[Elecraft] Sloping Terrain vs Feedline Losses

[Guy Olinger K2AV]

1) For the low bands, the overwhelming consideration is reduction in near
field losses, both dielectric and I squared R (I2R) losses.

2) We need to remember that for non salt water situations vertically
polarized RF is NOT reflected from dirt and rock. For all intents and
purposes it is absorbed. Vertically polarized reflection enhancement
happens over salt water, but certainly not over rocky or rock-based
surfaces.

3) Feedline loss is an issue for distant antennas, **particularly** what
the loss will become long term, after extended exposure to the environment.

4) On the low bands are 1/4 wave radials are really the great deal on low
bands that ham mythology says they are? We need a counterpoise, and 4 by
1/4 wave radials are only *one* choice with little to recommend it except
simplicity at the feedpoint. The worst thing about many counterpoise
schemes is that they induce current in the ground, and that is loss. The
mechanics that govern the induction are a bit murky and not at all well
known. We need a counterpoise to store electrons for a half cycle. Whether
that device is naturally resonant on frequency only saves you complexity at
the feedpoint. What you will be stuck with permanently is however much LOSS
is invoked by the design.

Again, the word is LOSS.  Mitigate loss in your complete antenna *system*
design. Regarding your particular situation:

Stand at your two possible installation points. Look at your most distant
horizon in any important direction. ANYTHING below tree top, or mountain
ridge-top line, even 15, 30, 50 miles away, is severely attenuated, if not
lost to -30, -40 dB effects. If you have a clutterless view to distant
horizon, for vertical polarization this will advantage you the most because
it removes dielectric and I2R lossy clutter in the path to very useful low
angles. Remember that reflection enhancement in your situation only applies
to horizontally polarized antennas.

Designing your antenna, 1) use a counterpoise with least loss from ground
induction, 2) move the RF current maximum up on the vertical conductor, 3)
**expect and prepare yourself** for matching a miscellaneous impedance at
the feedpoint. This misc feed Z is most likely for the best combination of
1) and 2).

If you really are concentrating on efficiency, get the current maximum up
in the air, and use a low ground induction loss counterpoise.

If you go distant installation due to clutter considerations, PAY UP for a
permanent hardline coax feed, unless you are willing to put up ***BARE***
wire open wire feedline you construct yourself. Buryflex flooded coax would
be a medium solution but has all the critter and outdoor accident issues.

Commercial balanced line deteriorates in time. Been there, done that, never
again. Even with the open wire, you can have common mode issues on the
balanced line nearly impossible to rectify, unless you take steps in the
last quarter wave or so before the antenna. The balanced feedline run will
need to be an odd multiple of a quarter wave accounting for velocity
factor.

Common mode current on the line will go almost entirely to loss.

73, Guy K2AV

On Tuesday, July 12, 2016, Dauer, Edward <edauer at law.du.edu> wrote:

> So long as antenna discussions on the reflector haven’t been met with the
> “OT” cloture lately, I have an antenna question of a different sort.  I am
> contemplating a ¼ wave vertical with four elevated radials for 80 meters.
> My choices for siting it are two – one is near the top of the property
> (about 8,600 feet ASL), somewhat in the clear, and within 100 feet from the
> operating position.  The other is in a meadow near the property boundary,
> which is much more open and a just a bit higher – but it has two other
> significant characteristics.  One is that the land slopes away from that
> site, over about half the compass from NNW to SSE, at a slope of 10 to 15%
> for about a half mile.
>