AM BC Skywaves Measured With A Field Strength Meter

[Schroedingers Cat]

How many of you have measured AM BC skywaves with a field strength meter?

A couple of station engineers loaned me their old unused meters for a considerable length of time to keep the contacts cleaned from regular use, and I learned a lot about both actual groundwave (M-3 is just wrong for many places) and skywave field intensities. The most intense skywaves I have received were from WMVP, WOWO(before the night power reduction atrocity), and WCKY, which all maxed out around 10 mV/m in SE Michigan.

I know there are a lot of people here who have reported S meter results here, but unless you do an end to end dial comparison to the FI meter/rough calibration at various freqeuncies on your particular set, it is not that accurate. I know because I have tried. Even the older FI meters have considerable gain variations across the dial and have to be recalibrated for each frequency and use. Not sure if the new ones are better in that respect.

What kind of skywave field strengths have you seen?

Anyone know what are the actual field strengths of received North American stations DXed in northern Europe?

 

[K4WRF]

How many of you have measured AM BC skywaves with a field strength meter?

A couple of station engineers loaned me their old unused meters for a considerable length of time to keep the contacts cleaned from regular use, and I learned a lot about both actual groundwave (M-3 is just wrong for many places) and skywave field intensities. The most intense skywaves I have received were from WMVP, WOWO(before the night power reduction atrocity), and WCKY, which all maxed out around 10 mV/m in SE Michigan.

I know there are a lot of people here who have reported S meter results here, but unless you do an end to end dial comparison to the FI meter/rough calibration at various freqeuncies on your particular set, it is not that accurate. I know because I have tried. Even the older FI meters have considerable gain variations across the dial and have to be recalibrated for each frequency and use. Not sure if the new ones are better in that respect.

What kind of skywave field strengths have you seen?

Anyone know what are the actual field strengths of received North American stations DXed in northern Europe?

On another thread here, I was reminiscent of being able to receive skywave from WWL and WLAC with a crystal set back in the 50's. Each of these stations about 275 miles from my childhood home. Many years later I was there one night and recalled that instance, I had often wondered what the field strength must have been. I got the Potomac FIM-41 field meter out of my car and to my amazement measured as much as 35 mv/m on WWL and as much as 40 mv/m on WLAC. Each was experiencing considerable selective fades as expected. Way outside of what might be predicted in both cases.

 

[Schroedingers Cat]

Was it during quick fade ins characteristic of auroral and meteor trail reflection usually heard on high freqeuncies and above? I know that the skywave is supposed to be stronger the further south you go with the magnetic midpoint, but this exceeds what I also thought was possible. Being generous, say there was a 4000 mV/m inverse field at one mile. Inverse field would then be 40 mV/m at 100 miles if it were a nearly straight path. What's amplifying it? Was it near any tall vertical metal structures? I guess you could have a focusing effect if the ionic layer was properly shaped. I've heard of exceeding inverse field, but no one ever explained it to me. Using a semi calibarated S meter, I thought that WCFL was giving me 25 mV/m skywave at about 220 miles, but I never measured it that high with the FI meter, and the S meter was near where the breaker box was in the basement, and some other appliances that might have acted like an antenna inside a house.

 

[pianoplayer88key]

I've also recently wondered what the skywave field strengths of a few strong signals are.

For example, I'm about 300 miles west of 1580 KMIK at a heading of 262°, and they typically are my strongest nighttime skywave signal here. KMIK runs 50kW day and night, and their directional antenna at night puts a field of approximately 3,000 mV/m at 1 km toward me.

I've taken some photos of my Tecsun PL-606, coupled to a couple various antennas, showing signal strength on the display. (It's dBu referenced on the Si4734 DSP chip's input, not actual field strength.)

