Andrea Baldoni wrote:
. . .
2)
build circuits with so high dynamic range that's completely impossible to
have input signals overload them (what's the dynamic range one should
normally expect at the antenna input, excluding obvious limit-case situations
where the transmitting output is fed into the receiver input...?)
. . .

One night I heard audio in the background when listening to my direct
conversion 40 meter receiver. It was designed specifically to be as
immune as possible to AM demodulation, and since I had finished its
optimization several years before, I hadn't heard any audio from
demodulated AM. (It was common when I was using mixers with poorer
balance and dynamic range.) It didn't take long to find the station with
my home receiver. It was at about 7335 kHz, a religious HF broadcast
station in San Francisco (about 600 miles from here). The broadcast was
in Russian, so they were evidently beaming to Russia and I wouldn't be
far off the main beam.

Some careful measurements showed a signal strength of 250 mV RMS at my
receiver terminals. (That's 74 dB over the typical S9 value of 50 uV.) I
was using a vertical 4-square array, which isn't at all optimum for that
path. I hooked the antenna directly to my oscilloscope and could see the
carrier and modulation.

I took the receiver on a visit to England, and heard the audio from a
large number of AM stations in the background, so I believe the signal
levels there from HF broadcasters commonly exceeded the 250 mV I saw
only once at home.

The problem can of course be reduced by use of very narrow filters, but
they're often so close to the 40 meter band edges that even that
wouldn't be enough in most cases.

I've also encountered some staggeringly strong signals when operating
Field Day, when a group with a high or even moderate power transmitter
is on the next ridge or otherwise very close.

The bottom line is that I'd be hesitant to trust just about any number
for a "worst case" maximum signal strength. Be sure to test any proposed
design on 40 meters for a while from your location in Europe.

Roy Lewallen, W7EL