Hi

I was watching this UTube video to learn about modulation. At 02:31 it is said, "By the way you always want a capacitor before your antenna to protect your circuit and block any DC voltages the antenna may accidentally touch".

Okay. The capacitor would block DC voltage but it can also touch an AC source too. Above all lightning could also strike the antenna and this can produce AC voltage inside the antenna which would definitely damage the circuit. So, in my view, one should be more concerned about AC damage than the DC. Do I have it right and how do we protect the circuit from AC transients? Please let me know. Thank you.

Regards
PG

 

If lightning is a credible threat where you live, you install a lightning arrestor. There are different varieties, but a simple one consists of a spark gap -- one side hooked to the antenna driven element, the other to earth ground. This might not divert a direct hit, but will suffice for "ordinary" protection.
If lightning is not much of a threat, many people omit the arrestor, but it is still a good idea, and cheap insurance. Much cheaper than replacing a transceiver melted into slag.

 

Thank you for the reply, K7GUH.

Forget about the lightning. Most of the wires running around a place contain AC, not DC. So, the probability of an antenna coming in contact with AC is very high than with DC. The capacitor won't block any AC which means we are not secured against real danger and DC danger is just 'phantom' danger, in my humble opinion. What do you say? Please let me know. Thank you.

Regards
PG

 

You need to select a capacitor that is low impedance to RF, but high impedance to mains frequency. This should be easy, since the frequencies are separated by several orders of magnitude.
Where are you contemplating putting an antenna that might come in contact with AC?

 

You could select a DC Block. I have used them in my GPS set.

 

You could select a DC Block. I have used them in my GPS set.

Which is likely just a capacitor.

 

You need to select a capacitor that is low impedance to RF, but high impedance to mains frequency. This should be easy, since the frequencies are separated by several orders of magnitude.
Where are you contemplating putting an antenna that might come in contact with AC?

Hi Ron

Actually I'm not contemplating to put an antenna anywhere. While watching that linked video that point about the AC came to mind and I though I must ask about it.

Regards
PG