Possible problem with device? Interference throughout the whole spectrum

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chemesherpa
Posts: 2
Joined: Mon Aug 10, 2020 11:10 pm

Possible problem with device? Interference throughout the whole spectrum

Post by chemesherpa » Mon Aug 10, 2020 11:51 pm

I just got my kit yesterday from amazon. I have my antenna mounted outdoors in the vertical position, with the long antennas attached. I configured my device per the qsg and was able to pick up FM channels right away. I tuned down to an AM station that I know broadcasts in my area and couldn't hear it. I googled and saw that you are supposed to change the sampling mode so I changed to direct sampling (q branch). I then was able to tune the AM station... but i started to notice this sweeping noise on almost all frequencies from 0kHz all the way through 30mHz. See images below. It sweeps through.

I do not believe that this is from an external source because I have a portable SW radio and i do not hear this type of interference. I am able to pick up many stations including the time broadcasts on 2.5, 5.0, 10.0 mhz... I am unable to pick up on my SDR dongle at all.

The noise level is so high on almost every channel it is hard to pickup anything in the SW bands.

Any ideas?

Edit: Also I am noticing that I am picking up local broadcast stations on weird frequencies.... for example I am picking up a locally broadcast medium wave AM station AM 1340 on 27.46 mhz. (also another copy on 35mhz, 52.26 mhz...)
2020-08-10 18_13_24-SDR# v1.0.0.1732 - RTL-SDR (USB).jpg
2020-08-10 18_13_24-SDR# v1.0.0.1732 - RTL-SDR (USB).jpg (708.46 KiB) Viewed 378 times
2020-08-10 18_22_11-SDR# v1.0.0.1732 - RTL-SDR (USB).jpg
2020-08-10 18_22_11-SDR# v1.0.0.1732 - RTL-SDR (USB).jpg (1.33 MiB) Viewed 378 times
2020-08-10 18_30_13-SDR# v1.0.0.1732 - RTL-SDR (USB).jpg
2020-08-10 18_30_13-SDR# v1.0.0.1732 - RTL-SDR (USB).jpg (1.63 MiB) Viewed 378 times

rtlsdrblog
Site Admin
Posts: 2743
Joined: Mon Nov 19, 2012 11:54 pm

Re: Possible problem with device? Interference throughout the whole spectrum

Post by rtlsdrblog » Tue Aug 11, 2020 11:42 am

Please remember that the Q-branch direct sampling mode is limited in performance.

Due to Nyquist you're going to get a mirroring of signals centered around 14.4 MHz, so it's normal to see broadcast AM up at 27 MHz.

The interference just looks like normal interference from electronics to me, it could be made worse due to the Nyquist mirroring.

You're not receiving SW stations because you're using the dipole antenna. The dipole antenna is only intended for VHF/UHF operation. It will not work for HF frequencies. For that you need to have a proper HF antenna which will be large/long, or some sort of magnetic loop. Your shortwave radio has a built in ferrite loop antenna tuned for the HF bands.

chemesherpa
Posts: 2
Joined: Mon Aug 10, 2020 11:10 pm

Re: Possible problem with device? Interference throughout the whole spectrum

Post by chemesherpa » Tue Aug 11, 2020 12:36 pm

Thank you, I will try hooking to different antenna.

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