Barefoot PL-606 resting on top of my upright piano, showing 70dBu signal. There's also a PL-380 that's showing 62dBu, proof that the PL-380 is somewhat less sensitive, and the dBu isn't "God's Word" on actual field strength.
For comparison, several locals indicate as follows on the barefoot PL-606:
600 KOGO ~ 69dBu (5kW DA-1 @ 8 mi W)
690 XEWW ~ 70dBu day, 61dBu night (77kW/50kW DA-2 @ 32 mi SSW)
760 KFMB ~ 73dBu day, 82dBu night (5kW/50kW DA-N @ 7 mi NNW)
910 KECR ~ 69dBu day, 71dBu night (5kW DA-2 @ 9 mi N)
1130 KSDO ~ 74-76dBu (10kW DA-2 @ 6 mi N)
1170 KCBQ ~ 81dBu day, 68dBu night (50kW/2.9kW DA-2 @ 9 mi N - same site as KECR)
1360 KLSD ~ 70dBu day, 63dBu night (5kW/1kW ND @ 8 mi W - across highway from KOGO)
As you can see, several close strong signals are weaker than KMIK's peak, and only 4 or 5 stations exceed KMIK's peak signal.

PL-606 with Select-A-Tenna, showing 80dBu. I don't even think that's the peak signal, either, as when I peak my local 69dBu signal on KOGO the same way, the PL-606 indicates 86dBu.

PL-606 and Select-A-Tenna at a utility pole's ground wire, showing 91dBu. To get the same signal reading on the barefoot PL-606, I would probably have to be within 1/4 mile or less of the transmitter site. As with the SAT-aided photo, I also think that's not the peak, either - I get 96dBu (and slight overload) when peaking 1470 XERCN that way, a signal which only indicates ~63dBu on the stock PL-606's built-in ferrite. Peaking 910 KECR, as well as 760 KFMB's daytime signal, both result in the PL-606 pegging the meter at 98dBu and overloading.
In fact, KMIK's 2nd harmonic was showing a 22dBu signal with the same setup.

I understand R. Fry has a Tecsun PL-310, which has the same internal ferrite antenna and DSP chip as my PL-606, and I think he's done some field strength comparisons using that radio, but I can't find his post at the moment. I was wondering, would he have a way of approximating what field strength KMIK would likely be at my location? According to the FCC, I am 300 miles from them at a heading of 262°.
Also, speaking of field strength, at what point when getting close to a station do you stop taking ground conductivity (for groundwave) into account, and just use the inverse field? Also where do you stop taking into account the directional pattern, and calculate based on the non-directional field as specified in the FCC database entry? For example, if I was standing between two of 760 KFMB's 3 towers (a highway and an exit to a local cross street bisects 2 of the towers, and I've heard that 620 KTAR in Phoenix, AZ, straddles a Wal-Mart, among other sites that don't have the entire tower area land all to themselves), would I calculate the inverse non-directional field from KFMB's nearest tower to where I am, even though they are directional at night?

 

[Schroedingers Cat]

In reality, if you look at DA proofs, you start to get measurable ground conductivity losses within 0.1 km of the transmitter if the conductivity is pretty bad. I think R. Fry said that an added wire screen at the base of the towers can cut some losses, but once you're beyond the radials, it's pretty much independent of the construction, the ship has set sail.

http://www.its.bldrdoc.gov/pub/ntia-rpt/80-42/80-42_ocr.pdf

I wish that I had a 1960 NAB Handbook or old Part 73 Rules handy, but statistically extrapolating from FCC graphs the above link, I can't see the 99.7 percentile being more than about 0.7 mV/m at about 240 miles for a 100 mV/m @ 1 mile inverse field, and even that's well above inverse field. That's 9 dB above 10% skywave, or 2.67 standard deviations above the 50% skywave. 10% is 9 dB above 50%, and that's about 1.33 SD above the mean field strength. For a 2700 mV/m @ 1 mile inverse field, I can't see it really getting even to 15 mV/m, let alone 35 or 40 mV/m. I wonder if WWL and WLAC were doing superpower experiments.

