About my broadband vertical:
The radiator is a 10m high vertical 60mm aluminium pipe, completly insulated from ground.
The counterpoise are about 10pcs of 10m long wires, horizontal 1-2m above the ground (elevated radials)
I connected a high impedance input pre-amp directly between elevated radial network and the vertical. The input of the pre-amp is carefully balanced with a very high mu torroid, to prevent IM2 products in the electronics.
The output of the pre-amp drives CAT5 cable heavily choked and bypassed to prevent common-mode interference in the high imp. pre-amp..
The system is very sensitive against common-mode problems due to the pre-amp which is sensitive for common-mode (unwanted noise) and differential-mode signals (antenna output).
Output of the pre-amp is that high, that you need 15db of attenuator in front of a todays sdr receiver (for example ELAD FDM-S2)
Mediumwave band ist full of -10dbm signals, although no local transmitters.... nearest transmitter ist about 100km and not very high power.
Due to the pre-amp, the antenna is very broadband, as the high impedance of the pre-amp does not load the induced voltage a lot but can drive my feed-cable with good match (Belden Cat5E has about 110Ohm impedance which is matched to 50Ohm in front of the receiver.)
For NDB bands and also DGPS reception, I use my QS1R SDR-receiver. This receiver does not use a active front-end, so it is very well suited for extremely strong signals (overload at about +9dbm).
Ulli, ON5KQ