[Elecraft] Off-Topic: Your advice/suggestion about antenna

[Jim Brown]

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