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]
RE: I’ve never come across a single indication found in any published documentation … or for that matter in any technical calculations that 15.219 achieved greater distances than about a mile.
NEC4.2 shows that a 3m Base-driven Whip+Tx @ 10m AGL, 10m Lead from Tx to Ground Rod, 100 mW d-c input to Final RF Amplifier, 65 mW PA RF Output Powe…[Read more]
Example of “Obstruction Loss” to a MW AM Signal
Q: What loss of field intensity does a single private home cause to the groundwave propagation of a MW AM signal?
A: The signal strengths shown on a Tecsun PL-880 receiver tuned to a 500W AM broadcast station located 55 miles from the receiver location were …
Outside the east wall: 37 dB…[Read more]
Below is a graphic showing how that condition can be true.
Examine the region between 50 and 100 meters from the transmit antenna of a “Part 15” AM station (distance is plotted along the horizontal scale of the graph).
The total field intensity along the horizontal plane is shown by the topmost line plotted on the graph, and references the…[Read more]
My last post didn’t say or imply that all obstructions have loss, just described how any loss that might exist in an obstruction would affect a weak or strong e-m wave while it was passing through that obstruction.
Even though a signal may be weak within an obstruction such as a building, the field usually recovers to the same strength beyond the…[Read more]
RE: But the conclusion is the same: higher field strengths can penetrate obstructions which weaker field strengths cannot.
What do you think about this explanation?
- For a given set of propagation conditions, obstruction loss in percent of transmission and/or decibels of loss is the same for all e-m field intensities, regardless of the…
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