New user question - please see my screenshot

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StephenT
Posts: 5
Joined: Tue Apr 11, 2017 11:52 pm

New user question - please see my screenshot

Postby StephenT » Thu Apr 13, 2017 6:03 pm

What are these recurring signal peaks? Do i have an incorrect setting?
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g1hbe
Posts: 217
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: New user question - please see my screenshot

Postby g1hbe » Thu Apr 13, 2017 11:13 pm

Looks like you have a strong local source of interference, maybe from a switch-mode psu or a plasma TV. It may even be from your own home/shack. What antenna system are you using?

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Andy

StephenT
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Joined: Tue Apr 11, 2017 11:52 pm

Re: New user question - please see my screenshot

Postby StephenT » Fri Apr 14, 2017 2:21 am

My present antenna is a longwire, end-fed to the high impedence input of the SDR. I plan to make up several 9:1 unun's with different cores (considering 2,6,31,43,52,61) and switch between them depending upon the frequency range I am observing. Probably a bit overkill, but they are inexpensive and easy to make. If someone reading this has already done that with poor results, PLEASE TELL ME and save me some trouble!!

That signal seems to be around 60K or so apart. I also thought about a switching power supply being the culprit and turned off my laptops as well as the CFL bulbs. I DIDN'T turn off the FT990 but if it were making that kind of signal, I would have thought I would have noticed it long ago; I am relatively sure that it is has a switching power supply, however, and will do that check tomorrow.

So far, with such a marginal antenna, I am quite impressed with the SDR2. Might take a couple of lifetimes to figure out all the software settings - still not sure I completely understand decimation, but I'm getting there.

For transmitting, I use a 134 ft. inverted V fed with homebrew open wire feeders and I am using either a Kilowatt Matchbox or a homebrew transmatch. I considered building a duplex switch so as to use the same antenna for the SDR, but not so sure that is a good idea yet.
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DanubeBCL
Posts: 170
Joined: Sat Jul 02, 2016 12:39 pm

Re: New user question - please see my screenshot

Postby DanubeBCL » Fri Apr 14, 2017 6:57 am

Appr. 75 kHz spacing. Could be a switched power supply or plasma/LCD telly, indeed.
If the source is in your own home (room), try a common mode choke in the coaxial cable at the receiver input or better ban every switched PS from your house. When the source is your neighbour: Good luck with your negotiations!
The peak at 7.2 MHz indicates that a resonant ham band antenna (dipole?) is used. Just guessed.
73, Heinrich

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StephenT
Posts: 5
Joined: Tue Apr 11, 2017 11:52 pm

Re: New user question - please see my screenshot

Postby StephenT » Fri Apr 14, 2017 3:53 pm

Further investigation revealed a noise signal of 12db strength being generated either the by the laptop running the software or the SDR itself. See the attached screenshot.

Screenshot (4-50%).gif
Screenshot (4-50%).gif (78.51 KiB) Viewed 1834 times


Looking at the CPU usage at 10MHz and Decimation 1, I think that noise in my receiver is being generated by the laptop. I do have ferrites ordered for the USB cable as well as other connecting cables and see if that helps.

Sniffing for RF with my Startek, the SDR is producing some, the laptop is producing some, the laptop power supply is producing some. Unplugging the SDR didn't reduce the receiver noise, since the laptop is still working away. Stopping the software reduced the noise by 12db. Turning off the laptop (a Dell Inspiron with the Dell switching power supply) dropped the noise level by another 12db and effectively left only band noise as the hash was gone. Interesting, since my Dell Latitude does not seem to be making any noise. I'll post this message and then turn off the Latitude and see what happens and post the results.

Thanks folks for your replies. I appreciate your input and am sure I will be back with more queries!
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StephenT
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Joined: Tue Apr 11, 2017 11:52 pm

Re: New user question - please see my screenshot

Postby StephenT » Fri Apr 14, 2017 4:03 pm

LAPTOP UPDATE: no signal difference on the receiver when turning off the Latitude. The Latitude runs a Core i5 and the Inspiron runs an older Pentium Dual Core. I would assume that is the primary difference in the noise level since the i5 runs with much less power; the power supplies appear identical, even though they are most likely somewhat different in their design.
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g1hbe
Posts: 217
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: New user question - please see my screenshot

Postby g1hbe » Fri Apr 14, 2017 7:41 pm

Stephen - you mention a longwire antenna connected to the Hi-z input. Is this a longwire *directly* into the RX? If so, I'm sure you know that these days bringing a high-impedance wire into your shack is a cast-iron way of picking up every bit of noise in your own house and your neighbours. A coax feed to a transformer-fed longwire would be better.

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Andy

StephenT
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Joined: Tue Apr 11, 2017 11:52 pm

Re: New user question - please see my screenshot

Postby StephenT » Sat Apr 15, 2017 1:30 am

Hey Andy. Yes indeed and unfortunately, the longwire comes directly into the shack and the SDR. HOWEVER, I am going to build some 9:1 ununs and get that wire back outside and bring coax into the shack. I'll order out the toroids next week and experiment with several to see which mixture gives me the best overall performance. I'll post my results in a new topic in case anyone might find it helpful.

73, Steve
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DanubeBCL
Posts: 170
Joined: Sat Jul 02, 2016 12:39 pm

Re: New user question - please see my screenshot

Postby DanubeBCL » Sat Apr 15, 2017 6:25 am

StephenT wrote:the longwire comes directly into the shack and the SDR.
This is no good arrangement. Keep everything which acts like an antenna as far away as possible from your house (and neighbouring houses), match the antenna to 50 Ohms at its best and use coaxial cables to bring the signals into the house. Place common mode chokes at the receiver's ant input and use good grounding at the receiver as well as near the antenna feedpoint outside. Computers sometimes need extra grounding and noise filters in their power lines. Some people even found it necessary to bury the coaxial cable as far as possible in the ground to avoid common mode noise from the neighbourhood entering the cable.
But this all of course does'nt help anything when the noise is picked up by the antenna itself.
The days when we could receive something inside or close to a building without noise are over.

73, Heinrich

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wa0aw
Posts: 1
Joined: Fri Apr 21, 2017 8:42 am

Re: New user question - please see my screenshot

Postby wa0aw » Sat Apr 22, 2017 10:35 pm

Hi ... had the same problem. Replacing the USB cable with one with Ferrites on both ends did nothing to help. After watching the system left on for several hours, I traced it down to the FURNACE in my home. I happened to be in the shack when the furnace went on, at the same time your screen shot started via the SDR manual turn off of the furnace confirmed the interference. Some clamp on ferrite beads on the power lines going to the furnace controller killed it dead ! The RSP-2 is better than the RSP-1 against interference, but it is still highly susceptible ... Be aware, it could be anything with a microprocessor or switching controller in your home or your neighbors if they are close to your antenna ...

Good Luck - 73
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