Mark wrote: Seems logical that if you want to protect something don’t have it connected to earth to make it easy for lightning to hit it, in this case the transmitter.
Connecting the chassis/r-f ground bus of the transmitter via a low-impedance path to the electrical potential of the Earth helps to protect the transmit system, because it “…[Read more]
ArtisanRadio wrote: The safest and most legal way to run a transmitter…is to install it at Earth level, using a short ground lead to one or more buried ground rods. …If you locate the transmitter well away from any obstructions, such as buildings, you’ll get as much range as an elevated install.
The first sentence in the clip above is a…[Read more]
Rich replied to the topic LITTLE KNOWN FCC EXCEPTION TO THE FM FIELD STRENGTH RULE in the forum Regulations / Law 2 months, 2 weeks ago
The title of FCC §15.231 seems appealing, but reading further into its following text brings disappointment (see below):
Below is a calculation of the performance of a “typical” Part 15 AM transmit system, from a spreadsheet using the appropriate equations appearing in antenna engineering textbooks.
The impedance of the antenna system “seen” by the transmitter there is the sum of the radiation resistance with the r-f resistances of the loading coil and the path to…[Read more]
Clearly Neil has taken the time to design, install, and optimize his transmit antenna system in order to achieve that 15-16 kHz audio frequency response at the output of his receiver.
Even if/when the transmitter itself has that modulating bandwidth, probably the r-f bandwidth of most Part 15 AM antenna systems, perfectly optimized, is narrower…[Read more]
Rich replied to the topic Does equipment need to be Part 15 Certified to operate legally? in the forum Regulations / Law 10 months, 4 weeks ago
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!”
Sorry, but the useful _day…[Read more]
Rich replied to the topic Please See Hobby Broadcaster Review of the Range Extender from ISS in the forum General Discussion 1 year, 2 months ago
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]
Rich replied to the topic Using Tecsun and Similar Receivers to "Measure" Field Intensity in the forum temp 1 year, 2 months ago
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]
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]
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