Topband: EIRP Measurement

W2XJ w2xj at
Wed Feb 22 08:50:04 PST 2012

I would disagree. The signal measured along the ground is affected by
ground losses and is subject to ground conductivity even though the
charts show maximum gain along the ground. The signal radiated at angles
above about 10 degrees is governed by inverse distance and therefore
less loss. An attempt to determine EIRP by measurement on the ground
will be subject to local conditions thus more loss than higher angle
radiation not subject to the same attenuation. What can be assumed for
an amateur 600M installation is:

The radiator will be electrically very short.
The ground system will be far from optimum for most installations.
There will be other losses not usually found in full size MW installation

This will all contribute to more losses on the ground than in the air.

  This is different than what is shown for radiators greater than .64
wavelength where the radiating element starts to transition to being an
end fed array.

On 2/21/12 10:23 PM, Joe Subich, W4TV wrote:
>>  If it is true that the skywave is stronger than the ground wave, then
>>  the power would need to be backed off,
>  Fortunately, it is not true with short ground mounted monopole
>  antennas.  In order for the skywave to exceed the groundwave, the
>  monopole needs to be longer than half wave (somewhere in the area
>  exceeding 0.64 wave).
>  73,
>       ... Joe, W4TV
>  On 2/21/2012 8:58 PM, Rick Karlquist wrote:
>>  W2XJ wrote:
>>>  If you can find a used FIM 22 it goes from 200 KHz to 550 KHz. That said
>>>  I can not see determining EIRP by field measurement. There are just two
>>>  many variables and a degree of engineering skill not posessed by the
>>>  average amateur. The various national authorities must have a means of
>>>  measurement accessible to the average operator and is easy to enforce.
>>>  Then as I stated previously there is the interference problem. The
>>>  signal measured along the ground will be less than at higher angles.
>>>  Skywave interference will be greater because the real EIRP will be
>>>  exceeded and by a large amount in some cases.
>>  The RF ammeter test merely measures the total radiated power.
>>  It does not account for the effective signal strength at some
>>  skywave angle.  If it is true that the skywave is stronger than
>>  the ground wave, then the power would need to be backed off,
>>  but there is no way to determine how much to backoff without
>>  a helicopter field measurement.  It would depend on ground conductivity,
>>  so there would be no way to calculate it or model it accurately.
>>  Rick N6RK
>>  _______________________________________________
>>  UR RST IS ... ... ..9 QSB QSB - hw? BK
>  _______________________________________________
>  UR RST IS ... ... ..9 QSB QSB - hw? BK

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