[600MRG] ERP, EIRP, How & Why

[Marshall Cross]

NEC-4.2 will calculate a power gain (product of the directivity gain and efficiency) for the space wave case only. For the surface wave component of the ground wave it does not return a value for power gain (dBi), rather the peak E and H field strength values. 73, Marshall, W1HK, #41   

-----Original Message-----
From: 600MRG [mailto:600mrg-bounces at w7ekb.com] On Behalf Of Kenneth G. Gordon
Sent: Wednesday, January 28, 2015 1:25 PM
To: 600MRG
Subject: Re: [600MRG] ERP, EIRP, How & Why

On 28 Jan 2015 at 8:57, Edward R Cole wrote:

> Ken,
> 
> Don't confuse antenna efficiency with gain.

I'm not.

>  Kraus (Antennas) defines
> antenna gain as directivity.

Of course: no antenna can output more total RF than is impressed on it. One can only "point" more or less of that RF in some particular direction or directions, and less of it in others. This is what we call "gain"...which it really isn't. "Gain" with regard to antennas is certainly a handy word to describe what is actually happening, but many (most?) hams misunderstand what is actually taking place.

>  The inverted-L radiates less upward
> than horizontally (as most vertical antennas do), thus a mild bit of 
> directivity.  Rudy shows nearly the same amount in his calculations
> (1.7 dB).  But coupled with 4.6% efficiency it will not radiate 
> anywhere near a full-size quarter wave vertical.  This gain was 
> derived from EZNec.

Well, EZNec is a handy tool (as is MMANA GAL, which I use) but it most certainly is only an approximation at best. It is a model. Those programs can give us a good idea of what is happening, but none can exactly describe what is actually taking place, either.

> How did you arrive at your -2 dB gain?  At what frequency?

The antenna was designed specifically for 80 and 40 meters. At 80 meters, it shows a "gain" of MINUS approximately 2 dB over a resonant dipole according to every reference I could find on the subject.

I am also using a version of VOACAP. In that collection of programs, one of those is a way to input your own personal antenna parameters to the main program in order for it to provide more accurate point-to-point propagation data.

THAT also shows my antenna as having approximately MINUS 2dB "gain" 
over a dipole. The actual figure, as I remember it,. is very close to 1.87 dB...minus.

Lastly, my experience with the antenna over the past 10 years pretty much bears this out.

Ken W7EKB

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