HF Noise Jump - Wellgood Loop / RX-888 MKII

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Joined: Thu Aug 20, 2020 10:13 am

HF Noise Jump - Wellgood Loop / RX-888 MKII


Unread post by skyking_comms »

I have been testing a Wellgood Loop Antenna with an RX-888 MKII. I've been getting impressive results, especially around 5 MHz for the UK Aero Volmets where there is a low noise floor.

But I have a huge noise jump from around 8.5 MHz to 12 MHz which is active 24/7. I've turned off all electricals in the house, used a linear PSU, moved the loop to different locations in the garden and replaced my cable connectors - but the noise jump is still there. It's annoying at it's in the aero band I'm most interested in.

Wondering if anyone has any ideas on what it could be based on the shape of the noise jump?

For anyone interested in more information on the Wellgood there is a good write up here - http://www.merseyradar.co.uk/m1geo-well ... op-antenna




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Re: HF Noise Jump - Wellgood Loop / RX-888 MKII


Unread post by KA1GJU »

I have an active loop that I use for DF'ing noises (RFI). I plot the nulls on a paper map (google map in satellite map mode zoomed in to the neighborhood) or use APRS.fi and use the plotter tool zoomed in on a satellite map thats zoomed in. Neighbors treadmill and leaky powerlines were found using mine, as well as getting bearings on QRM on lower ham bands.
Use the tools you have to zero in on the noise, the loop antenna!

The second image you posted is of +2MHz of bandscope, if you zoom in you may find that they may be HF BC stations, see my humble 912kHz wide images attached. There are lots of them in that 31m band and 25m band! One really needs to zoom in and look for repeating QRM signals, such as every xx kHz along the spectrum. When looking at 1MHz or more of bandwidth at one time, you miss out on all the nuances hidden inbetween the -30dBm BC stations!
The activity I see in your 2nd screen shot, happens to fall right in those two bands (31 and 25m). If I were a gambling man, I would say you are hearing the HF BC stations!

I just realized you were speaking of the noise floor! Not the strong signals. My bad!
Could it be the result of the band pass filters kicking in or out? I can't seem to locate what the RX-888 has for filters or when they become active or inactive. My SDR-iq has mechanical
filters, while a user is using it on my server, I know when they are making large frequency changes. Ka-chunk... ka-chunk...

73 Kriss KA1GJU
25M HF BC Band activity
25M HF BC Band activity
31M HF BC Band activity
31M HF BC Band activity

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