[600MRG] Measuring power

[Jim Miller]

Thanks all for all the info.

I'm most likely to adapt my 67x67ft inverted L that I now use on 160.

I'll try to do some modeling on that.

73

jim ab3cv

On Sat, Mar 21, 2015 at 10:24 PM, Brian Pease <bpease2 at myfairpoint.net>
wrote:

> 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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>
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