"whiskey-tango-foxtrot" moment while reading power point presentation on LORAN

[unclejed613]

https://web.stanford.edu/group/scpnt/jse_website/documents/Enhanced_Loran_rv2-short.pdf on slide 35, they say the antenna top has 0 volts on it, but the feedpoint has high voltage. that's backwards, the open end of an antenna is a current zero, and a voltage maximum... when visualizing standing waves on an antenna, you begin at the open end assuming a voltage maximum and current zero. at resonance, an antenna behaves as a series resonant circuit, so the current is maximum at the feedpoint, and voltage is low, because, at the other end of a 1/4 wave piece of wire (or tower) the current is zero, and the voltage is maximum. it's the same with a 1/4 wave open feedline section (open 1/4 wave stub).

 

[JimB]

I think the guy has his voltages and currents mixed up.

One of those things that you write, but when you look back later you think "Did I really write that!"

JimB

 

[unclejed613]

yeah, happens occasionally, thinking one thing but typing something completely different...

 

[JMW]

If I'm not mistaken LORAN stations have been decommissioned. They may have some in foreign nations.
It was a great system. The Apollo moon shots used it. I once read the accuracy was equivalent to shooting a pea from NYC, to S.F. and hitting the saucer as opposed to the cup.

 

[unclejed613]

actually, LORAN C is being recommissioned. several well known instances of GPS spoofing (which is very easy because of the very weak satellite signals can be easily overcome with a local transmitter with power levels of a few milliwatts) prompted the decision. LORAN C signals are difficult to spoof because of the large antenna structures and large amounts of transmitter power required to meacon a LORAN station (meaconing is a military term for spoofing a navigation beacon).