Comments on: Weather forecast on shortwave

By: Raffa

Raffa — Wed, 08 Feb 2012 14:40:00 +0000

Semmoinen Degen DE31 active loop. Häiriötä tulee kuitenkin myös käyttämällä pitkää lankaa antennina

By: Antti Autio

Antti Autio — Wed, 08 Feb 2012 14:19:00 +0000

Moi!
Minkälainen aktiiviantenni sulla oli tässä..?

t. Antti

By: edo

edo — Wed, 08 Feb 2012 12:36:00 +0000

Well, that’s what I’ve been doing lately in my job: removing ground loops and noise. So now I reached a ~10 nV noise on my sample and I removed the ground loop that caused a signal few orders of magnitude larger that what I measure now.

And I like to fix this kind of things: I’m not an expert in electronics, but I like when I manage to do what I want!

By: Raffa

Raffa — Wed, 08 Feb 2012 10:18:00 +0000

Yep. Actually I could easily make a low pass filter with 20/30 kHz cut-off frequency, or even less, since the transmission bandwidth is just 4 kHz. I’ll let you know. Didn’t know you were interested in this kind of stuff!

By: edo

edo — Wed, 08 Feb 2012 10:14:00 +0000

Looks to me that this is a mere interference by means of the cable rather than a ground loop. To test this it’s sufficient to operate the radio on batteries and/or the laptop.

I would try with a low pass filter. I do this on my experiment.

By: Raffa

Raffa — Wed, 08 Feb 2012 12:14:00 +0000

There is a discussion going on in the DE1103 forum: also there they say to separate the grounds. I start to wonder whether the ground loop separator I bought is not working properly. I might buy the stuff and build it by myself

By: Raffa

Raffa — Wed, 08 Feb 2012 11:59:00 +0000

The radio gets back interference from the laptop. If I switch off the LCD screen, the interference disappear. Furthermore, also the laptop charger makes interference. Actually I have to work on battery, otherwise I can’t hear anything from the radio. All this when the audio cable is plugged, of course.

By: edo

edo — Wed, 08 Feb 2012 11:35:00 +0000

Again! You plug the audio output of your radio to the line-in (mic-in) of your computer. Does the radio get audible interference? Or is just the signal into the computer that is noisy. Let’s for a moment forget the RF noise radiated from the screen.

By: Raffa

Raffa — Wed, 08 Feb 2012 15:10:00 +0000

Actually the sources of interference are two: one on RF (the screen, for example, increases the noise of the received signal in the radio, also with the audio cable unplugged), one through the cable when plugged. One possible explanation for the latter is that the laptop doesn’t have a line-in, but only mic-in, which makes me thing that that input is active (amplified), thus the increased noise. With a ground isolator that should be solved, though. But it isn’t.

By: edo

edo — Wed, 08 Feb 2012 09:56:00 +0000

Ouch!

If the interference comes from the cable itself you may filter with a low pass filter, since you need low freq audio and the LCD will be presumably above 100kHz (my guess is that the noise comes from the inverter).

—-/\/\/\/\/\—-o—–
|
—
—
|
—- GND

the cutoff freq (-3dB) is 1/sqrt(RC). You’ll have to adjust the values to an appropriate freq and low resistance (but then you need a high enough capacitance!).