DC Pass, DC Block Lightning Arrestors? 1

[candyclaws]

I use lightning arrestors between radio antenna and transceiver, like Andrew APG-BNFNF-350, for marine radio equipment such as VHF, MFHF, UHF, GPS.

I understand that DC block lightning arrester is to block DC frequency interference, but there is likely no DC interference between matched radio antenna and transceiver. Why cant we just use DC PASS lightning arrester for all radio antennas?

On what circumstances DC block lightning arrester have to be used instead of DC pass?

 

[VEBill]

Lightning strikes (and related phenomenon such as 'leaders') obviously have a very large DC component - think about it: they originate from a type of 'static' electricity in the clouds. (They also have some AC (RF) components when striking, which is why you can hear them crashing on an AM radio.)

Inside a lightning arrester is a parallel element triggered by high voltage and intended to bypass as much current as it can to ground. But there will be a residual voltage across this device; either from the inherent voltage drop of its internal physics (perhaps a gap, or a little gas tube); or I*R voltage drop from its internal series resistance. In the event of a strike (or similar), there would be a moderate voltage presented across the radio side of the protection device.

So if your system doesn't need DC continuity through the protection, then you might as well use a DC Blocking device with its internal series capacitor. It'll help (maybe) with protecting the radio (or whatever) from lightning.

Note: If the coaxial cable is also being used to provide power to the LNA within the antenna (e.g. GPS), then you normally can't use a DC-Block in the antenna circuit.

Complete protection requires a Systems Design approach. It can get complicated.

 

[candyclaws]

VE1BLL many thanks for advice.