Re: Weird "signal diagnostics" readings

Kenneth Sejkora

I can attest to this 'phenomenon'.  I use an RTL-SDR V3 dongle with SDRSharp in direct sampling mode to listen to 20-meters and other frequencies in the HF band.  I live between Boston and Providence, so there are plenty of AM transmitters in the vicinity.  After about 18:00 local time, and up until about 07:00 local, the spectrum displays some minor phantom signals about every 60 kHz apart.  However, during daylight hours, there are strong signals every 10.0 kHz apart on exactly 10-kHz multiples... 14,100.0, 14,110.0, 14,120,0, etc., several of which exhibit audible audio intermodulation with bandwidths up to 4 khz wide, like listening to a AM broadcast..  Same thing if I drop down to 75-meters... 3,800.0, 3810.0, 3820.0, etc.  No, I do not have any kind of AM broadcast high-pass or band-stop filter installed.  But once it starts getting dark, somewhere between about 17:30 and 18:30 local, those 10.0-kHz interval signals disappear.  I suspect it's a combination of both higher daytime power and different antenna patterns, as almost all of the AM broadcasters in the area exercise both practices of diurnal/nocturnal power and antenna patterns changes.

I did consider the possibility of temperature-related phenomena, such as joints/junctions in wires, fences, rain gutters, etc. being heated up by the sun and forming a pseudo-diode junction that radiated RF, but with recent single-digit daytime temps, the pattern looks the same as it does on warmer days.

Of course, your mileage may vary depending on the number of AM BCB stations, transmit power, frequencies, antenna patterns, etc. in your local vicinity.  I've been considering buying and trying an AM band-stop filter to see if it helps.  I'd welcome any experiences, successes, or failures anyone has had with such band-stop filters.

Good luck!

Ken, WBØOCV Norton, MA USA
41.959546N, 71.163996W  FN41kx

On Wednesday, January 23, 2019, 08:05:28 AM EST, jdow <jdow@...> wrote:

Dumb question - what time of day was this and what time of day do you usually
use it? At least in the states most broadcast stations run with different day
and night power and antenna patterns. And noise and signals do show a daily
pattern even on LF, at least around here in the past.


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