Re: LF: Strong signal on 137 kHz

[John Rabson <john.rabson07@gmail.com>]

Stefan,

On previous occasions when I have noticed side bands on your transmission, they 
have been at worst -40 dBc which is why I was puzzled about the -20. It did not 
make sense. You will note I did not originally suggest whose side bands they 
were as I was not able to identify the transmission.

I have been doing some further checking here and the matter seems to be 
complicated by a lot of strong signals with 50 and 100 spacing across the band. 
Thank you for the suggestion about galvanic coupling. If the weather is fine 
tomorrow I will check the joints in the loop antenna I use for reception.

73,
John  F5VLF

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

> John,
> 
> 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

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