 

[Schroedingers Cat]

All kinds of things can happen when you are really close to a transmitter. They usually recommend not taking directional fields before 5 to 10 times the distance between the closest towers of the array as I recall. Say you were equidistant between three towers that were 120 degrees out of phase and of equal intensity. Theoretically, there would be a place where the signal would be zero.

 

[radioman148]

I've also recently wondered what the skywave field strengths of a few strong signals are.

For example, I'm about 300 miles west of 1580 KMIK at a heading of 262°, and they typically are my strongest nighttime skywave signal here. KMIK runs 50kW day and night, and their directional antenna at night puts a field of approximately 3,000 mV/m at 1 km toward me.

I've taken some photos of my Tecsun PL-606, coupled to a couple various antennas, showing signal strength on the display. (It's dBu referenced on the Si4734 DSP chip's input, not actual field strength.)

Barefoot PL-606 resting on top of my upright piano, showing 70dBu signal. There's also a PL-380 that's showing 62dBu, proof that the PL-380 is somewhat less sensitive, and the dBu isn't "God's Word" on actual field strength.
For comparison, several locals indicate as follows on the barefoot PL-606:
600 KOGO ~ 69dBu (5kW DA-1 @ 8 mi W)
690 XEWW ~ 70dBu day, 61dBu night (77kW/50kW DA-2 @ 32 mi SSW)
760 KFMB ~ 73dBu day, 82dBu night (5kW/50kW DA-N @ 7 mi NNW)
910 KECR ~ 69dBu day, 71dBu night (5kW DA-2 @ 9 mi N)
1130 KSDO ~ 74-76dBu (10kW DA-2 @ 6 mi N)
1170 KCBQ ~ 81dBu day, 68dBu night (50kW/2.9kW DA-2 @ 9 mi N - same site as KECR)
1360 KLSD ~ 70dBu day, 63dBu night (5kW/1kW ND @ 8 mi W - across highway from KOGO)
As you can see, several close strong signals are weaker than KMIK's peak, and only 4 or 5 stations exceed KMIK's peak signal.

PL-606 with Select-A-Tenna, showing 80dBu. I don't even think that's the peak signal, either, as when I peak my local 69dBu signal on KOGO the same way, the PL-606 indicates 86dBu.

PL-606 and Select-A-Tenna at a utility pole's ground wire, showing 91dBu. To get the same signal reading on the barefoot PL-606, I would probably have to be within 1/4 mile or less of the transmitter site. As with the SAT-aided photo, I also think that's not the peak, either - I get 96dBu (and slight overload) when peaking 1470 XERCN that way, a signal which only indicates ~63dBu on the stock PL-606's built-in ferrite. Peaking 910 KECR, as well as 760 KFMB's daytime signal, both result in the PL-606 pegging the meter at 98dBu and overloading.
In fact, KMIK's 2nd harmonic was showing a 22dBu signal with the same setup.

I understand R. Fry has a Tecsun PL-310, which has the same internal ferrite antenna and DSP chip as my PL-606, and I think he's done some field strength comparisons using that radio, but I can't find his post at the moment. I was wondering, would he have a way of approximating what field strength KMIK would likely be at my location? According to the FCC, I am 300 miles from them at a heading of 262°.
Also, speaking of field strength, at what point when getting close to a station do you stop taking ground conductivity (for groundwave) into account, and just use the inverse field? Also where do you stop taking into account the directional pattern, and calculate based on the non-directional field as specified in the FCC database entry? For example, if I was standing between two of 760 KFMB's 3 towers (a highway and an exit to a local cross street bisects 2 of the towers, and I've heard that 620 KTAR in Phoenix, AZ, straddles a Wal-Mart, among other sites that don't have the entire tower area land all to themselves), would I calculate the inverse non-directional field from KFMB's nearest tower to where I am, even though they are directional at night?

Do you get KBLA mixing it up with KMIK at night?
When I was in Hawaii last year KBLA was an easy catch on 1580. I didn't hear KMIK.

