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PC (laptop) power induces significant noise

Posted: Thu Mar 10, 2016 1:45 pm
by DerekR
I purchased the SDRplay two days ago, and am using it with SDR console on a new HP I5 laptop. For now the antenna is simply 50ft of hook-up wire strung out the window. I am delighted with it so far. However, I find that whenever I unplug the power supply (so it is running on battery) the noise floor drops by more than 20 dB, and the HF device performance becomes "alive".

Is this a problem with the lack of ferrite beads on the USB cable, or the lack of coax feed to the antenna, or possibly a noisy power supply? Any suggestions?

Thanks,
Derek

Re: PC (laptop) power induces significant noise

Posted: Thu Mar 10, 2016 3:36 pm
by WhoaNellie
I think you're already on the right track - it could be any combination of the three, or all of them. Trying to isolate them one at a time is about all you can do.

If you have a small portable radio that receives SW and/or the AM BCB, you could tune it to some frequencies of interest and move around with it to determine where the interference from the power supply is the worst and the least. By seeing how much that radio is affected with the power supply on and off you can get a good idea of how much a coax feed-in might help improve things, and you can determine how long it should be by moving around with the portable radio. Using a coax cable could be a cheap and effective solution, you just have to see.

Re: PC (laptop) power induces significant noise

Posted: Wed Mar 16, 2016 9:25 pm
by dlritter
I found that the 'stock' power supply for my Gateway was very noisy. However, my IGo travel supply is quiet.
Good luck.
73
David

Re: PC (laptop) power induces significant noise

Posted: Thu Mar 17, 2016 1:34 pm
by K4KDR
I noticed the same thing some time ago when unplugging the power cord from my Dell laptop.

I put a couple of snap-on ferrites on the cable between the transformer & the laptop and the noise disappeared.

-Scott, K4KDR
Montpelier, VA USA

Re: PC (laptop) power induces significant noise

Posted: Sat Sep 02, 2017 10:58 am
by IZ2245SWL
The same for me with a brand new Lenovo Yoga. I have a big FT-240 31 ferrite choke with 12 turns on the usb cable added to their two ferrites built in. I made the same on the power supply cable. The floor noise improves but it is not good as the batteries one.

Re: PC (laptop) power induces significant noise

Posted: Tue Oct 03, 2017 1:16 pm
by EastPier
I have the same issue and run the laptop unplugged, however I'm still plagued with interference across all band - but worst on HF, see below. I've wrapped the USB through a ferrite ring - with no effect (again, laptop is unplugged). My head is wrecked, as I have excluded any LEDs in the house etc. I live about 100m from transmission lines and I'm wondering could this be it?

Many thanks in advance for any ideas

73 Adrian

Re: PC (laptop) power induces significant noise

Posted: Tue Oct 03, 2017 2:32 pm
by DanubeBCL
EastPier wrote:I have the same issue and run the laptop unplugged, however I'm still plagued with interference across all band
Hello,
a typical pattern of switched mode devices, mainly switched power supplies. Harmonics spaced between appr. 15 kHz and appr. 100 kHz, depending on the device. We all have such patterns (more or less) in our receivers. When your own house is "clean" they certainly come from neighbouring houses. I myself, for example, "receive" harmonics from switched power supplies in a distance of 80 metres with S8. Yes, transmission lines can carry the noise and help to distribute it. But very often the noise is coming directly from the power lines in neighbouring houses.
You can (in case the source is not your own house):
1. Talk to your neighbours and persuade them to install filters. But they will not understand and ignore you.
2. Call the authorities. But in many countries noise free radio reception is no longer on their agenda as the politicians say, classical radio reception is no longer required. You have the internet to listen to radio stations. And the level or your noise with appr. 10 dB above noisefloor is very low. No reason for any authority to take action.
Switched power supplies are only the tip of the iceberg. There are a lot more sources, like power line communications (PLC) and all the rest. And there are more to come soon: Charging docks for pedelecs and (extremely evil) electric cars with powers of 20 to 100 kW and Wireless Power Transfer.
73, Heinrich

Re: PC (laptop) power induces significant noise

Posted: Wed Oct 04, 2017 3:14 pm
by F1BJB
PC monitors or their cables can also produce interference
A trick is to start a recording then switch off and disconnect everything from your PC : keyboard, mouse, monitor,speakers , etc
Then play back the recording.
Of course for a laptop you are limited :)
I also found that sometimes interference is radiated by a parasitic dipole or loop.
In my case a portable TV/DVD player was just charging from a wall adapter and disconnecting the
TV aerial greatly reduced the interference.
I just connected the ground of mains socket to the shield of the TV coaxial cable socket.
Thus shorting the parasitic dipole or loop depending if the TV coaxial was already grounded somewhere.
Of course previously I had tried a lot of complicated ,expensive, big , over rated and less efficient mains filters :)

Re: PC (laptop) power induces significant noise

Posted: Sat Oct 07, 2017 10:45 am
by EastPier
Thanks very much Heinrich, food for thought. Guess all I can do is eliminate what I can. 73 Adrian

Re: PC (laptop) power induces significant noise

Posted: Sat Oct 07, 2017 10:49 am
by EastPier
F1BJB wrote:PC monitors or their cables can also produce interference
A trick is to start a recording then switch off and disconnect everything from your PC : keyboard, mouse, monitor,speakers , etc
Then play back the recording.
Of course for a laptop you are limited :)
I also found that sometimes interference is radiated by a parasitic dipole or loop.
In my case a portable TV/DVD player was just charging from a wall adapter and disconnecting the
TV aerial greatly reduced the interference.
I just connected the ground of mains socket to the shield of the TV coaxial cable socket.
Thus shorting the parasitic dipole or loop depending if the TV coaxial was already grounded somewhere.
Of course previously I had tried a lot of complicated ,expensive, big , over rated and less efficient mains filters :)


Thanks F1BJB, I have an indoor amplified loop antenna that's always plugged in, I'll give it a go. Many thanks for the ideas, 73 Adrian