Topband: Old antennas, gain, and size

[Tom Rauch]

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