 

[jd]

and I've heard that 620 KTAR in Phoenix, AZ, straddles a Wal-Mart

That's right, and KTAR was featured on Scott Fybush's "Tower Site of the Week": http://www.fybush.com/sites/2009/site-090918.html For the Google street (or parking lot) view, plug in 3713 East Thomas Road, Phoenix AZ.

 

[K4WRF]

Was it during quick fade ins characteristic of auroral and meteor trail reflection usually heard on high freqeuncies and above? I know that the skywave is supposed to be stronger the further south you go with the magnetic midpoint, but this exceeds what I also thought was possible. Being generous, say there was a 4000 mV/m inverse field at one mile. Inverse field would then be 40 mV/m at 100 miles if it were a nearly straight path. What's amplifying it? Was it near any tall vertical metal structures? I guess you could have a focusing effect if the ionic layer was properly shaped. I've heard of exceeding inverse field, but no one ever explained it to me. Using a semi calibarated S meter, I thought that WCFL was giving me 25 mV/m skywave at about 220 miles, but I never measured it that high with the FI meter, and the S meter was near where the breaker box was in the basement, and some other appliances that might have acted like an antenna inside a house.

No, measurements were made way out in the country. That instance was some years ago when I took that measurement (~25)but I do recall the selective fades were dramatic, frequent and very deep. Coincidentally, the location is on axis for the main lobe of both stations. I always thought that WWL experienced ground-wave/sky-wave cancellation at night as their Lake Ponchartrain transmitter location (at that time) did provide a marginal GW signal up there where it was out of the question for WLAC. WLAC always had issues with deep selective fades due to high-angle radiation at theta's of greater than 45 degrees. I never knew if this condition was because of the frequency, the different tower heights or a combination of all. Now I'm going to have to get that FIM out again!

 

[K4WRF]

All kinds of things can happen when you are really close to a transmitter.  They usually recommend not taking directional fields before 5 to 10 times the distance between the closest towers of the array as I recall.  Say you were equidistant between three towers that were 120 degrees out of phase and of equal intensity.  Theoretically, there would be a place where the signal would be zero.

This is true and more distance (though not required) should be used on arrays that are widely spaced. FIM orientation critical towards "array center", close in, the instrument is resolving the individual vectors off each tower rather than point source or sum of vectors.
w/

 

[gar hi]

I've also recently wondered what the skywave field strengths of a few strong signals are.

For example, I'm about 300 miles west of 1580 KMIK at a heading of 262°, and they typically are my strongest nighttime skywave signal here. KMIK runs 50kW day and night, and their directional antenna at night puts a field of approximately 3,000 mV/m at 1 km toward me.

Have you ever attempted to hear KMIK during the day or is it too high on the dial to put out a strong enough groundwave to make it that far?

There seems to be good conductivity between you and Tempe, Arizona.

 

[Schroedingers Cat]

I've also recently wondered what the skywave field strengths of a few strong signals are.

For example, I'm about 300 miles west of 1580 KMIK at a heading of 262°, and they typically are my strongest nighttime skywave signal here. KMIK runs 50kW day and night, and their directional antenna at night puts a field of approximately 3,000 mV/m at 1 km toward me.

I've taken some photos of my Tecsun PL-606, coupled to a couple various antennas, showing signal strength on the display. (It's dBu referenced on the Si4734 DSP chip's input, not actual field strength.)

