[600MRG] ERP, EIRP, How & Why

[Edward R Cole]

Pat,

Sounds right to me.  I determined R+jX from a model in 
EZNec.   R=0.83 and measured R with my modified MFJ analyzer as 
18-ohms.  Po=100w resulted in TPR= 4.61w  EZNec indicated gain of 
1.48 (1.7 dBi) giving EIRP=1.48*4.61 =  6.8w.  ERP = EIRP/1.64 = 4.15w.

Only variance with Rudy's calculation is he adds 3-dB gain for dipole 
over perfect ground.

My antenna is base loaded inverted-L: 43x122 feet.

73, Ed - KL7UW

At 06:23 AM 1/28/2015, Pat Hamel wrote:
>There are historical reasons why the radio regulatory situation exists.
>
>The radio industry worldwide has always had politically set limits on the
>transmitted power.
>The experimental service (FCC Part-5) was intended originally to allow
>manufacturers to legally transmit to verify performance required by their
>customers or the FCC.
>Commercial stations generally have a maximum and minimum power level,
>During a yearly required "proof of performance" LF & MF stations were
>required to show they met the license requirements.
>The way that the power was measured at startup of a new station was by
>paying a professional engineering company to study maps and determine the
>signal strength at certain locations and then measure to be sure that the
>calculated conditions were met. From then on, for a non-directional AM
>broadcaster, the originally determined local meter readings were the way to
>insure the conditions continued to be met.
>The regulations always required the results to be kept and filed with the
>FCC.
>Hams were exempt as were the experimental stations.
>
>Years ago, the government paid to have experiments performed on transmitting
>antennas. The results were the same for antennas of the same electrical
>length (repeat Electrical length).
>The results of these experiments are that the performance of any antenna
>over perfect ground and/or in the clear (based on antenna type) can be
>predicted mathematically.
>The antenna modeling programs use this mathematical foundation to do their
>work.
>
>A convenient way to explain the efficiency of an antenna was adopted - known
>as the radiation resistance.
>The radiation resistance of an antenna is the value of a resistor that would
>dissipate as much power as the antenna radiated.
>In a perfect antenna, the radiation resistance and measured "R" (of R+Jx)
>would be the same, but that can't happen.
>
>
>We all know that physical length can be measured in meters or feet.
>Radiated power can be measured in effective radiated power (ERP) or
>Isotropic effective radiated power (IERP).
>
>Most real antennas exist in real spaces, with trees, bad (lossy) soil,
>sheds, houses, roads, railroad tracks, and people changing things.
>This reality leads to the logical conclusion that a real antenna must be
>less efficient than the ideal calculated antenna.
>
>For example the 600 meter band 50 foot high antenna at WD2XSH/6 calculated
>to have Zero.Point Seven Seven ohms radiation resistance.
>The measured input "R" was in the vicinity of 28 ohms. 0.77 / 27.33 =
>efficiency of 2.8 %.
>This quick ratio calculation shows that less than three percent of the power
>from the transmitter would be transmitted - only if the antenna was perfect.
>
>The antenna was supported by a tree which had sap alive almost all year and
>the neighbors would not allow lawns to be torn up to lay long radials, so it
>is logical that limiting transmit power to that which would be legal in a
>perfect antenna must also be legal in the real case.
>I know of no experimental stations who have been visited and examined by the
>FCC, but I have my notebook with all the printouts from our coordinator, my
>measurements and calculations, and my logs.
>My four 811's loafing along at 30% efficiency class "B" linear caused no
>interference and made 15 watts ERP from the antenna regularly.
>
>The question posed on the reflector was anticipating FCC granting a new ham
>band at 630 meters.
>The FCC has traditionally chosen ERP measurements.
>Until they decide LF & MF ham allocations, we experimenters are limited to
>the conditions specified in our licenses.
>
>Use the method of determining your power that applies.
>Forward this to anyone who may be interested, but (disclaimer) my 74 year
>old brain makes mis-teaks.
>Pat W5THT & WD2XSH/6
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73, Ed - KL7UW
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