Re: LF: ERP<>EMRP

[Rik Strobbe <rik.strobbe@fys.kuleuven.be>]

Andy, Stefan,

the theoretical values are:
isotropic antenna: 0dBi / -2.15dBd (directivity = 1)
half wave dipole: 2.15dBi / 0dBd (directivity = 1.64)
short dipole: 1.76dBi / -0.39dBd (directivity = 1.5)
quarter wave vertical monopole: 5.16dBi / 3dBd (directivity 3.28)
short vertical monopole: 4.77dBi / 2.64dBd (directivity 3)
This values assume free space for the dipoles and a perfect (conductive)
ground plane for the monopoles. And no losses (greenery, buildings).
For a certain area in north-east England these values are +/-
100dB

For calculating the (theoretical) EIRP one need to take the dBi values or
the directivity
For calculating the (theoretical) ERP one need to take the dBd values or
divide the directivity by 1.64 (there comes Stefan's 1.83 = 3/1.64)
For calculating the (theoretical) EMRP the reference is a short monopole,
one need to take the dBi-4.77 or dBd-2.62 values or divide the
directivity by 3.

So EIRP gives the "best" values, that's why manufacturers of
inferior antennas often give dBi values on their prospects but mention
just dB ;-)
An easy way to add a good 2dB to the gain.

73, Rik  ON7YD

At 09:32 22/01/2010, you wrote:

Well, yes it is I suppose if you lump antenna directivity into the equation. 
I^2.R is the actual power radiated.
Which direction it then goes is a different issue.
 
Anyway, what is the true directivity figure to use for a monopole ?
A very short dipole has 1.5 times directivity.  Therefore a short monopole over perfect ground ought to have 3 times.  Neither of which is 1.83

Andy
www.g4jnt.com

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2010/1/21 Stefan Schäfer < schaefer@hst.tu-darmstadt.de>

Hi Andy,

Isn't it, the ERP is I^2*Rrad*1,83, if we assume a vertical antenna?

73, Stefan

________________________________

Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von Andy Talbot

Gesendet: Do 21.01.2010 20:27

An: rsgb_lf_group@blacksheep.org

Betreff: Re: LF: Re: M0BMU - any chance of some new ERP estimates please?

So go on:  argue against the Rrad (an exact figure derived from basic electromag theory) and Rloss (easily measurable, called Ohms law) way of getting antenna efficiency.

Or  ERP =   I^2 . Rrad   where I is measurable.

Only uncertainty in any of these techniques is the effective height of the antenna used to get Rrad, but absolute worst case, can only ever lead to 6dB error.  The difference between no top hat and an infinite top hat

Andy

www.g4jnt.com < http://www.g4jnt.com/>