Following up on yesterday's power reading... 22 25 at the campus boundary, which is a public sidewalk... we wondered how much farther out we'd find the target minimum field reading of about 08 08, and we walked out 30-feet to the streetsign island that divides two confluencing streets, where the reading was 06 09, which equates with a reducewd signal submerged in FM fizz-noise.
Therefore 08 08 would be found in the main lane of the street and there's no audience there so the signal loses its meaning by being there.
With a "useful" signal range of 125-feet we are safely under the FCC's published allowance of 200-feet, so we'll stop here and make no more adjustments.
Besides using the TECSUN radio for our own compliance with FCC part 15, we have shown that these dBu/SN type radios CAN be used to setup for compliance.
We therefore now REQUIRE that all part 15 stations obtain and keep a radio with dBu and SM readouts. Deadline for compliance is 12 noon Decewmber 25th.
It may appear to some that many/most of the FCC §15.239 NOUOs are issued to operators of unlicensed systems using "high power" transmitters running tens or hundreds of watts, and that otherwise, there isn't much need be concerned.
But there are cases where NOUOs have been issued for systems radiating far less power (see graphic below).
Note that the radiated powers in the table apply only to free space fields. Signal reflections from the earth and other objects can either reinforce, or reduce them at some locations in the propagation environment.
Hobby Agent says: "There are cases where NOUOs have been issued for systems radiating far less power (see graphic). Signal reflections from the earth and other objects can either reinforce, or reduce them at some locations in the propagation environment."
While it is true that small numbers can be broken down into many many many smaller numbers into infinity, it is not clear whether this is a warning that an NOUO will be sent to KDX for being recievable to a drop-off distance of 125'.
It is not obvious whether the graphic table relates to the TECSUN line of radios with their dBu/SN indicators.
Possibly the posting does not address this thread in any particular way and should be given its own thread.
How did the FCC make measurements at a distance of 3 meters from the source? Were they trespassing? What if the antenna is on a 20 foot pole? Did they use a high reach? Something looks suspect here.
From Reply 18 above: ... It is not obvious whether the graphic table relates to the TECSUN line of radios with their dBu/SN indicators. ...
No, it does not.
The Tecsun PL-310 and similar receivers do not measure/display the net field intensity of the e-m wave(s) arriving at the antennas of those receivers.
"Most S meters on traditional analog receivers are not calibrated and in practice can only provide a relative measure of signal strength based on the receiver's AGC voltage. Some S meters on traditional analog receivers are calibrated to read S9 for an input of -73 dBm but do not provide the correct 6 dB per S unit correspondence.
Often the correlation between a radio listener's qualitative impression of signal strength and the actual strength of the received signal on an analog receiver is poor, because the receiver's AGC holds the audio output fairly constant despite changes in input signal strength."
DHR branches onto a path not previously taken in this thread about the field number readings on TECSUN-type radios.
Heretofore there has been no mention of "S" meters, but it's not unreasonable to take them under consideration as being less accurate signal-level indicators, in that they produce no numbers, other than the inaccurate number associated with "S9", as indicated.
However, to make use of both signal reading methods, that is by combining dBu indicators with "S" meters, a low power radio station expands its view of the RF field within the few feet being observed.
RE: ... this thread about the field number readings on TECSUN-type radios. ...
Once again, Tecsun PL-310 and similar radios do NOT display "field number readings."
The numbers Carl and others see is a function of voltage across the antenna terminals. In most cases as with a portable radio the impedance may be unknown.
Also to further rebuff Carl's comment: S9 is generally accepted to 50 uV across 50 ohms.
DHR used the expression: "To further rebuff Carl's comment..."
The practice of rebuffing can really bring out a shine in marble floor tiles.
But I have not been rebuked!
And no matter what gets said, the readings I took WERE taken outdoors IN A FIELD!
Carl's home is large enough to have a field inside. I am guessing that the grass grows slowly.
Grass roots radio.
RE: ... S9 is generally accepted to (be) 50 uV across 50 ohms.
However that does not mean that the net field intensity arriving at the receive antenna equals 50 µV/m.
The reason for that (Carl), mostly is due to the unknown/uncalibrated characteristics of the receive antenna system at the received frequency.
A web-sourced definition of field intensity is "... electric fields created by electric charges, and by time-varying magnetic fields. The units of the electric field in the SI system are newtons per coulomb (N/C), or volts per meter (V/m)."
The electric fields of interest here exist between two different physical points in space -- not a conducted voltage existing between two terminals inside a radio receiver.
The FCC uses units of field intensity in several of its Part 15 rules applying to unlicensed use of the AM & FM broadcast bands. Examples are §15.209 for the AM band and §15.239 for the FM band.
Measuring such electric fields _accurately_ requires calibrated (expensive) test equipment used correctly by a skilled and experienced operator.
As has been said: "The FCC uses units of field intensity in several of its Part 15 rules applying to unlicensed use of the AM & FM broadcast bands. Examples are §15.209 for the AM band and §15.239 for the FM band. Measuring such electric fields _accurately_ requires calibrated (expensive) test equipment used by a skilled and experienced operator."
And again, while it is good for the hobbyist to realize this in principle, the "calibrated expensive test equipment" that he will never own must be done without, leaving miniature radio stations with whatever make do solutions they can concoct.
RE: ...leaving miniature radio stations with whatever make do solutions they can concoct.
Preferably also with an understanding that such an approach is very unikely to provide the hoped-for "proof" or assurance desired for it.