is on your side. I remember a similar effect by MF WSPR decodes by a EA station. From 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?

73, Stefan/DK7FC

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.

73, Stefan/DK7FC

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’m still suffering from severe QRM.  I was unable to identify it, but there were traces of 50 Hz side bands about -20 dBc.

This was the first signal I had received for some weeks. I’m still hunting the source of interference.

John F5VLF

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