Hm. That means that you can't run more than about 16-20 watts to an
ordinary dipole, since a dipole over ground produces a field strength
that's typically 4-5 dB greater than a dipole in free space. See, for
example, the EZNEC example BYDipole.EZ, which shows a field strength of
6.82 dBi, or about 4.7 dB greater than a free space dipole.

Roy Lewallen, W7EL

Greg Queen wrote:
Cecil,

I am no expert on the "legalese", but it appears the FCC has specified power
in terms of Effective Radiated Power (ERP). The standard is no more than
50-watts radiated by a dipole in free space. My interpretation is that you
look at the performance of your antenna at its maximum radiation point
(i.e., the azimuth & elevation) and compare it to the radiation from a
dipole in free space at its maximum radiation point(s). If your antenna has
less radiated power than the dipole, then you can feed more power to the
antenna (up to the point that you get the same radiation as a dipole in free
space).

I think this is the first time the FCC has used ERP (which includes antenna
gain and feedline loss) as a power specification for amateur radio.

Greg Queen
AE6MF

Greg Queen wrote:
I am no expert on the "legalese", but it appears the FCC has specified power
in terms of Effective Radiated Power (ERP). The standard is no more than
50-watts radiated by a dipole in free space. My interpretation is that you
look at the performance of your antenna at its maximum radiation point
(i.e., the azimuth & elevation) and compare it to the radiation from a
dipole in free space at its maximum radiation point(s). If your antenna has
less radiated power than the dipole, then you can feed more power to the
antenna (up to the point that you get the same radiation as a dipole in free
space).

But a horizontal dipole over ground has a gain over a dipole in free space.
Consider a horizontal dipole with a maximum gain of 6 dBi Vs a free space
dipole with a maximum gain of 2.14 dBi. Do you have to decrease the power
to the horizontal dipole over ground to bring it down to 2.14 dBi?

Consider a vertical dipole with a maximum gain of 0 dBi. Can the power
be increased to obtain the free space 2.14 dBi or 6 dBi over ground?
--
73, Cecil http://www.qsl.net/w5dxp



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From: Roy W7EL wrote
Hm. That means that you can't run more than about 16-20 watts to a n
ordinary dipole, since a dipole over ground produces a field strength
that's typically 4-5 dB greater than a dipole in free space.

Roy, the FCC has clarified this issue recently in communications with ARRL. The
FCC indicated we should do all our compliance calculations for 5MHz as if the
antennas are in free space.
That certainly makes it a lot easier, doesn't it?

Bonnie KQ6XA

Greg Queen wrote:
I am no expert on the "legalese", but it appears
the FCC has specified power in terms of Effective
Radiated Power (ERP). The standard is no more than
50-watts radiated by a dipole in free space.

% Bonnie KQ6XA (in a slightly different thread):
% Roy, the FCC has clarified this issue recently
% in communications with ARRL. The FCC indicated
% we should do all our compliance calculations
% for 5MHz as if the antennas are in free space.

Cecil, W5DXP:
Consider a vertical dipole with a maximum gain of
0 dBi. Can the power be increased to obtain the
free space 2.14 dBi or 6 dBi over ground?

Don't ask.
Don't tell.
Don't pursue.

K7JEB

K7JEB wrote:
Don't ask. Don't tell. Don't pursue.

Darn, I was about to lay down a perfect ground for my dipole
but EZNEC says that would only gain me 1.5 dB over normal
ground.

Wonder how many 5 MHz hams have already violated the FCC
guidelines by running 50 watts into a dipole over ground?
Oops, that's asking and pursuing, isn't it?
--
73, Cecil, W5DXP

Thanks for the info. It sure does make it easier. Grounded antennas like
a ground mounted vertical or inverted L could be modeled by removing
ground and adding a mirror image in free space, or by using perfect
ground and subtracting 3 dB from the resulting field.

Roy Lewallen, W7EL

Expeditionradio wrote:
From: Roy W7EL wrote
Hm. That means that you can't run more than about 16-20 watts to a n
ordinary dipole, since a dipole over ground produces a field strength
that's typically 4-5 dB greater than a dipole in free space.


Roy, the FCC has clarified this issue recently in communications with ARRL. The
FCC indicated we should do all our compliance calculations for 5MHz as if the
antennas are in free space.
That certainly makes it a lot easier, doesn't it?

Bonnie KQ6XA