[600MRG] Measuring power

[Brian Pease]

I modeled my full-size low dipole over poor ground to get an idea of 
what power would be needed for 1W ERP, which was 100W.
Once on the air, I made a direct measurement of the max vertical field 
(off the ends) with a small calibrated loop and an ancient Rycom level 
meter.  The FCC offers equations.  It really did radiate close to 1W.

On 3/21/2015 9:04 PM, Pat Hamel wrote:
> Jin,
> Jim and other newcomers to the band with the same question,
>
> I am putting the summary paragraph here, The background comments are below.
> The bottom line is that we must show the FCC we are willing to do the
> research to follow the rules.
> For a typical ham wanting to put a vertical 600 meter antenna in the back
> yard behind the garage, it means at least reading the ARRL antenna book
> (skipping the yagi sections) and applying the mobile whip antenna sections
> to his shortened vertical. Your local library will have some older antenna
> books or order them for you. The older books have math that can be done with
> only high-school algebra.
> The modern way is to trust you built what the programmers programmed and use
> a modeling program to decide what will fit on your lot.
> -=-=-=-
> The historical way to measure power radiated (remember hams did not need to
> measure power radiated) was to follow the limitations listed on the license
> for the "kind" of station. Some "kinds" of station such as broadcast were
> required to maintain between a maximum and minimum power. How this was done
> was determined by the people who had the license and whether there was
> (rarely) on-site 24 hours a day a first-class licensee who was capable of
> measuring and certifying the correct operation.
>
> With that out of the way;
> When I was transmitting as WD2XSH/6, I used the fact that we were limited to
> maximum power output, but no minimum was required. This allowed me to use
> the tables and math the government paid to have created a LONG time ago.
> I calculated what ERP a perfect lossless antenna the size of my antenna
> would transmit, and determined the base current of the radiator for that
> power. (I used a top-loaded vertical (Inverted=L)).
> Since nothing real is perfect, I know I can show with my daily logs that I
> never exceeded the maximum radiated power.
> You may choose to emulate Dave WD2XSH/17 and use a loop antenna. Either way,
> the process is:
> Determine the radiation Resistance of the antenna you choose.
> THIS IS NOT THE "R" you will read with any real meter unless you are using a
> full-length radiator over sea water, and even then the resistance of the
> antenna wire will raise the meter reading.
>
> Then you build it.
>
> Then you measure it. If you have a 50 foot high three-fourths-inch diameter
> radiator with all the loading on top like mine, you will have a radiation
> resistance of about zero point eight ohms. You must measure it at the
> radiator base for a vertical, NOT AT THE LOADING COIL. If you have a loop,
> it is simpler.
> Mine measured about 28 ohms when the ground was dry enough to walk on.
> To get the correct current through the radiation resistance I had to drive
> it through the loss resistance also.
> -=-=-=-=-
> The bottom line is that we must show the FCC we are willing to do the
> research to follow the rules.
> For a typical ham wanting to put a vertical 600 meter antenna in the back
> yard behind the garage, it means at least reading any vintage ARRL antenna
> book (skipping the yagi sections) and applying the mobile whip antenna
> sections to his shortened vertical.
> Your local library will have some older antenna books or order them for you.
> The older books have math that can be done with only high-school algebra.
> The modern way is to trust you built what the programmers programmed and use
> a modeling program to decide what will fit on your lot.
> 73,
> Pat
>
>
>
>
>
>
> -----Original Message-----
> From: 600MRG [mailto:600mrg-bounces at w7ekb.com] On Behalf Of Jim Miller
> Sent: Saturday, March 21, 2015 7:13 PM
> To: 600mrg at w7ekb.com group
> Subject: [600MRG] Measuring power
>
> Does anyone know if the ARRL or FCC are working on a standard way for folks
> to ensure they are in compliance with what ever ERP limits are established?
> Seems like a recipe would be in order.
>
> Any news on a band for USA?
>
> 73
>
> jim ab3cv
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