Hi all... I'm trying to figure out a few things...
For one thing, I'm trying to figure out how far a signal, given a specific power, antenna (assuming non-directional operation), and constant ground conductivity along the path, would go. I'm using the FCC Figure 8 calculator and groundwave curves, but am having difficulty figuring some things out.
For one example, I would like to find how far a 2.5 megawatt (I'm aware of stations in other countries that have operated with that power level) signal on 540 kHz into a Franklin antenna (like KFBK or KSTP) would go over saltwater until it's barely intelligible on a few various radios.
The FCC calculator won't let me calculate the field for a Franklin antenna, unfortunately. I have kind-of found a workaround by finding specs that result in 1/2 that of KSTP's non-directional daytime Franklin antenna (179.4+179.4°), but don't know how to figure out the field for a KFBK 180+180° antenna. Also, the calculator won't display fields over 9999mV/m @ 1 km, but by quartering the power (which halves the field strength) then adjusting accordingly I'm able to figure out that 2.5 MW into a KSTP franklin would be about 25,588.48 mV/m @ 1 km. (KSTP itself is specified in the FCC as having an efficiency of 511.77 mV/m @ 1 km for 1 kW.) However, as KSTP isn't a full 180+180° antenna like KFBK, I'm thinking my calculations haven't attained the ideal spec. Any suggestions on how to calculate it?
Also I've downloaded the FCC database files, but am having difficulty figuring out how to put the various things together. For example, I was wanting to find out what stations use 180.00° towers. I found the tower data in am_towers.dat, but as there's no facility_id column in that pipe-delimited file, I can't seem to match those with the appropriate stations. Any ideas on how to do this? (I have OpenOffice, and was experimenting with importing a couple database files into its calc program.)
As for figuring out the range of the above signal, that's proving to not be easy, as well. In reading various posts, apparently Radio-Locator's "fringe" 150µV/m signal is considered unusable by most people, but a pest by DXers. Another post refers to 560 WIND Chicago being heard with a very weak 25µV/m groundwave signal somewhere, and 1400 WOND was heard at Bermuda at 7µV/m, very weak but enough above the noise to be detectable on a very good receiver. Also calculating from my Tecsun PL-606's specified 1 mV/m @ 26dB SNR sensitivity results in a theoretical noise floor of about 50µV/m or so. (I don't think this is entirely accurate, though, as my PL-380 has the same spec, but a different antenna and seems to be a few dB less sensitive than the PL-606, which according to someone on a yahoo ultralightdx group uses the same antenna as the PL-310.)
I can't seem to calculate the distance to the 7µV/m contour of the above mega signal, though. That would require me to read the graph at a level of 0.000027356mV/m (taking into account the conversion factor, as the graph assumes 100mV/m @ 1 km), and it only goes down to 0.0001 mV/m. I was able to calculate a distance of 1305 miles (2100 km) at 25µV/m over saltwater, though, as it was right at the bottom of the scale. However, this is still not as far as the 2158 mi / 3474 km distance at which someone using a Sony ICF-6500W was "clearly able to copy" 560 WQAM Miami, FL, while at Signal Hill, Newfoundland. Considering that, I'm thinking a 2.5 megawatt signal into a Franklin that's heard with an excellent radio and antenna should go quite a bit farther than that over saltwater until it's unintelligible, but.... how far?
Also, I don't know at what signal level various radios, assuming there's no interference from any man-made sources and any naturally-occuring atmospheric noise, etc, is at its lowest level, would lose reception of a signal, or at least have it severely degraded. I'll post a few short sound clips of a few signals here. Most of them were actually recorded off locals, I just used a portable radio that I know has terrible sensitivity (for example a 1 mV/m signal is near the noise floor on this radio), rotated to null the signal some, and a detuned external loop antenna to further null the signal.
Barely detectable signal - I can recognize a song that's playing near the beginning of the clip, and can tell there's audio there, but can't make out what it's saying. (The only reason I know that it's in Spanish is because I know that station, 910 KECR, broadcasts that language at that time of day.)
Faint but intelligible signal. The music at the beginning of this clip is easier for my ear to hear, and if I pay careful attention while using sound-isolating earphones in a quiet environment I can make out what the announcer is saying in Spanish.
Somewhat weak, but easily intelligible signal. I would readily listen to a signal at this level, and maybe even a bit weaker, without having to think twice. I could even settle for the above example (#2) if I had to, but would prefer something more like this.
And, for a couple stronger ones...
Fair signal - this one barely lit the "tune" indicator on that radio. AFAIK some radios that have a "scan" or "seek" function would trip at a similar level.
