downconverter damaged

[sine_help]

Hi

(a) What are the main or most common causes of damage of downconverter PXI 5600. specially mixer ic and other 

     components that are contected directly to RFinput pin.? i am using VHF antenna . my first damaged

     downconverter is showing 20dbm loss in every signal and other dont show any signal .in both cases PXI  and

     antenna was properly grounded.

(b) Is there any affect on working of downconverter PXI 5600 if system is not grounded. if yes than how can i use it

     in moving vehicle where proper ground is not avaliable?

(c) Why it is necessary to have neutral to ground voltage less than 1V? Is there any relation of burning of Mixer ic with

     voltages on neutral terminal of power supply eg. if neutral to ground voltage is 5V or 10V can this burn MIXER IC at 

     RF input? 

(d) Is there any way that antenna has DC voltage on it. downconverter has max 0V dc at input. if system is working

     fine with antenna, what would be causes of sudden appearance of DC voltage on antenna like through induction

     etc?

(e) Can polarity of AC supply can affect the working of downconverter or can it damage RF input?

(f)  Can ground loops can damage RF input ? if yes then how ?

(g) It is said in Downconverter 5600 manual(input/output Downconverter Front Panel) that input Maximum input DC

     voltage is (+,-) 5V how this is calculated?

(e) Also when it is said in same manual(Amplitude) that maximum DC Input voltage =0VDC then how come above

    statement is true.

Please answer one by one .