Dick Grady AC7EL wrote:
On Mon, 16 Jun 2008 23:10:31 EDT, (Mark Kramer) wrote:
In article ,
Bill Horne wrote:
Wouldn't the coverage be improved by phasing the
antennas so as to maximize radiation toward the horizon?
Depends on the coverage you want. You want far away? Aim for the horizon.
You want 100-200 miles? Aim up.
NVIS is great for in-state communications.
However, the object of Field Day is to contact as many stations as possible.
Using a NVIS antenna will severely limit the number of stations which can be
contacted.
An NVIS antenna is usually referring to a low dipole. There are a lot of
misconceptions about the antenna. They do work on DX (just not as well)
and they make a pretty fair Field day antenna.
The reasons are that they radiate fairly equally in all angles, as
compared to a similar antenna at a height that would allow it to have a
lower radiation pattern. This might sound odd, but if you model an NVIS
antenna, then compare it to a higher one you'll see that is the case.
I think that we some times get tricked by terms such as "Take off Angle"
or similar terms. That dipole is radiating in all directions. Some just
not as much as others. That can get us thinking that the signal comes
off the antenna as a "blob" that is heading out at some ideal or
non-ideal angle.
People have earned DXCC using NVIS antennas.
To complicate matters, Propagation effects are not static. I performed
experiments a few years ago, using a dipole which was NVIS on 80/75
meters, and a Vertical antenna (Butternut HF6V) to answer the perennial
question " Which is better, a horizontal or a vertical antenna?" In
receive mode, I used a decade attenuator box. To transmit, that has to
be removed, lest I get a smokey crunchy attenuator.
Which is better? The answer is a resounding yes! And not always in the
way we would think. The propagation effects made the dipole perform
better sometimes when I expected the vertical to, and vice versa.
What's more the conditions can change in the middle of a QSO. I had many
cases of fading, when the Op would mention how the band was changing.
Switch from vertical to dipole, or vice versa, and it brought the signal
back up. Note I'm not saying that this will compensate for the band
closing up.
So that NVIS antenna might not be so bad for Field day as we may think.
It won't have as much oomph at lower takeoff angles as the low takeoff
angle antenna will, but it will have output at those angles none the less.
- 73 de Mike N3LI -