On Thu, 16 Jun 2005 16:56:41 GMT, "Jer"
wrote:

At any rate, if I knew more about my antennas characteristics I might could
figure out the band/end location where it would be loudest at any given
time. Is this all wet, and TOA wouldn't help in that at all?


The TOA will help in any QSO. A low TOA will tend to open you up to
DX QRM such as on 40 meters, but an NVIS with near vertical TOA will
manage more regional communications than DX. You might not even be
bothered by the 500kw SW station in Germany. Of course, the station
you talk to will also have to deal with that station.

Knowing the TOA is as beneficial as knowing where the nuls are on your
beam.




--
73 for now
Buck
N4PGW

Jer wrote:
Wouldn't this 'gain' be useful in figuring out just where you could dump
your maximum signal somewhere in the world? It might not be where you
want, but at least you might have an idea of where you would stick a loud
signal using max gain at some elevation angle? Or is this a totally useless
idea? I don't pretend to know what I'm talking about here, but it seems
logical that by using this type of data it would help you figure out where
you were going to put in a stronger signal.

Shields up!

No, I don't think it's a useless idea, just one that hadn't occurred to
me. It will indeed tell you where your signal will be strong, assuming
that propagation is supported in that azimuth direction and at that
elevation angle.

Roy Lewallen, W7EL

Jer wrote:
I'm another Ham that could care less about DX! I just want to use the
proper frequency depending on the time of day/night to communicate with some
friends located around the west coast. Very few DX stations will hold a rag
chew, just slam bam, thank you mam, i.e. 599 OM !... ugh..

At any rate, if I knew more about my antennas characteristics I might could
figure out the band/end location where it would be loudest at any given
time. Is this all wet, and TOA wouldn't help in that at all?

The TOA isn't the way to get that information. What you need to do is,
first, find out what elevation angle will be used for communication on
each band at the time(s) of day of interest. Again, something like
W6ELProp is good for doing that. Second, since you're interested in
having the strongest signal, look at the signal strength reported by
W6ELProp or other propagation program at each of those times. Next, use
EZNEC to look at the gain of your antenna at the elevation angles you
found with the propagation program. Finally, add the antenna gain to the
signal strength reported by the propagation program at each band and
time. The largest number will give you the best signal. This of course
comes with the caution that propagation prediction is generally much
less accurate than antenna pattern calculation, so there can be a lot of
variability in the accuracy of the results.

I think that if you go through this exercise a few times, you won't find
much correlation between your results and the TOA.

Roy Lewallen, W7EL

Buck wrote:

The TOA will help in any QSO. A low TOA will tend to open you up to
DX QRM such as on 40 meters, but an NVIS with near vertical TOA will
manage more regional communications than DX. You might not even be
bothered by the 500kw SW station in Germany. Of course, the station
you talk to will also have to deal with that station.

Knowing the TOA is as beneficial as knowing where the nuls are on your
beam.


That's a good and perfectly valid point. Knowing the TOA would be useful
in determining what range of distances you're most likely to encounter
QRM from.

Roy Lewallen, W7EL

Roy Lewallen wrote:

The elevation
angle at which the gain is maximum is of very little practical use --
EZNEC reports it only because a lot of people wanted it (for reasons
which remain mysterious to me).

Maybe the guys out at Goldstone can explain it.

:-)
ac6xg

On Thu, 16 Jun 2005 10:41:19 -0700, Roy Lewallen
wrote:

Buck wrote:

The TOA will help in any QSO. A low TOA will tend to open you up to
DX QRM such as on 40 meters, but an NVIS with near vertical TOA will
manage more regional communications than DX. You might not even be
bothered by the 500kw SW station in Germany. Of course, the station
you talk to will also have to deal with that station.

Knowing the TOA is as beneficial as knowing where the nuls are on your
beam.


That's a good and perfectly valid point. Knowing the TOA would be useful
in determining what range of distances you're most likely to encounter
QRM from.

Roy Lewallen, W7EL

Or what antenna to choose to avoid it.

--
73 for now
Buck
N4PGW

On Thu, 16 Jun 2005 10:38:18 -0700, Roy Lewallen
wrote:

Jer wrote:

I think that if you go through this exercise a few times, you won't find
much correlation between your results and the TOA.

Roy Lewallen, W7EL

Of course, he could just check to see which antenna hears the station
the best with the least QRM.

From what I understand, the TOA of a DX station changes over time. It
may come in at a low angle and then rise a bit or visa versa. Or it
may never get high enough for a particular antenna

--
73 for now
Buck
N4PGW

Buck wrote:
When I setup an antenna in EZNEC, I want to see the azimuth but the
program asks for an elevation angle. WHat angle should I use? I have
been randomly using 5 or 10 deg.


An example of an approach to antenna design that starts with
identification of the paths to be optimised is at
http://www.vk1od.net/7MDipole/7MDipole.htm .

In this case, I was interested in local contacts and over 50% of
Australia's population was located in just four cities at distances up
to 1000Km. The propagation paths to those locations was modeled to
provide the geometry for assessment of antennas in EzNEC.

BTW, 5 to 10 degrees elevation is probably below most propagation paths
for DX, let alone local contacts. Lowest angle doesn't necessarily
translate to optimal for distant stations (it depends on the propagation
mechanism at the time), and the most desirable DX might not be at the
greatest distance. Best performance at low angles might assure maximum
pickup of local noise sources, and in my case QRM because I am not at
all interested in DX.


Owen

Owen wrote:

BTW, 5 to 10 degrees elevation is probably below most propagation paths
for DX, let alone local contacts. Lowest angle doesn't necessarily
translate to optimal for distant stations (it depends on the
propagation mechanism at the time), and the most desirable DX might not
be at the greatest distance. Best performance at low angles might
assure maximum pickup of local noise sources, and in my case QRM
because I am not at all interested in DX.

Recent editions of the ARRL Antenna Book cover this topic very
thoroughly. They note that arrival angles from a given location vary
with time of day, time of year, time in the sunspot cycle, whether the
ionosphere is stable or disturbed, and so on...

Then they produce statistics for major paths (eg "G-VK"), averaged over
all these factors. OK, so these figues are "only computed"... but they
are computed using VOACAP (the Voice of America's propagation program
that has has years of development and a lot of verification) so this is
the best information we're ever likely to get.

The big lesson is that there is ALWAYS A SPREAD OF POSSIBLE ANGLES.

As Owen says, 5-10deg is not always the most likely angle. It all
depends on how many F2/F1/E hops will fit into the required path length.
That means the arrival angles tend to jump, especially as the band is
coming on or going out. (However, it turns out that a substantial
fraction of signals on the G-VK path come in at angles of only a degree
or two. These paths are workable, of course, but the antennas at both
ends will usually have very little gain unless the land slopes down to
lower the reflection angle.)

Hams became fixated on "5 to 10 degrees" a very long time ago, and we
still tend to wave this figure around like some kind of flash-card.
Professionals have moved on to a much better understanding of the range
of possible angles that they need, and this is now starting to filter
into ham radio too.

If anyone is interested in this subject and hasn't read a recent edition
of the ARRL Antenna Book, it's time for an update.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek