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Odd signals and other unusual patterns

Posted: Fri Oct 20, 2017 6:24 pm
by elroy
I've been using my RSP2 with SDRUno for a while now, and have run across a few odd patterns in the frequency display. Some I strongly suspect are actual signals of certain kinds of transmissions I'm not familiar with. Others I think are probably something going on inside SDRplay itself.

I'll look around for examples of these that I want to ask about. Here are two for starters.

1) Yesterday I tuned from 30 to 85 MHz just to see what might pop up in that range, which I've never previously explored. This was with RSP2 attached to a discone antenna, with SDRUno. I basically just worked my way across this spectrum in intervals of about 1.5 MHz, which seemed to be the zoom limit of the frequency display.

While tuning, I noticed a quasi-signal that kept appearing in the center of the display (right above the two o's in the word "Zoom" on SDRUno's main window). I tried AM, FM, CW, USB/LSB, and couldn't make it out to be an actual signal. The fact that it appears dead in the center of every frequency segment I was tuning across was suspicious. It only seems to appear in certain frequency ranges -- I haven't seen it, for example, at HF or at higher VHF/UHF. Is this something going on inside the SDRplay? If so, is there an explanation for it? See screen print:

Image

2) While tuning across HF with a longwire antenna, I've sometimes come across signals that appear to be real station that transmit "cascading" signals -- moving from high to low across a range of frequencies. Below is one that I found on 4.550 MHz. What are these?

Image

(The cascading effect would be more obvious in a video clip -- are these ok to post?)

Re: Odd signals and other unusual patterns

Posted: Fri Oct 20, 2017 9:38 pm
by sdrplay
That is the DC offset. The offset compensation loop reduces it but you can remove it further by adjusting the gain value.

Just make sure your VFO is away from the LO frequency and you'll be fine.

Best regards,

SDRplay Support

Re: Odd signals and other unusual patterns

Posted: Sat Oct 21, 2017 12:44 am
by elroy
Thanks very much for the explanation of the DC offset.

Is the other image posted above (of the "cascading frequency" station) a signal type that people commonly run into?

Also, in the image below there are two "humps" of background noise on the left and right sides of the frequency range, 400 kHz above and below the LO. Is this something internal to the SDRplay?

Image

Re: Odd signals and other unusual patterns

Posted: Sat Oct 21, 2017 12:55 am
by elroy
Here's another odd pattern. Basically spikes all up and down the tuning range, all dancing up and down in unison. As I tune across them I think I can faintly hear what sounds like commercial broadcasting.

Is this a commonly seen manifestation of commercial AM interference?

Image

Re: Odd signals and other unusual patterns

Posted: Sat Oct 21, 2017 2:45 am
by mark.
Yes, I have run across those "cascading frequency" stations on SDR and regular receivers.

Re: Odd signals and other unusual patterns

Posted: Sat Oct 21, 2017 3:17 am
by elroy
Mark (or others), is there any information (or perhaps speculation) on what these "cascading frequency" stations are?

Re: Odd signals and other unusual patterns

Posted: Sat Oct 21, 2017 8:43 am
by DanubeBCL
Do a search on the term "CODAR".
https://www.sigidwiki.com/wiki/CODAR
https://www.youtube.com/watch?v=8OF-yhrtqKo
I cannot explain your patterns on both sides of 10 MHz. I have never seen them.
Your "spikes" look pretty much like computer and/or monitor noise. Try to touch your screen with your palm: Do they increase?
73, Heinrich

Re: Odd signals and other unusual patterns

Posted: Sat Oct 21, 2017 11:47 am
by g1hbe
That pattern of spikes looks like the type of buzz I get from a nearby plasma TV. If you listen in AM you may hear a sharp buzzing sound.

Re: Odd signals and other unusual patterns

Posted: Sat Oct 21, 2017 8:09 pm
by elroy
DanubeBCL wrote:Do a search on the term "CODAR".

Yes, that definitely looks like what it is. It also appears that radars of this type are in use in my area. Thanks for the help!

Re: Odd signals and other unusual patterns

Posted: Sat Oct 21, 2017 8:11 pm
by elroy
g1hbe wrote:That pattern of spikes looks like the type of buzz I get from a nearby plasma TV. If you listen in AM you may hear a sharp buzzing sound.

Hmm, a large plasma TV was probably in use about 25 feet/7 meters away at the time. I'll have to conduct further tests with the TV on and off. Thanks for the help.