More on
beverage
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Basics
General info on the Beverage
How to
Get a perfect Beverage
Wires
How thick, what material?
Feed
From radio
to antenna
Ground
Ground and terminate
— here's how
Remote
Remote control of the Beverage
Views
Love letters about life with
a Beverage |
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You'll
need at least four wavelengths
By Jan E Holm, SM2EKM
Topband Antenna mail list, October
19, 2000
Nobody seems to talk about the wave angle of the beverage main lobe,
at least I havenīt seen anything.
Seems to me that anything much shorther then 4 wl doesnīt work.
If you check Misek's book you can see that you need about 4 wl for
25-30 deg waveangle and anything higher than that is useless.
In any case I have tried many many beverages and for me they donīt
perform untill they reach 1000 ft approx, all this work was done
on 80 meters, figure same would apply on 160.
By Tom Rauch, W8JI
Topband Antenna mail list, October
19, 2000
I don't follow that line of thought. Even a 1 WL Beverage has good
response along the ground for groundwave, and at low wave angles
for skywave.
A 4 WL Beverage is about useless because the phase of the arriving
wave randomly and rapidly changes in a few wavelengths of distance.
It is virtually impossible to keep two points separated by more
than 1 or 2 wavelengths "in-phase" because of the effects of propagation.
This is especially true at sunrise or sunset, when the ionosphere
is changing.
I've had 3 WL Beverages, and quickly found in A-B comparison to
shorter 1 and 1-1/2 wl Beverages they were generally worse....not
better. All my long Beverages are now long gone.
The few times the ionosphere is stable enough to allow antennas
spread over a large distance to be effective, I can combine a bunch
of smaller antennas into a large array from the operating position.
At least on 160 meters, the number of times a year I can use what
amounts to a 4 WL long array numbers in the single digits!
By Tom Rauch, W8JI
Topband Antenna mail list, October
18, 2000
Most important, the antenna with best F/B or lowest overall noise
often isn't the antenna with best ability to dig out weak signals.
Even a few minutes later, that can all change.
The problem I observe is that phase difference of arriving signals,
even in a space of only two or three wavelengths, is so unreliable
that there is now way a physically large antenna or array of antennas
can be "designed" to be optimum.
The largest practical separation that offers reasonably stable
combining of antennas is about 1 to 1-1/2 wavelengths of total spatial
area. On stable nights, away from sunrise or sunset, it's possible
to make the array larger (I can vary the number of elements phased
together) but still it requires adjustment of phase between the
various antennas.
Now imagine how likely you are to "hit" a magic combination that
works with a system you can't adjust, like a 1500 foot Beverage!
Sure, you'll find a time and distance where the antenna works better
than a shorter antenna...but you'll also find just as many times
when it won't work as well as a shorter (1 to 1-1/2 wl area) antenna!
A very large array won't work as well as predicted because
phase of the signal won't be stable over the area of the array.
Phase can be as much as 180 degrees out one time and back in phase
at other times, and it can change from moment to moment on some
nights!
We need to be able to determine a directivity factor, and understand
that if the array is physically large (more than 1 or 2 wavelengths)
the signal arriving at all parts of the array won't allow us to
achieve the performance we estimate.
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