Barefoot PL-606 resting on top of my upright piano, showing 70dBu signal. There's also a PL-380 that's showing 62dBu, proof that the PL-380 is somewhat less sensitive, and the dBu isn't "God's Word" on actual field strength.
For comparison, several locals indicate as follows on the barefoot PL-606:
600 KOGO ~ 69dBu (5kW DA-1 @ 8 mi W)
690 XEWW ~ 70dBu day, 61dBu night (77kW/50kW DA-2 @ 32 mi SSW)
760 KFMB ~ 73dBu day, 82dBu night (5kW/50kW DA-N @ 7 mi NNW)
910 KECR ~ 69dBu day, 71dBu night (5kW DA-2 @ 9 mi N)
1130 KSDO ~ 74-76dBu (10kW DA-2 @ 6 mi N)
1170 KCBQ ~ 81dBu day, 68dBu night (50kW/2.9kW DA-2 @ 9 mi N - same site as KECR)
1360 KLSD ~ 70dBu day, 63dBu night (5kW/1kW ND @ 8 mi W - across highway from KOGO)
As you can see, several close strong signals are weaker than KMIK's peak, and only 4 or 5 stations exceed KMIK's peak signal.

PL-606 with Select-A-Tenna, showing 80dBu. I don't even think that's the peak signal, either, as when I peak my local 69dBu signal on KOGO the same way, the PL-606 indicates 86dBu.

PL-606 and Select-A-Tenna at a utility pole's ground wire, showing 91dBu. To get the same signal reading on the barefoot PL-606, I would probably have to be within 1/4 mile or less of the transmitter site. As with the SAT-aided photo, I also think that's not the peak, either - I get 96dBu (and slight overload) when peaking 1470 XERCN that way, a signal which only indicates ~63dBu on the stock PL-606's built-in ferrite. Peaking 910 KECR, as well as 760 KFMB's daytime signal, both result in the PL-606 pegging the meter at 98dBu and overloading.
In fact, KMIK's 2nd harmonic was showing a 22dBu signal with the same setup.

I understand R. Fry has a Tecsun PL-310, which has the same internal ferrite antenna and DSP chip as my PL-606, and I think he's done some field strength comparisons using that radio, but I can't find his post at the moment. I was wondering, would he have a way of approximating what field strength KMIK would likely be at my location? According to the FCC, I am 300 miles from them at a heading of 262°.
Also, speaking of field strength, at what point when getting close to a station do you stop taking ground conductivity (for groundwave) into account, and just use the inverse field? Also where do you stop taking into account the directional pattern, and calculate based on the non-directional field as specified in the FCC database entry? For example, if I was standing between two of 760 KFMB's 3 towers (a highway and an exit to a local cross street bisects 2 of the towers, and I've heard that 620 KTAR in Phoenix, AZ, straddles a Wal-Mart, among other sites that don't have the entire tower area land all to themselves), would I calculate the inverse non-directional field from KFMB's nearest tower to where I am, even though they are directional at night?

tfcwings, see if you can get an old FI meter for a while. Make sure you follow all the instructions carefully, and plunk the Tecsun in the same spot, alternating with the FI meter, and do a bandscan, measuring each groundwave from one end of the dial to the other with each instrument, mV/m and dBu. If the ferrite rod is parallel to the long dimension of the Tecsun, put it perpendicular to the FI meter orientation on each measurement. That's what I would do, and just see what sense you can make of the readings on the Tecsun. Also, remember to recalibrate the FI meter for each frequency.

 

[pianoplayer88key]

Do you get KBLA mixing it up with KMIK at night?
When I was in Hawaii last year KBLA was an easy catch on 1580. I didn't hear KMIK.

Yes, KBLA can provide some stiff competition with KMIK, but it's usually when KMIK is fading. Almost always, KMIK's peaks are considerably stronger than those of KBLA, usually rendering Santa Monica practically unreadable. When KMIK is fading, though, the audio phase distortion and KBLA being something like 7-10 Hz (estimated) off frequency can be very annoying.

Have you ever attempted to hear KMIK during the day or is it too high on the dial to put out a strong enough groundwave to make it that far?

There seems to be good conductivity between you and Tempe, Arizona.

