VK4ZSS:
> yes, but then again some antennas just fall out of fashion for no
> particular good reason, hey the beverage largely dropped out of
> mainstream use for decades, then look at the flag/pennant/k9ay
> resurgence of the broadband terminated cardiod loop as an aside, does
> someone have the patent number for h.h.beverages terminated loop?, i
> would like to get a copy of the patent
We too often only seem to consider Ham use as "mainstream".
"Flags" have been used for years, as have antennas like the "K9AY
Loop". Terminated loops or arrays for daisy-chained loops called
"log-loop arrays" have been manufactured and used commercially
for many many years.
Beverages have always been popular as simple, cheap receiving
antennas where space is not a problem for years...and have
remained so over the years.
> am looking at between 10 and ultimately 30 elements. the feeder line
> will take as much effort as the antenna. i also see a gain of 20dB
> over an equal length beverage as a big plus not to mention not having
Only pattern matters.
It can't be said enough that gain is virtually meaningless for
receiving on 160 meters. Hopefully we never plan receiving arrays
based on gain.
For example, two Beverages spaced less than two hundred feet
apart broadside will show 3dB gain, yet they offer virtually no S/N
improvement.
Move the same two antennas 5/8 wl apart, and even though gain
does not change much S/N ratio improves greatly, sometimes
many dB if noise comes from a null area!
My 200 foot vertical has about 15 dB gain over an array of three
phased Beverages, yet is it a very crummy receiving antenna
compared to the Beverages. If gain worked, we'd all be using our
transmitting antennas for receiving.
Second point that can't be stressed enough...
Making arrays larger than a few wavelengths is all but useless on
160 meters because of random phase and amplitude variations over
such distances as propagation changes.
In a distance as small as 3 to 5 wavelengths, I regularly measure
180 degrees or more random phase shift on a distant signal. There
is also an amplitude problem. Levels are all over the place. At any
moment one section of the array will be gathering only noise while
the other has signal.
While both areas are ALWAYS contributing random noise, only for
very brief periods are both contributing phase-coherent signals of
reasonably close amplitudes!
The effect of making an antenna too large is an increase in fading
without an improvement in S/N! We always want to use the
smallest possible area to get the tightest pattern we can for
receiving. The practical limit on 160 seems to be about 2
wavelengths.
73, Tom
(W8JI@akorn.net)
--
FAQ on WWW: http://www.contesting.com/FAQ/topband
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|