Strong signal. This one actually does have a little bit of noise detectable in it, but that's due either to problems in the recording process, or the radio's internal noise floor. I could reduce the signal strength on the radio by about 30 dB, and still have the same SNR. BTW that's what I consider a "clear" or "full quieting" signal - a signal above which your radio's SNR is saturated. (It's 760 KFMB, and was indicating about 90/25 on the PL-606, aided by the Select-A-Tenna.)
BTW, using the 1-9 S-meter scale, I would rank the above 5 clips as follows: the first 2 would be S1, the 3rd would be S3 (when I recorded it I was thinking it was S2, but in listening a few minutes ago realized it was really more like S3), the 4th would be about S4 or maybe S5, and the last would be S9. (An S7 signal would also be full quieting / saturating the receiver SNR as well, and higher signal levels would be calculated based on how wide the signal splattered or how wide the front-end was desensed.) BTW... would it be possible, either with a properly designed digital transmission system, or DSP in the receiver, to decode the weakest example signal (meaning that's what it would sound like if it was an analog signal using a non-DSP receiver) and have it sound as good as the strong one? Also, when David Eduardo mentions that a major metro area like Los Angeles needs a 10 mV/m signal to be heard, does that mean the noise level is so high that you need 10 mV/m just to get up to the level of signal in the 1st or 2nd clip?
Now... at what approximate field strengths under ideal conditions would produce the lower 3 signal levels on a few radios? Examples include:
Tecsun PL-310 - I understand R Fry has one, and it has the same antenna as my PL-606
Si4734-equipped radio with a 3"x0.375" Amidon Type-61 ferrite bar wound with 40/44 Litz wire at the proper inductance for optimum MW reception (or maybe a 7.5"x0.5" bar, a 4"x0.25" bar or a 2"x0.25" bar)
Sony SRF-59 (I have one, not sure who else here does - seems to be quite sensitive for its size)
Perseus SDR with a beverage antenna or a very large (several (dozen?) feet diameter) tuned loop antenna
You could substitute other radios, but I'm especially interested in the first example or two, and a top-end radio with an excellent antenna, and maybe one or two in between and possibly a crystal set (to go to the opposite extreme from the ideal receiver).
(P.S. would this post have been more at home in the Engineering board?)
For one thing, I'm trying to figure out how far a signal, given a specific power, antenna (assuming non-directional operation), and constant ground conductivity along the path, would go. I'm using the FCC Figure 8 calculator and groundwave curves, but am having difficulty figuring some things out.
For one example, I would like to find how far a 2.5 megawatt (I'm aware of stations in other countries that have operated with that power level) signal on 540 kHz into a Franklin antenna (like KFBK or KSTP) would go over saltwater until it's barely intelligible on a few various radios.
The FCC calculator won't let me calculate the field for a Franklin antenna, unfortunately. I have kind-of found a workaround by finding specs that result in 1/2 that of KSTP's non-directional daytime Franklin antenna (179.4+179.4°), but don't know how to figure out the field for a KFBK 180+180° antenna. Also, the calculator won't display fields over 9999mV/m @ 1 km, but by quartering the power (which halves the field strength) then adjusting accordingly I'm able to figure out that 2.5 MW into a KSTP franklin would be about 25,588.48 mV/m @ 1 km. (KSTP itself is specified in the FCC as having an efficiency of 511.77 mV/m @ 1 km for 1 kW.) However, as KSTP isn't a full 180+180° antenna like KFBK, I'm thinking my calculations haven't attained the ideal spec. Any suggestions on how to calculate it?
Also I've downloaded the FCC database files, but am having difficulty figuring out how to put the various things together. For example, I was wanting to find out what stations use 180.00° towers. I found the tower data in am_towers.dat, but as there's no facility_id column in that pipe-delimited file, I can't seem to match those with the appropriate stations. Any ideas on how to do this? (I have OpenOffice, and was experimenting with importing a couple database files into its calc program.)
As for figuring out the range of the above signal, that's proving to not be easy, as well. In reading various posts, apparently Radio-Locator's "fringe" 150µV/m signal is considered unusable by most people, but a pest by DXers. Another post refers to 560 WIND Chicago being heard with a very weak 25µV/m groundwave signal somewhere, and 1400 WOND was heard at Bermuda at 7µV/m, very weak but enough above the noise to be detectable on a very good receiver. Also calculating from my Tecsun PL-606's specified 1 mV/m @ 26dB SNR sensitivity results in a theoretical noise floor of about 50µV/m or so. (I don't think this is entirely accurate, though, as my PL-380 has the same spec, but a different antenna and seems to be a few dB less sensitive than the PL-606, which according to someone on a yahoo ultralightdx group uses the same antenna as the PL-310.)