Around midday in summer, KBLA owns the frequency, but it's barely above the noise without a tuned loop, and some radios don't hear it then at all. In fact, I have yet to confirm any possible trace of 550 KFYI here midday, either (having a local on 540 doesn't help, either), and 620 KTAR, besides being covered by local XESS, wasn't receivable when XESS wasn't on 620. (Back then, though, I only had a radio with poor selectivity, so 600 KOGO spilled over onto 620, killing anything that may have been lurking beneath.)
In winter, though, I do sometimes hear KMIK midday, especially with the loop, and it sometimes even overpowers KBLA. In January, a couple times I thought I heard 1550 KUAZ Tuscon, AZ, mixing it up with co-channel semi-local XEBG Tijuana.

 

[pianoplayer88key]

tfcwings, see if you can get an old FI meter for a while. Make sure you follow all the instructions carefully, and plunk the Tecsun in the same spot, alternating with the FI meter, and do a bandscan, measuring each groundwave from one end of the dial to the other with each instrument, mV/m and dBu. If the ferrite rod is parallel to the long dimension of the Tecsun, put it perpendicular to the FI meter orientation on each measurement. That's what I would do, and just see what sense you can make of the readings on the Tecsun. Also, remember to recalibrate the FI meter for each frequency.

My dad has, I think, a Stoddart NM-20. Would that work?

 

[Schroedingers Cat]

Does it have a self contained standard loop antenna for AM BC? Has it been calibrated recently?

Since you seem inclined to do this, and it would be a valuable exercise, you might as well do it as accurately as possible. If you know any of the chief engineers at the local stations that are directional, you might ask them if they have one to spare Potomac or RCA to loan for such a project. Tell them what you want to do, and I think they would help you out.

I would think that what you will find in this case is that you mainly need a dB "fudge factor" at each frequency to add or subtract to make the dBu reading at each frequency equal the actual measured field strength converted to dBu, and hence back to field strength. This will compensate for the inevitable gain and antenna efficiency differences across the nearly 3 1/2 to 1 frequency range. You could measure as many stable groundwaves possible, and draw a graph of the dB "fudge factor" vs. frequency. You can then interpolate between the measured frequencies to obtain the 'fudge factors" for in between frequencies.

Say for example you have a 3.16 mV/m measured FI field strength. Converting this to dBu, it is 70 dBu. Say your reading on the Tecsun is 62, then your fudge factor is +8 at that frequency. If your reading is 75, then your fudge factor is -5 for that frequency.

All of this assumes that the meter is fairly log linear. Do tech specs say that it is a dBu scale on the Tecsun? Then that should be fairly accurate, as 1 dB represents about a 10% change in FIELD STRENGTH. So the best accuracy possible is about 10%. Not good enough for proofs and applications, but it will answer a lot of questions.

 

[pianoplayer88key]

Does it have a self contained standard loop antenna for AM BC? Has it been calibrated recently?

I don't remember what it has - it may even be a whip. Haven't used it in several years.

Since you seem inclined to do this, and it would be a valuable exercise, you might as well do it as accurately as possible. If you know any of the chief engineers at the local stations that are directional, you might ask them if they have one to spare Potomac or RCA to loan for such a project. Tell them what you want to do, and I think they would help you out.

Unfortunately I don't know any of them personally.

I would think that what you will find in this case is that you mainly need a dB "fudge factor" at each frequency to add or subtract to make the dBu reading at each frequency equal the actual measured field strength converted to dBu, and hence back to field strength. This will compensate for the inevitable gain and antenna efficiency differences across the nearly 3 1/2 to 1 frequency range. You could measure as many stable groundwaves possible, and draw a graph of the dB "fudge factor" vs. frequency. You can then interpolate between the measured frequencies to obtain the 'fudge factors" for in between frequencies.

Say for example you have a 3.16 mV/m measured FI field strength. Converting this to dBu, it is 70 dBu. Say your reading on the Tecsun is 62, then your fudge factor is +8 at that frequency. If your reading is 75, then your fudge factor is -5 for that frequency.

