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Lot's Going On

Posted: Tue May 07, 2019 10:39 pm
by hfaero
Attached to this post is a screenshot of a waterfall display taken using GRQX running on Linux Ubuntu 18.04 and using my RSP2 receiver. I'm posting this in hope of finding out from more learned colleagues what might be happening with some signals or the receiver that seem to be causing break through from other shortwave bands.

The screenshot shows a 10 hour display of activity in the 8MHz airband from approximately midnight through to 9am local time here in New Zealand.

Those items labelled with a 1 (figures one) appear to be AM radio stations breaking through from other bands. I have an AM bandstop filter on the antenna port (A in case you are wondering) so I know reasonably well that these are shortwave signals and not local AM radio stations but nevertheless despite reducing gain all the way, both IF gain and LNA gain, these signals are persistent at key points of the day. Greyline for instance I get breakthrough on most of my bands of interest, 5MH, 6MHz, 8MHz and 13MHz aero bands and the signal strengths are pretty high and when trying to monitor DX under these it becomes a rather useless pass time! Overnight isn't much better as can be seen. I find it interesting that these out of bands signals don't just fade in and out but they appear to be there from the time they start transmitting as can be seen by the same signals labelled 1 at about 1230Z and 8.895MHz. It seems this signal starts transmitting at 1230Z and stops 30 minutes later and resumes at 1400Z for a further 30 minutes indicating a shortwave scheduled transmission.

The question I have on the above anomaly is: Is this normal behaviour for an RSP2? Should I be seeing out of bands signals even if I reduce the gain levels (or rather attenuate the input)? Is my antenna too big? BTW the antenna is a 40 meter long delta loop terminated with a 9:1 un/un at the apex (triangle shape).

The second thing about this is the chirp sounders or ionosondes at point 2 (figures two). Why the short break at about 8.910MHz. I may be wrong but it looks like every chirp sounder has this small portion blanked out. I think there's scope later to widen the bandwidth and have a look across a couple of MHz as I though chirp sounders swept the entire HF frequency range.

Anyway I find this type of analysis very interesting and a very useful tool in discovering my spectrum. Thanks in advance for any comments or further analysis.
gqrx_wf_8MHz_Overnight.jpg
gqrx_wf_8MHz_Overnight.jpg (345.17 KiB) Viewed 1151 times