Can a a signal be too strong ?
Yes sometimes.
The KiWi has a limited dynamic range, and is being presented with just about every signal you could throw at it over the 0-30MHz instantaneous bandwidth it is capable of receiving.
As a rule of thumb if the noise floor on a quiet bit of spectrum increases by 6 to 10dB when a antenna is connected, then that is the optimum level.
With active antennas the test is a bit different as the electronics will also add to the noise floor.? So ideally you would check the increase in noise floor by connecting a screened inductor, with the same value of inductance as the actual loop, in place of the loop itself. Then measure the noise floor, reconnect the loop and check to see by how much the noise level increases.
The higher the noise floor is above the rule of thumb value of 6dB, the less dynamic range you have available, but the signal to noise performance hardly changes.
What you will probably find is that the noise floor on the HF bands increases by 6dB, but that when you check the LF bands it increases by 20dB or more, which is excessive.
The trick is to use an attenuator that has a decreasing value with increasing frequency. This is sometimes called a slope amplitude / frequency equaliser, and it's very simple to make.
Something like this circuit works well. The resistor values are chosen to provide the required attenuation on the lowest frequencies, in this case it's approximately 10dB.
Clint KA7OEI, has a good blog post on the subject, including some other circuits.
Regards,
Martin
