[TowerTalk] Antenna Gain and Reality

[Roger (K8RI) on TT]

As I see it:
There are several absolutes in antenna gain and many probably, might, 
maybe, could be attributes.

The two absolutes are the 2.1 db dipole to Isotropic source (I've been a 
ham since 61 and the books have always listed that figure) and gain 
measurements are only true for the test range where they were made.  
Hence even though the manufacturer may be honest and make an honest 
attempt at measuring gain figures in all axises, comparing one 
manufacturers antennas against another manufacturers antennas from 
advertized data only gives ball park figures and tells me little about 
how they will perform in my installation.

Doubling the number of antennas theoretically doubles the gain which is 
an additional 3 db for each doubling although it's unlikely due to 
losses in feeding and matching that this will be achieved. Losses in the 
additional coax can be substantial.

Even with computer modeling of the installation, the inputs must be 
accurate and few if any know the ground characteristics near or far to 
any great precision.

The radiation pattern at vertical angles is a crap shoot.  You are 
playing the percentages for atmospheric conditions that will match the 
maximum signal radiated will be at the most desirable angle to match 
those conditions.  That's why the contesters have stacks that allow them 
to select the antenna height that lets them put the maximum signal into 
the desired range/distance.

As most of us have both budget and land constraints that limit us to the 
number, size, and height of our antenna(s) It's unlikely we can depend 
on equaling the performance in the advertized figures.  Often for 40, 
75, and 160, a simple wire antenna, or vertical will out perform all but 
the largest and/or sophisticated antenna or array.

I've had extremely good luck with sloping, center fed, half wave 
dipoles.  compared to some stations running Yagi antennas at reasonable 
heights. Many times the first word in the response to my call, is 
"Wow".  Yes, I do run QRO, but the best sounding signal out of my 
tetrode amp is at, or around the legal limit so there is little 
incentive for pushing beyond the legal limit for that extra 1 db and 
those tubes are expensive.

-- 

73

Roger (K8RI)


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