RTL-SDR not functioning properly at MW band

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safarinew
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Joined: Sun May 03, 2020 10:49 am

RTL-SDR not functioning properly at MW band

Post by safarinew » Sun May 03, 2020 10:56 am

Hey guys, I just bought an RTL-SDR and it's working agreeably at SW and FM frequencies each with proper antennas.

The problem, however, is in MW band, where it can only pick up 2 or 3 strong local signals (while my portable can easily pick up 15+ plus clear signals).

AND this does NOT improve even with a dedicated MW magnetic loop antenna attached.

What could be the problem? I wonder. Thanks.

rtlsdrblog
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Re: RTL-SDR not functioning properly at MW band

Post by rtlsdrblog » Mon May 04, 2020 10:02 am

What RTL-SDR, and what is the mag loop antenna design?

safarinew
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Joined: Sun May 03, 2020 10:49 am

Re: RTL-SDR not functioning properly at MW band

Post by safarinew » Mon May 04, 2020 1:21 pm

chipset: R820T+RTL2832U

antenna: tried both MLA-30 active loop and TECSUN AN-200 (for MW)

What's your assessment? Thanks.

RDPowers
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Joined: Mon Apr 27, 2020 9:41 pm

Re: RTL-SDR not functioning properly at MW band

Post by RDPowers » Mon May 04, 2020 4:02 pm

I think your problem may be similar to what I am describing in viewtopic.php?f=7&t=5725&p=14671#p14643

I am trying to receive AM signals on MW using direct sampling mode and am not having much luck.

I think the issue is direct sampling mode bypasses the tuner chip so you lose a lot of amplification and filtering.

My next step will be to generate some strong signals in the SW band (I am a licensed ham) and see if it is a signal strength issue or an AM demodulation issue.

Unfortunately other things are taking my time right now.

radiolistener
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Joined: Thu Jan 25, 2018 10:48 pm

Re: RTL-SDR not functioning properly at MW band

Post by radiolistener » Tue May 05, 2020 1:25 am

if you use original RTLSDRv3 it should work the same as usual cheap MW receiver.

safarinew
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Joined: Sun May 03, 2020 10:49 am

Re: RTL-SDR not functioning properly at MW band

Post by safarinew » Tue May 05, 2020 1:51 am

Thanks a lot, though i'm not sure we are having the same problem.
I'm new to this SDR thing. But you seem to know what you are doing. So hope you will have a while to sort out.

To be clear, my hardware is this:

https://www.amazon.com/Receiver-KKmoon- ... 47&sr=8-11

And my software is SDRSharp (Q channel sampling for AM)

alanzfq
Posts: 140
Joined: Thu Oct 04, 2018 11:18 am

Re: RTL-SDR not functioning properly at MW band

Post by alanzfq » Tue May 05, 2020 9:58 am

What does the supplier say?
Unless the direct sampling input is done well sensitivity can be very low.
Alan

RDPowers
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Joined: Mon Apr 27, 2020 9:41 pm

Re: RTL-SDR not functioning properly at MW band

Post by RDPowers » Mon May 11, 2020 7:01 pm

alanzfq wrote:
Tue May 05, 2020 9:58 am
Unless the direct sampling input is done well sensitivity can be very low.
I agree.

In the other thread I reference above, me and IyoKobat have made MW AM signal reception work using the gqrx software.

The issue with low sensitivity is that direct sampling bypasses the tuner chip on the rtl-sdr device, which bypasses the low noise amplifier and the signal rejection and intermediate amplification done by the tuner chip.

If you look at the diagram at http://aaronscher.com/wireless_com_SDR/ ... _info.html you can picture what I am saying. In essence the tuner chip on the left is being bypassed when in direct sampling mode. You need to replace its amplification and filtration functions to get a strong signal.

I think the rtl-sdr device is excellent considering its low price point but really limited in the radio bands below 30 MHz or so. I will say that I am glad it has the direct sampling mode, it's good to be able to decode some AM broadcast band signals for demonstration use if nothing else. However you need to be aware it has issues especially near 14 MHz and 28 MHz which is unfortunate since these are commonly used for amateur radio work. To do better you will need to consider getting a front end up converter such as 'Ham It Up' or a SDR that uses a different architecture to access frequencies below 30 MHz.

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