That's not true. Active monopoles work fine both on top of metal masts and non-conductive masts.ON5HB wrote:So if you put it on metal pole the pole acts as an common-mode-choke and the "antenna" stops working.
This is true. That's why an active monopole is always a compromise. The higher it is mounted above ground the stronger the signals are (especially on VLF...MW), but on the other hand the coax cable as the counterpart of the plate/whip shows more and more resonances on the shortwave bands which make some frequencies appear stronger, others weaker.ON5HB wrote:because the coax cable is part of the antenna.
All owners of mini whips have been going through long periods of experiments to find out the best compromise for height above ground and size of the probe element. Those only interested in VLF...MW put it on masts appr. 8 m above ground (or more) and ignore the bumpy frequency responce on shortwaves. For a balanced frequency response for all bands (VLF...SW) a height of appr. 3 m above ground seems to be ideal. In both cases the probe consists of 1 m rod or appr. 80 cm² metal plate. Smaller probe sizes will of course give different results.
This is partly true. When the probe is bigger and you live in a noisy environment (true for most of us), both signal and noise rise. The SNR remains the same. A big plate/rod increases the danger of receiver and/or amplifier overload.ON5HB wrote:Also, the bigger you make the plate/wire the worse electric spikes are fed into the receiver.
The antenna is the sum of plate/rod, coax cable, amplifier/impedance transformer and grounding. An active monopole is a delicate antenna. I needs some experiments to find the optimum dimensions for the individual location.ON5HB wrote:The plate/wire isn't the real antenna, the coax is mostly.