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Re: MW antenna for RTL-SDR V3
Just my proposals :
There is the AN200 tuned loop antenna for MW that does great work for portable radios. I tested it once to my RSp1a that didnt work as expected because the design of digital DSPs is very different It is very cheap from Hong Kong via Anon Co with 14USD plus shipping
You can see on how it works in my YouTube page https://www.youtube.com/playlist?list=PL12803A0C1E2082A4
For wide band SDP receivers as the RTLSDR ,SDRPlay or Airspy etc you can use the new Youloop from Airspy . https://airspy.com/youloop
or even the new 'legendary' loop MLA30 that uses a inbuilt preamp in around 25-40Eu available from ebay https://www.ebay.com/itm/383162242361
hope that it helps !