The antenna you use is all important..
But reading through the stuff online it appears that the design of this device likely could be improved substantially - that they could have done better.
I have the device they were selling before, but I assembled it myself. They didn't assemble it. And it was a major PITA, so much so that I have avoided doing anything with it since then.
Generally, it holds its own against any of the similarly priced (consumer level) portable shortwave radios - including the quite decent better Tecsun models,
with a decent antenna. Which they also need, to be honest.
But from what I am reading it likely could be improve quite a bit.
Here is their doc file..
Maybe this link will work:
http://115.28.16.44:81/file/3156.docThat is their instructions for it.
There also seem to be quite a few videos online of the earlier device, its construction and operation. Look at how it works in the Youtube videos of it. It is what it is.
It seems that the bypassing and their choice of parts could be improved a lot.
Start out learning a bit more about rtlsdrs, notably that they are vulnerable to noise and USB connections are inherently noisy already with VHF. On HF they are even more noisy.
I put lots of ferrite cores on my USBs when I use SDR.
Also to get decent reception I needed a long wire, a good ground,
and a 9:1 unun.
To be honest with you, despite some moments of decent reception everything RTLSDR have always made for marginal shortwave receptionfor me where I live because its so noisy.
Ive had much better luck with a different SDR probably because it has much more dynamic range and better rejection of noise and out of band signals.
Lacking an antenna tuner, a unun makes all the difference.
That applies pretty much to all my receivers, all of which are SDRs. I live in a very noisy suburban location.
All of that said, likely anybody with any decent amount of RF experience could likely find areas for improvement on the Ba5SBA design.
Russian web pages go into length about this but not having actually trying any of these changes.
I would try using a different RF transformer. I would use a binocular core, or perhaps two or even four side by side instead of a toroid. Thats a better broadband transformer. And I would try more turns on the balanced input side
You should make a post asking for other people's opinions on what the best transformer to use would be.
Maybe you might also want to experiment with different materials, or maybe even commercial RF transformers..
I bet you could improve the performance significantly. Iam reluctant to on mine because there si a limit to how many times the little wires can be resoldered I am sure. It will become impossible to fix.