Agree with your points. I've said for a couple of decades now that one
of the least expensive ways to improve a modest station (assuming one
has at least a decent antenna) is to add an amplifier. Lots cheaper
than a bigger tower and a bigger antenna.
Also, to your point about arrival angles ... HFTA calculates a "figure
or merit" for several common paths. N6BV (the author of HFTA) ran a few
thousand simulations in VOACAP between various parts of the world for
the parameter TANGLE ... the optimum takeoff angle for that path. He ran
it for every month of the year over a full sunspot cycle (typical solar
fluxes) for each path to generate a statistical profile of the
normalized signal strength for each takeoff angle. I believe the data
for those profiles is included with the ARRL Antenna Book. HFTA's
"figure of merit" for a particular antenna over a particular terrain
overlays the calculated radiation pattern over that VOACAP statistical
profile of takeoff angles and sums the combination for each angle.
For example, N6BV ran 121 TANGLE calculations (12 months and 11 years)
from W7 to Europe, compiling the signal strength at every degree of
elevation for each of the 121 runs. Adding up the strengths for each
angle and dividing by 121 gives the statistical profile for the TANGLE
calculation. Overlaying the HFTA radiation pattern for the terrain
profile pointing from W7 to Europe onto the TANGLE profile, and then
adding up the result for each degree, gives the HFTA Figure of Merit.
The net result gives an interesting assessment of the antenna/terrain
for a particular path taking into account an entire sunspot cycle.
That being said, TANGLE is an empirically generated projection based
upon actual data taken during the International Geophysical Year and
other times, and one of the key scientists who worked on VOCAP and
adapted it for general use (Greg Hand) has pointed out that of all the
20 or so parameters that VOACAP can produce, TANGLE is probably the
least rigorously substantiated. Still, I think that HFTA Figure of
Merit offers a useful assessment of the combination of horizontally
polarized antennas and terrain for a desired path. I've used HFTA quite
a bit, and my on the air results subjectively correlate quite well with it.
73,
Dave AB7E
On 7/15/2016 12:16 PM, brian wrote:
Guys,
There is another issue here.
That is :
Just because ones antenna pattern is inferior to an optimum one by 5
or even 20 db at the best arrival angle, that doesn't mean there is
zero energy at the most important arrival angles. It just means there
is less.
QRPers often work the same stations as QRO guys. You see it all the
time in contests. Likewise guys with high radiation angle antennas do
work DX. Maybe just not always the really rare ones, or as many or as
quickly.
---------------------------------------------------------------------
It might be more interesting to discuss something like $/db to get to
closer to optimum. Going from low dipole to a higher one might cost
zero to a couple hundred and gain 3 db at about $10-$100/db. Going
from that higher dipole to something directive that picks up 4 db more
might cost a couple kilobucks - $200-500/db. Going from this
directive array to something that picks up another 3 db might cost 5
to 10 kilobucks. Now you're at > $1000/db. Diminishing returns can
happen quickly.
Desktop dB are near the cheapest. One can pickup 10 db (from 100 w)
for about $100-200/db by buying a used amp. Desktop dB can be easier
to keep "in the air" too.
--------------------------------------
So what is that extra db worth to you? Real world constrains besides
money often limit what's possible too.
Paper and electricity is cheaper than hardware. Learn how to use
EZNEC or another antenna modeling program. Spend pennies/per bad new
antenna design rather than big bucks. Go after the cheap dB first.
Debunk the myths about magic or folklore antennas that waste time and
money.
Don't forget feedline loss. One example was a local who was trying to
work satellites using 50' of RG58 feedline. Switching him over to
LMR-400 doubled his uplink radiated power and improved reception by
even more.
Read all you can. For example, K9YC's paper referenced in this thread
illustrates how difficult it is to make a vertical work as well as
even reasonable height dipole on the higher frequency bands. The
ground reflection gain of a horizontal antenna (event a zig zag one)
is hard to overcome.
73 de Brian/K3KO
On 7/15/2016 18:02 PM, Jim Brown wrote:
On Fri,7/15/2016 10:07 AM, Wes Stewart wrote:
shows an example where IONCAP says there is no (usable) path between
two stations, yet QSOs are made.
Wes,
There are exceptions to every generalization, even when the
generalization is good most of the time. I recall some well known person
who had come up poor but was no longer saying "I've been poor and I've
been rich, and rich is better." :)
Sure, there are times when a higher angle path is better than a low
angle path (or exists when the low angle path is not present). But
N6BV's statistical data for paths to various locations shows low angle
paths to be better far more often than higher angle paths. It also shows
high angle paths some smaller percentage of the time.
The HUGE problem with using the concept of "takeoff angle," and ONLY the
takeoff angle to describe and evaluate antenna performance is that by
looking at only one curve at a time, it fails to compare one antenna or
mounting height to another. Again, my work looking at the effects of
antenna height in a "flatland" QTH have all plotted the complete
vertical pattern ON THE SAME GRAPH, which clearly shows that for the
range of vertical angles where we can use the ionosphere, higher is
better! N6BV presents this quite well as a "figure of merit" for the
plots of his elevation studies in HFTA, while also showing the complete
vertical data.
73, Jim K9YC
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