A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

[rfry]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

... To get 1 mW would require improving transmitter efficiency, and increasing antenna capacitence by (for example) using a larger monopole diameter than a CB whip has.

On another website you wrote this belief related to this thread on Radio-Info, "I recently received a message addressed to me personally that claims that radiation resistance alone determines antenna efficiency, and antenna capacitance merely increases the antenna bandwidth. I've heard this opinion expressed before. Increasing the diameter of an electrically short antenna improves efficiency by reducing the loading coil inductance needed to tune the antenna to resonance."

When one differentiates between radiation resistance (Rr) and antenna system efficiency, one will find that my previously private statements to you in that message (pasted below) are true:

"That radiation resistance in ohms is related only to the height (h) of the monopole,
per this "useful approximation" from Carl Smith's 1947 I.R.E. paper Performance of
Short Antennas: Rr = h2 / 312. Therefore changing the OD of the monopole will not
change its Rr, or by itself change the efficiency of the antenna system."

Kindly note these expressions in the last sentence in the above paste, "by itself," and "antenna system."

It wasn't the change in radiator OD that improved system efficiency. It was the reduced r-f loss then possible in the loading coil used in that antenna system that was responsible for the efficiency improvement (other things equal).

 

[Ermi Roos]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

It is the efficiency of the antenna system, which comprises the monopole, the loading coil, the ground plane, and the ground screen, that matters. R. Fry's argument in the previous post does not appear to me to have any point.

 

[rfry]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

It is the efficiency of the antenna system, which comprises the monopole, the loading coil, the ground plane, and the ground screen, that matters. R. Fry's argument in the previous post does not appear to me to have any point.

The point made, and apparently accepted now by Mr Roos is that a Part 15 AM antenna system consists of more than a 3-meter conductor. Below is a clip from an earlier post of his in this thread when such a distinction was not apparent.

Of course, a 3 meter antenna is very inefficient; but radiated power is the power produced by the antenna, not the power applied to the antenna. ... The power loss in electrically short antennas is very high.

 

[Ermi Roos]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

I did not made any distinction betweeen the antenna and the antenna system. The "distinction" is only in the mind of R. Fry. The components of the so-called "system" (monopole, loading coil, ground plane, and ground screen) are all functional parts of the antenna. What is the antenna by itself--a 3-meter rod? The 3-meter rod by itself will not function as an antenna. Making a distinction between the antenna and the antenna system, as R. Fry is trying to do, is specious, and just plain silly.

 

[rfry]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

I did not made any distinction betweeen the antenna and the antenna system.

Mr Roos' posts (until recently) read as if the 3-m conductor is the Part 15 AM antenna. But it is merely the only part of the antenna system that produces useful radiation.

The amount of the applied power that does get radiated by the 3-m conductor is also a function of the losses in the complete antenna system.

 

[Tom Wells]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

I suspect we're up against semantics here..
If theres an inch of water in some places on the basement floor, is it a "flood"?

I got some heat over making a distinction in such a case last August.

R Fry is certainly pointing out the when we say antenna in this case, we really ought to be using patentspeak, wherein
we would say "AN antenna, comprised of, or consisting of, a 3 meter conductor, a feedline, a loading inductance, an earth connection , etc..."

In order to acheive best results with flea power and tiny antenna, it is essential to learn to think of all the elements
together.

He's just being a stickler to make sure everyone is informed enough to avoid the dreaded official letter that shall not
be named.

Rich, to the extent radials are supposed to return ground losses back to the radiator, aren't they functionally useful if
not actually radiating themseles?

 

[rfry]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

Rich, to the extent radials are supposed to return ground losses back to the radiator, aren't they functionally useful if not actually radiating themseles?

Yessir, they are functionally useful, and do not produce any vertically polarized, far-field radiation.

Buried radials collect the r-f currents flowing in the earth out to about 1/2-wavelength from the monopole. These earth currents are generated by the displacement currents caused by radiation from the monopole. The r-f current that flows into the antenna system feedpoint is the sum of all of the r-f earth currents flowing in the buried radials back to the system r-f ground connection at the base of the monopole.

Buried radials were discussed in greater detail in http://boards.radio-info.com/smf/index.php?topic=167593.0 .

 

[rfry]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

Mr Roos' posts (until recently) read as if the 3-m conductor is the Part 15 AM antenna. But it is merely the only part of the antenna system that produces useful radiation.

On re-reading my post clip above I see that a clarification is needed.

The 3-m conductor is the only source of useful radiation when it is mounted with its base at the surface of the earth.

But if the transmitter and 3-m conductor are installed on an elevated mount, then the entire length of all other conductors connecting to the "ground" plane of the transmitter circuits will radiate, whether or not they connect at their other end to a functional r-f ground. Even for moderate lengths they can radiate more than the 3-m monopole considered to be "the antenna."

 

[rfry]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

To find the ground loss with distance requires solving the Sommerfeld equation. The solution is difficult, and NEC can't do it, but wipl-d can.

To investigate this claim about WIPL-D, I contacted its developers by e-mail and asked if WIPL-D could model a 195-degree broadcast type monopole system using a set of 120 x 1/4-wave buried radial wires to determine the distance to the 10, 2.5 and 0.15 mV/m groundwave fields over an 8 mS/m path, for 50 kW of applied power on 760 kHz.

Those parameters were chosen because I already knew the answers provided by the FCC propagation charts. In fact I have measured that field from the system described out at the 2 mV/m contour, using a calibrated field intensity meter (FIM-41). The distance agreed very closely for those conditions with that determined by the FCC chart.

Here are clips from their responses:

WIPL-D can account reflection coefficients from infinite real ground,
but the ground is considered as flat.

This is a very difficult simulation for an exact 3DEM simulation. At
this moment, in order to get accurate result, we need to model piece
of the ground (clump) of the size where you want to calculate near
field. Even for the largest field (10 mV/m), we need piece of the
ground of size 75 km or 150 lambda. Such simulation would require
enormous number of unknowns and huge simulation time, if it would be
possible at all.

We plan to introduce so called Sommerfeld integral simulation for real
and infinite ground in one of our next releases. At this moment, we
are unable to simulate this scenario.

//

 

[Ermi Roos]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

Sommerfeld's work (1909) was for an infinite flat earth, but it was expanded about 30 years later by Kenneth Norton and others to account for the curvature of the earth. Calculated ground wave attenuation curves, based on the work of Sommerfeld, Norton, and others, that account for the curvature of the earth, have been available for several decades, and the FCC charts are undobtedly calculated, and not based on actual measurements, as R. Fry claims. Measurements have been made of actual broadcast station field strengths at various distances to test the calculated predictions, but the experimental data has a lot of scatter, and is not suitable for standard charts.

Yes, wipl-d has limitations, due to computing complexity, in dealing with finite ground conductivity, but it is not practically useless for that purpose, like NEC is.

 

[rfry]

Re: A Real-World Measurement Proving Radiation Past a Part 15 AM "Ground Lead"

Yes, wipl-d has limitations, due to computing complexity, in dealing with finite ground conductivity, but it is not practically useless for that purpose, like NEC is.

An interesting comment, in light of this previously posted e-mail response from the developers of WIPL-D to my query on this subject:

"At this moment, we are unable to simulate this scenario."

//