[CW] OT: Antenna Radiation Efficiency

[Richard Knoppow]

    Antenna efficiency is a can of worms. The idea is that the power 
absorbed by the antenna should be radiated into space. The impedance of 
the antenna is not a good indicator of this. The antenna may read the 
expected impedance when all the power is being absorbed by something. 
For instance a dummy antenna can have ideal impedance but is not 
radiating anything (if its correctly designed). I agree with you about 
keeping the antenna and its feeders away from anything conductive or 
absorptive. I would think much more than a foot, at least up to HF. Does 
not apply to non-radiating feeders like coax since they will not couple 
into nearby objects. Note that moving an antenna will certainly affect 
its impedance but that does not necessarily indicate its radiation 
efficiency since it does not tell you where the power is going. All 
power going to an antenna is either radiated or absorbed, you want to 
minimize the absorption.
    Probably the biggest enemy of antennas is trees. No trees within at 
least the "near zone" or something like a couple of wavelengths. Ground 
conductivity is very important. If you can't get a good ground you need 
a proper ground plane. I think, but am not sure, a balanced vertical 
antenna can operate without a ground system. In fact there are broadcast 
antennas made this way, center fed vertical radiators without a ground 
system. An antenna like this can be quite good at radiating power.
    The directional properties are also very important. For distance a 
low angle of radiation and minimum higher angle lobes are important.
    The truth is that the conditions necessary for efficient antennas 
are hard to come by for amateurs. Transmitting and receiving antennas 
are reciprocal, same requirements for both but transmitting antennas 
must have sufficient power handling capability.
    There are tons of literature on antenna design, much of it beyond 
me, gets very mathematical.


On 7/30/2024 5:07 PM, D.J.J. Ring, Jr. wrote:
> Concerning antenna radiation efficiency.
> 
> I only have the suggestion that I learned a long time ago, but 
> unfortunately I don't have any scientific measurements to confirm it. It 
> very well may be my superstition but here it is. It's simple enough to 
> try but exhausting to try to measure and confirm.
> 
> N1EA Antenna Rule #1:
> 
> No part of the antenna shall touch or be within one foot (305 mm) of any 
> object conducting or non-conducting including leaves or tree branches 
> including antenna supports. For antenna supports I made a one foot 
> separation from the end of the antenna insulator at the end of the wire 
> antenna and the antenna support (building, tree, tower or PVC pipe) made 
> from Kevlar rope. Kevlar rope is my choice as it's thin diameter but 
> quite strong.
> 
> My friend and inventer Michael Laronda, WA1OMI measured using 
> instruments the impedance of the antenna while we moved the antenna away 
> from objects when the impedance of the antenna no longer changed, we 
> noted that when separation distance in all cases for conductors and most 
> surprisingly non-conductors was equal or greater than one foot all 
> interactions with the antenna stopped. Antennas that previously only 
> performed poorly then performed much better. As I said, only the 
> measurement of how much separation was needed to have the antenna no 
> longer be effected by mutual impedance was repeated and carefully 
> measured. The efficiency improvements were very significant but our 
> notes have been lost long ago, but we just made it a design parameter 
> that no conductor or non conductor be within one foot (305 mm) of any 
> antenna except non-conducting support ropes which were tied to the 
> antenna end insulators. Branches and vegetation were just cut away.
> 
> 73
> 
> David Ring N1EA


-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998