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]
One concept when using ~3-meter, Part 15 AM transmit antennas is that the higher they are installed above the surface of Earth, the greater their signal strengths at a given distance (other things equal). The assumed reason for this is that the antenna has better “line of sight” path clearance, which reduces propagation loss.
The graphic below…[Read more]
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.
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]
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.
- All of those…
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]
Personal observations/opinions …
… about Broadcast Stations:
- The early commercial radio stations served and grew their listener base by broadcasting programs that most people wanted to listen to, even though listeners had to buy new, and relatively expensive receive systems to do that.
- Present-day commercial radio station owners are…
R.Powers & I have talked strictly and only about elevated ground-leads at a serviceable level to establish security and reachability by the operator, 9-feet at the most.
Everyone is able to promote and install whatever unlicensed transmit system they wish to.
Actually, the topic of elevated Part 15 AM antennas was first introduced in this thread by Rich Powers End80, with a post from which the clip below was taken…
“… Outdoor Part 15 transmitters which are elevated and well grounded is the standard and well established method of install. Ground mounts are something new. …”
RE: … a completely legal install could feasibly achieve over a mile radius providing the conditions (terrain, ground conductivity, ect.) are optimal.
Possibly. But other things equal, not with the coverage radius and reliability of an illegal installation such as the transmitter+3-meter whip installed on the top of a tall mast, and…[Read more]
An abundantly-confident Carl Blare wrote (in part): … Rich hasn’t shared any insight from his point of view as to why legal operators would be treated the same as pirates. … Therefore, for all of Rich’s claim of truth and accuracy his post earns the mark of incomplete.
The description of my “Part 15” setup included this: 3m Base-d…[Read more]
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