Topband: EIRP Measurement

W2XJ w2xj at
Tue Feb 21 15:56:06 PST 2012

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.

I could see where if there were a sufficient market a device that was
sort of a combination of a vector impedance meter and an ammeter could
calculate EIRP on the fly. It would have to be located remotely at the
antenna feed.

On 2/21/12 5:22 PM, Jack/W6NF wrote:
>  On 2/21/2012 11:51 AM, W2XJ wrote:
>>  The Potomac Analog FIM is no longer available, nor are the parts to
>>  repair them and calibration service is no longer available. The new
>>  meters are expensive digital units. But in broadcast we do not use them
>>  to determine power but rather coverage usually when directional systems
>>  are tuned.
>>  On 2/21/12 1:05 PM, Jack/W6NF wrote:
>>>  On 2/21/2012 8:26 AM, Joe Subich, W4TV wrote:
>>>>       >      On Mon, 2012-02-20 at 19:04 -0700, Tod - ID wrote:
>>>>       >
>>>>       >      The important thing is to have a way to assure that when someone
>>>>       >      measured the same field at the same point with the same type of
>>>>       >      measurement device they would get the same measurement result.
>>>>       >      That would allow us to compare measurements between different
>>>>       >      people even if we did not know the absolute field strength value.
>>>>  I think simple, repeatable and accurate are a difficult triad.  What
>>>>  you are talking about is an accurate Field Intensity Meter (FIM) and
>>>>  getting stable calibrations with home constructed equipment is not
>>>>  going to be easy - let along easy to duplicate.  The closest solution
>>>>  is to use standard antennas (not simple whips) and calibrate them
>>>>  against broadcast signals at known locations and known field strengths.
>>>>  This will still require separate antennas for 160 and 630 meters and
>>>>  separate calibration sources on the appropriate ends of the standard
>>>>  broadcast band (due to the antennas).
>>>>  73,
>>>>          ... Joe, W4TV
>>>>  _______________________________________________
>>>>  UR RST IS ... ... ..9 QSB QSB - hw? BK
>>>  It's been many years since I have had to make any AM broadcast field
>>>  measurements. I don't recall if the Potomac Instruments, or other, FIMs
>>>  go much below 550kHz.
>>>  73,
>>  _______________________________________________
>>  UR RST IS ... ... ..9 QSB QSB - hw? BK
>  Yes, I am aware of that, having been CE at several DAs, including one
>  critical night-time array.  I was thinking that, if the FIMs covered the
>  necessary frequencies, EIRP could be inferred by measuring field strength.
>  I'd still be curious if any of the new FIMs have extended coverage that
>  would make them useful.
>  Oops, I guess this is now OT, right? ;>)

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