![]() “Dude, Some moron built a wall inside this tunnel!!” “Yeah, I think the author was trying to illustrate a point about reflections” “Lovely brickwork on those entrances though” In VNA parlance, we will call this a S21 measurement, meaning we have made a measurement of a signal at port 2(your friend) of a signal injected at port 1(your beautiful voice). You have just measured the ‘thru’ characteristics of this tunnel. Maybe there is some material in there that is absorbing the high pitch noises, or closed service tunnel that has created a resonance. Perhaps, we can detect a difference between the high and low pitch sounds. We might be able to work out the length from the volume and delay(you were careful to synchronise watches) of the received sound. You have a great idea! What happens if I shout into the tunnel and have a friend listen at the other end. We will assume that you don’t want to go in, because, well, your scared of the dark and don’t want to be hit by a train. Say you are standing at on end of a dark train tunnel and want to know something about what is inside. For an alternate analogy take a look at KirbyMicrowaves site. That sounds pretty complex, but it’s really not. “Atrévete a Entrar…”by Hadrian Fernandez is licensed under CC BY-NC-SA 2.0 ![]() It doesn’t hold a candle to the performance of a instrument grade piece of kit, but for the price, and used with care, it’s not too bad.Ī VNA is designed to inject a known frequency and amplitude source signal into a RF port and measure the relative amplitude and phase of this signal when received at a number at one, or more of it’s ports. ![]() Luckily, there are cheap alternatives now, such as the NanoVNA. ![]()
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