Rich

A “heads up” observation:  historically the FCC has inspected the installed transmit systems of the operators of AM and FM transmitter and antenna hardware that had been tested by an FCC-approved compliance lab and FCC-certified under Part 15, and went on to cite their operators when those installations/operations did not meet the applicable…[Read more]

Observation:  it doesn’t include a receive antenna with a known pattern/gain across its operating range.  Therefore it can’t accurately measure the absolute value of the field intensity or power of signals arriving at that receive antenna.

From Boomer’s post above:

“The _nighttime signal_ can reach as far west as Minneapolis and Winnipeg, and as far south as New Orleans.”

This sentence from the Wikipedia text quoted above is accurate, but it doesn’t apply to their daytime groundwave coverage area — which is close to what is shown on the map I posted.

CZFM operates on one of the f…[Read more]

RE:  “Do you know that AM 740 (zoomer radio) from Toronto has the most coverage of any station in North America, not only covering all of Ontario from Windsor to Kingston and north to Parry Sound and North Bay, but 28 states also? That’s all of central North America! That’s in the daytime!”

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Sorry, but the useful _day…[Read more]

RE: … tell us if a FI increase equals a linear increase in expected range …

It does, for propagation environments having equal characteristics  — as long as…

» the ambient noise and interference present on/near that carrier frequency is the same at all receive locations, and

» the same receive hardware and operational configuration is u…[Read more]

Sorry, but No, that table doesn’t convert the values of dBµ shown on the display of some Ultralight receivers to the field intensity arriving at the antennas of those receivers.

The units of measure for the numbers in the table are related to power, not field intensity.

RE:  Not sure if everyone has seen the distance chart that Ramsey use to post if you used the 250uv@3meters. …  I hope this will help out with distance under part 15.239 and 250uv@3meters.  These are expected field strengths at these measured distances.

A caveat:  that table shows the fields that would exist in free space.  However the fiel…[Read more]

With a perfect impedance match between the coax and the load at its far end, the current flowing on the OD of the inner conductor is equal to the current flowing on the ID of the outer conductor, but they are 180 degrees out of phase.  Therefore their radiated fields cancel.

But when the current on the ID of the outer conductor reaches the far…[Read more]

Below is a graphic showing how r-f current can flow on the outer surface of the outer conductor of a coaxial cable.

This occurs even when the termination at the far of that coax exactly equals the characteristic of the coax connected there (often 50 +j 0 ohms).

That current flowing along the outer surface of the coax outer conductor produces e-m…[Read more]

Below is a link to important information about why and how coaxial cables produce e-m radiation into space.

https://www.w8ji.com/common_mode_current.htm

Earlier today I posted a reply to this thread, then made a small edit to it after it posted.  I got a message saying that I already posted this, and it was a duplicate.  In that process it did not post my edited version, and it removed the original version.

Here is the final version as a graphic image.

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John M. — I did not attempt to model the system you (apparently) are thinking of installing.

In fact, your description of it didn’t appear here until AFTER I posted my graphics.

If you are not installing the system I modeled, then of course your setup will not produce the results shown for the system I modeled.

My model of the system with the…[Read more]

What does matter is whether or not an FCC equipment certification overrides an FCC Rule applicable to that equipment.

Below are two graphics from NEC4.2 to help understand and compare the performance of two AM transmit system configurations, for the ~similar operating conditions shown for them.

The first one shows the performance with an antenna system having a total radiating length of approximately 3 meters.

The second one shows a system using a remote…[Read more]

RE:  I’m sure that the NEC software is for those garbage Emerson or Sound design Radios …

NEC software analyzes the e-m fields radiated/received by an antenna system, including other conductors in the propagation environment if they are included in the model.

NEC software does not model the performance of receivers, or of complete tr…[Read more]

RE: “… the internal tuner is switched out of the circuit when the external (final stage of the transmitter) is employed. …”

And that is the configuration of my NEC model.

Also, suggestions have been posted elsewhere that the antenna+ATU should be mounted at least 20 feet above ground level.

For thought and discussion, below is a NEC4.2 analysis of the AM transmit system described there.  The remote ATU is located at the upper end of the 25-ft coaxial cable, at the feedpoint.

The red lines along the conductors of that system show the relative distribution of r-f current along those conductors.

Observations:

• All of those…

[Read more]

ArtisanRadio wrote:  My comments were directed towards those who claim to know the precise meaning of the FCC rules (most especially 15.219), when the FCC themselves have enforced those rules inconsistently over the years.  …

AR probably includes me in the quote above, however I have never posted that I know the precise meaning of the FCC R…[Read more]

ArtisanRadio wrote: “The FCC has (almost) always based their decisions on reasons other than physical principles.”

The early technical decisions for AM/FM/TV broadcasting such as the transmitter power, frequency, transmitter site location, required antenna efficiency, and permitted radiation pattern were made by the FCC with due respect to the…[Read more]