What is load on an antenna? Is it safe to short the antenna port?

Question

On the readme page of https://github.com/pwarren/rtl-entropy, it says:

If you're serious about the cryptographic security of your entropy source, you should probably short, or put a 50 Ohm load on the antenna port, and put the whole assembly in a shielded box. Then you're getting entropy from the thermal noise of the amplifiers which is much harder to interfere with than atmospheric radio.

How do I put a 50 Ohm load on that port? Do I just put a resistor of 50 Ohm on the port? Can I safely short the port (connecting both parts with a copper wire)?

Answer 1

The section you quoted appears to be referring to the antenna connection of a receiver. Yes, you should be able to either short the antenna input or connect 50 Ω there. The point seems to be that you don't want ambient RF affecting the noise source used for cryptography, since that give someone else the ability to affect it.

50 Ω is presumable the impedance of the antenna input, so that would match it. It practice it matters little whether the antenna input is shorted or terminated at its impedance.

Answer 2

Shorting or connecting a 50 Ohm terminator amounts to the same as putting it in a shielded box, just leaving a co-ax connector open will also result in very little pickup. All these options will eliminate input from the circuit.

Trying to manipulate cryptographic results by skewing an entropy source is so on the fringe of feasability that it is not worth worrying about it in any case unless you are researching long term statistical bias.