https://www.sangean.com/products/product.asp?mid=73&cid=10
I don’t know a lot about the Sangean ATS-909X receiver, but here is the web site. Based on the short video, there is an external antenna jack, but I don’t know what kind of connecter it uses (proprietary or common). At those really lower frequencies, the wavelength is quite long so for that, the longer the antenna, the better.
The functions are very similar to the 818 and my antenna is 80m. Im happy