For those initiated, some words about it below:
The radio was initially equipped with just a 10meters long aerial. It had some coupling (3meter long wire for counterweight, for example etc.), but did not have any tuning. Neither wa sit with any sufficient length. As the frequency we are receiveing is 4.625MHz, it will make the wavelength of 71m, which makes any decent antenna on that frequency at least 71/2=35.5 meters long.
The other problem was noise. The signal received was not that bad, but it was overcrowded with all sorts of urban noise (worst of it radiating from plasma TV back to the mains cord!).
I spent about a week with my three shortwave antenna books, and finally decided to give a try on magnetic loop, before I start climbing on the neighbours roof.
The result - two nights of building and ... the result is really amazing. It is not that much more sensitive han the long wire was, but it has two stunning propoerties: First - it has almost no noise, as it is tuned to exactly the right frequency. Second -it has excellent directional characteristics. Which is of course why these types of antennas were used for directinal radio navigation for ships and military all the way until mid-80s.
I will post the details for the antenna here later. This antenna is not suitable for random shortwave hopping, as you have to tune it and turn it for the exact bearing and frequency to make it work.
However, if you know the frequency and know what direction it is, I would definitely recommend building one! I can not imagine anything else for 80m band fitting in your room and giving even remotely the same result!