[600MRG] Measuring power

[Pat Hamel]

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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