I can't seem to calculate the distance to the 7µV/m contour of the above mega signal, though. That would require me to read the graph at a level of 0.000027356mV/m (taking into account the conversion factor, as the graph assumes 100mV/m @ 1 km), and it only goes down to 0.0001 mV/m. I was able to calculate a distance of 1305 miles (2100 km) at 25µV/m over saltwater, though, as it was right at the bottom of the scale. However, this is still not as far as the 2158 mi / 3474 km distance at which someone using a Sony ICF-6500W was "clearly able to copy" 560 WQAM Miami, FL, while at Signal Hill, Newfoundland. Considering that, I'm thinking a 2.5 megawatt signal into a Franklin that's heard with an excellent radio and antenna should go quite a bit farther than that over saltwater until it's unintelligible, but.... how far?
Also, I don't know at what signal level various radios, assuming there's no interference from any man-made sources and any naturally-occuring atmospheric noise, etc, is at its lowest level, would lose reception of a signal, or at least have it severely degraded. I'll post a few short sound clips of a few signals here. Most of them were actually recorded off locals, I just used a portable radio that I know has terrible sensitivity (for example a 1 mV/m signal is near the noise floor on this radio), rotated to null the signal some, and a detuned external loop antenna to further null the signal.
Barely detectable signal - I can recognize a song that's playing near the beginning of the clip, and can tell there's audio there, but can't make out what it's saying. (The only reason I know that it's in Spanish is because I know that station, 910 KECR, broadcasts that language at that time of day.)
Faint but intelligible signal. The music at the beginning of this clip is easier for my ear to hear, and if I pay careful attention while using sound-isolating earphones in a quiet environment I can make out what the announcer is saying in Spanish.
Somewhat weak, but easily intelligible signal. I would readily listen to a signal at this level, and maybe even a bit weaker, without having to think twice. I could even settle for the above example (#2) if I had to, but would prefer something more like this.
And, for a couple stronger ones...
Fair signal - this one barely lit the "tune" indicator on that radio. AFAIK some radios that have a "scan" or "seek" function would trip at a similar level.
Strong signal. This one actually does have a little bit of noise detectable in it, but that's due either to problems in the recording process, or the radio's internal noise floor. I could reduce the signal strength on the radio by about 30 dB, and still have the same SNR. BTW that's what I consider a "clear" or "full quieting" signal - a signal above which your radio's SNR is saturated. (It's 760 KFMB, and was indicating about 90/25 on the PL-606, aided by the Select-A-Tenna.)
BTW, using the 1-9 S-meter scale, I would rank the above 5 clips as follows: the first 2 would be S1, the 3rd would be S3 (when I recorded it I was thinking it was S2, but in listening a few minutes ago realized it was really more like S3), the 4th would be about S4 or maybe S5, and the last would be S9. (An S7 signal would also be full quieting / saturating the receiver SNR as well, and higher signal levels would be calculated based on how wide the signal splattered or how wide the front-end was desensed.) BTW... would it be possible, either with a properly designed digital transmission system, or DSP in the receiver, to decode the weakest example signal (meaning that's what it would sound like if it was an analog signal using a non-DSP receiver) and have it sound as good as the strong one? Also, when David Eduardo mentions that a major metro area like Los Angeles needs a 10 mV/m signal to be heard, does that mean the noise level is so high that you need 10 mV/m just to get up to the level of signal in the 1st or 2nd clip?
Now... at what approximate field strengths under ideal conditions would produce the lower 3 signal levels on a few radios? Examples include:
Tecsun PL-310 - I understand R Fry has one, and it has the same antenna as my PL-606
Si4734-equipped radio with a 3"x0.375" Amidon Type-61 ferrite bar wound with 40/44 Litz wire at the proper inductance for optimum MW reception (or maybe a 7.5"x0.5" bar, a 4"x0.25" bar or a 2"x0.25" bar)
Sony SRF-59 (I have one, not sure who else here does - seems to be quite sensitive for its size)
Perseus SDR with a beverage antenna or a very large (several (dozen?) feet diameter) tuned loop antenna
You could substitute other radios, but I'm especially interested in the first example or two, and a top-end radio with an excellent antenna, and maybe one or two in between and possibly a crystal set (to go to the opposite extreme from the ideal receiver).
(P.S. would this post have been more at home in the Engineering board?)
