Source: https://part15.org/members/rich/buddyblog/
Timestamp: 2020-05-26 20:30:34
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Blog – Rich
IMO, the posts here on Part15.org lately are giving little reason for long-time members to stay here, or new readers to become members.
If this continues, the site will devolve into a small group of mutual admirers contributing little to those seeking accurate information about the installation and operation of Part 15 systems.
FCC §15.223 – AM Carrier Current Systems (1705 kHz to 10 MHz)
Below is a post I made in another thread here on Pt15us. However the subject of that thread would make it hard to locate for anyone searching for information on this topic. This re-post to my blog should be easier to find.
From §15.223: The field strength of any emission within the band 1.705-10.0 MHz shall not exceed 100 microvolts/meter at a distance of 30 meters. However, if the bandwidth of the emission is less than 10% of the center frequency, the field strength shall not exceed 15 microvolts/meter or (the bandwidth of the device in kHz) divided by (the center frequency of the device in MHz) microvolts/meter at a distance of 30 meters, whichever is the higher level. For the purposes of this section, bandwidth is determined at the points 6 dB down from the modulated carrier. The emission limits in this paragraph are based on measurement instrumentation employing an average detector. …
The text shown in bolded characters above permits the greatest field strength for a typical, legal AM transmit system permitted by this paragraph — which at a distance of 30 meters is 15 µV/m, not 100 µV/m.
Unfortunately, there are few, if any, consumer-level AM broadcast receivers (or receive locations, for that matter) where a signal strength of 15 µV/m would provide an acceptable/useful signal-to-noise ratio in the audio output of that receiver. Even if receivers could do that, a legal system under §15.223 could not provide a useful coverage area having a radius of a mile or more, unless all or most receivers in that area were located within a 30-meter distance from a radiating conductor of the a-c power lines.
AM broadcast receivers that are powered directly from the a-c line are close enough to it to receive a much higher, legal field strength than 15 µV/m, because they are in the extreme near field of the radiating conductor(s) of the a-c power line they are plugged in to. But that higher field drops very rapidly to below the noise floor when a battery-operated receiver such as a car radio or “Walkman” is located more than several meters away from the nearest radiating conductor of the a-c power lines.
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Post Audio Clip & Player on Part15us
I think I remember posts here including an audio player console loaded with an audio clip that plays with a single click.
Part 15 AM Coverage – High vs. Low Carrier Frequency
A NEC4.2 analysis shows this, for the system described:
2.8-meter, Base-fed, Base-loaded, Vertical Monopole
Monopole Base Elevation = 0.2 meters above the Earth
R-F Ground = 16 Buried Radials, 3 meters in length (each)
Radial Common Point Concentric with Vertical Axis of Monopole
Earth Conductivity = 5 mS/m, d.c. 13 (about average)
Applied R-F Power at Loading Coil Input = 80 mW, unmodulated
At 1650 kHz…
Loading Coil R-F Resistance at System Resonance = 20 Ω (assumed)
Groundwave Field Intensity at 1 mile = 84 µV/m
At 570 kHz…
Loading Coil R-F Resistance at System Resonance = 30 Ω (assumed)
Groundwave Field Intensity at 1 mile = 34 µV/m
(First posted to the forums in a thread topic that would make it hard to find again.)
The Basis for FCC NOUOs to Part 15 AM Operators
FCC §15.219(b) limits the total length of the antenna, feedline and ground lead to 3 meters.
A review of Part 15 AM NOUOs issued from FCC field inspections shows that if an installation does not meet §15.219(b), then they revert to §15.209 to judge its compliance.
If that inspected system is producing a field intensity at 30 meters greater than permitted by §15.209, THAT becomes the basis for an NOUO, rather than non-compliance with any part(s) of §15.219.
So ultimately, those NOUOs are based on excessive field strength.
Whether or not it was intended by the FCC, it is very easy to exceed the field strength at 30 meters permitted by §15.209 when using a 3-meter, base-loaded, Z-matched antenna system driven by many/most commercial Part 15 AM transmitters.
Part 15 AM users generally have been left to sort this out for themselves.
May 1, 2015 in Uncategorized
Someone on a hobby broadcaster website recently posted that the FCC does not keep track of old ham licenses.
Subsequently in that thread, he posted that he applied for a “vanity” ham callsign first used by someone that abandoned it about 50 years ago.
That FCC callsign (K8CBZ) first was issued in 1956 to yours truly, proof on request. I didn’t renew it because my interests evolved beyond ham radio toward commercial AM/FM/TV broadcast operations and engineering — a career path I followed until I retired in 1999.
Following the FCC application for vanity callsign K8CBZ reported by this poster on a hobby broadcast website, my original call letters were reassigned to him by the FCC, effective June 12, 2012.
This mystery has two parts:
1. If the FCC doesn’t keep track of old ham licences, how did it happen that this poster on a hobby broadcaster website was able to locate my original ham callsign?
2. But regardless, why did he choose to apply for it, no matter the method he used to find it?