There has been some online comment to the effect that commercially-produced Part 15 AM transmitters with internal loading coils typically cannot impedance-match the transmitter to antenna systems with radiating lengths longer than about 3 meters.
Clarifications/comments about this:
- Typical radiating conductors of Part 15 AM antenna systems…
RE: It is what NEC does with Part 15 level signals, and their application in the real world (not a dream world, full of simplifying assumptions) that is in question. That does NOT include ignoring obstructions, as most of your posted simulations and results do. I note that you do not answer my question as to whether NEC can model obstructions,…[Read more]
RE: … It states right in the documentation that if the model is bad, then the results will be inaccurate. If the assumptions don’t map to the real world, then the results will be inaccurate. …
There is no doubt about that: garbage in = garbage out.
However many software implementations using NEC code (including the one I use) include test…[Read more]
radio8z wrote, “Rich, is the change in slope on the graph at D = 30 meters due to the transition out of the near field into the far field? … “
Yes, it is.
Your comments about the coverage of your Part 15 AM setup are interesting, and do agree pretty well with my NEC4.2 evaluation of a similar system.
The experience suggesting that elevated…[Read more]
RE: “These formulas are designed for higher power transmitters, not part 15. For example my part 15 has no loading coil. The efficiency is higher then he mentions. So his calculations are not that useful I think”
My public, quotable comments to that above text clip are:
1.) The formulas contained in the NEC4.2 software used to create the data f…[Read more]
RE: And your point is … ?
What led to that result?
I attempted to re-post it just after it went missing, but that was not permitted by the Part15.org website at that time.
I’ll try again in a few minutes, in a new topic thread titled “Part 15 AM Systems vs. NEC Software Analysis”
‘These formulas are designed for higher power transmitters, not part 15. For example my part 15 has no loading coil. The efficiency is higher then he mentions. So his calculations are not that useful I think”
From End 80: Like I said, I don’t understand your charts most of the time anyway, but I’m interested to her your response on this.
RE: … The actual hypothesis is that adding obstructions will change that graph significantly (i.e., it doesn’t address the effect of elevation along an obstructed path). …
The following two graphics were posted on Part15.org several weeks ago,* and show the measured results when a tall, steel-reinforced building, or natural terrain ele…[Read more]
My post at https://part15.org/forums/topic/fields-radiated-by-an-elevated-pt15-am-dipole/#post-110101 is appropriate in this thread, as well.
I posted it with a new thread title to make it easier to search for (and find) in the future.
For the “think tank” …
Below is a 3D graphic of the field intensity for the conditions described there.
- The elevated, center-fed dipole is shown, with adjacent red lines displaying the current and phase distribution along the two sides of the dipole
- The feedpoint is shown by the red marker at the center of the dipole
- The loading coil is…
Unfortunately, the inexpensive receivers that show a signal strength value in “dBu” on their display screens are reporting only the conducted voltage that exists between the r-f input terminals of the receiver, not the field intensity value of the arriving radio wave — which is measured in units or sub-units of volts/meter.
The field…[Read more]
RE: … a rod antenna is not permitted for testing and that they must use a loop antenna…
My guess is that it relates to the relative susceptibility for the performance of these two antenna configurations to be affected by their construction and/or adjustment, and their nearby physical environment.
The checklist referred to, as well as that whole slide presentation was prepared by the FCC for the benefit of the contractors who are hired by manufacturers to perform FCC compliance tests and assemble the results into a format acceptable to the FCC — the goal being that of getting FCC authorization/certification for the sale of a product for…[Read more]
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