Thank you, Jim. I was going to refute some of the comments by K4TAX and
W0LEN myself, but I'm getting tired of challenging every bit of antenna
misinformation that shows up here.
73,
Dave AB7E
On 3/17/2020 4:42 PM, Jim Brown wrote:
On 3/17/2020 3:30 PM, Lyn Norstad wrote:
One simple post, Bob, and you've covered pretty much everything
anyone needs to know about wire dipole-type antennas.
NOT! While non-resonant dipoles are certainly viable transmitting
antennas, there is FAR more to know about them, including:
1) Their directional patterns are different on every band;
2) They have very poor rejection of common mode noise on the feedline
unless choked at the FEEDPOINT (i.e. where the feedline connects to
the horizontal wires) and I know of no practical choke to do that
effectively.
3) #2 is true because in the common mode circuit, the feedline is part
of the antenna unless the choke disconnects it, and it can only do
that at the feedpoint. The only thing that a choke can do farther down
the line is add high impedance to that common mode circuit, creating a
current minima at that point. Remember, it's an ANTENNA, not a simple
series circuit.
4) A well-balanced transformer coupled tuner CAN present an open to
the common mode circuit, but the rest of the feedline is still part of
the antenna, so any common mode noise received on the feedline is
coupled to the antenna, and from there back down the feedline as a
differential signal.
5) Many years ago, N7WS published his research showing that window
line gets pretty lossy when wet. It's in one of ARRL's excellent
Antenna Compendiums.
Bottom line -- this is one of those antennas that "works," but how
well it "works" depends on your local noise level and whether the
station(s) you want to work are in one of the nulls of its pattern.
It's one of those antennas that was a lot better idea 20 years ago
when it was highly advocated by smart engineers when noise levels were
a LOT lower for most hams than they are today.
73, Jim K9YC
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