All of this assumes that the meter is fairly log linear. Do tech specs say that it is a dBu scale on the Tecsun? Then that should be fairly accurate, as 1 dB represents about a 10% change in FIELD STRENGTH. So the best accuracy possible is about 10%. Not good enough for proofs and applications, but it will answer a lot of questions.

The Tecsun PL-606 I use does use a dBu scale, with the capability of reading from 15 dBu to 98 dBu. Scott Willingham, who works for SiLabs (the company that designed the chip), said, IIRC, that it's referenced to input voltage on the chip.
It will often have varying noise floors, depending on the strength of local signals elsewhere on the dial. For example, if I'm maybe within 1/2 mile or so of a powerful station's transmitter, it will often show 49 or 50dBu across a couple kHz of spectrum, and have no audible signal. In a somewhat rural place, I might see a reading of 15dBu and a SNR of maybe 18dB or so. At home, if I set up the shortwave antenna properly, it's possible to get a 15dBu signal reading with 25dB SNR (max it will display there) on 2340kHz, the 2nd harmonic of 1170.
That station, KCBQ, 9.3 miles from me, typically indicates about 81dBu on its fundamental in the daytime. I've noticed that once the display rises over about 80dBu or so, it seems to flatten out, and doesn't hit 90dBu until I'm within about 1/4 mile of the 50kW transmitter. Also, when I peak a weaker signal with the Select-A-Tenna, it may take a 35dBu signal up to like 55dBu or so, but that 81dBu signal will only go up to maybe 88 or 89dBu. Sometimes it will briefly show 90dBu, then snap back down to 87dBu or so.
There's also a signal on 760 that's 50kW nights from 7.3 miles away, and it indicates 82dBu on its fundamental. If I put the PL-606 over the copper water pipe under the floor in the bathroom, it'll show 88dBu. There, using the Select-A-Tenna may briefly make it show 93dBu, then a second later it snaps down to 87dBu. Using it at a utility pole, like was pictured with my 91dBu reading on 1580, will take it to 98dBu both on 1170 in the daytime and 760 at night. Above about 95 or 96dBu, it audibly overloads / distorts on the fundamental frequency.

Also I suspect that a 3.16mV/m FS is going to register quite a bit lower than 70dBu. I'm located near 32°45'40"N 116°56'50"W, and below are the distances, headings from me to their transmitter (and back), power, specified field @ 1 km for DA or antenna height for ND, and PL-606 readings for a few local signals. According to the M3 map, I live in an area where the ground conductivity is "8", and a few miles west of me, parallel to the coast, it says "15". (Of course I realize it's not gospel.) Field will be the highest one used for that station (Theoretical, Standard, Augmented). All are daytime readings, except for a few specified night ones.
600 KOGO - 7.62 mi - 248.77° (68.71°) - 5 kW DA - A=5,01.99 mV/m @ 1 km - 68 dBu
690 XEWW - 32.37 mi - 188.59° (8.54°) - 77 kW DA - S=4,127.80 mV/m @ 1 km - 70 dBu - this is still listed as XETRA\
760 KFMB - 7.21 mi - 321.25° (141.21°) - 5 kW ND - 87.60° - 72 dBu
^^^^ night - 50 kW DA - A=1,995.00 mV/m @ 1 km - 82 dBu
910 KECR - 9.34 mi - 7.84° (187.85°) - 5 kW DA - S=749.41 mV/m @ 1 km - 69 dBu
^^^^ night - 5 kW DA - S=1,024.68 mV/m @ 1 km - 71 dBu
1040 KURS - 11.13 mi - 245.49° (65.40°) - 0.37 kW ND - 169.30° - 51 dBu
^^^^ night - supposed to drop down to 0.061 kW ND, but I think they've been staying on day power, but they do have fading at night.
1130 KSDO - 6.29 mi - 351.01° (171.00°) - 10 kW DA - S=1,070.11 mV/m @ 1 km - 77 dBu
1170 KCBQ - 9.34 mi - 7.84° (187.85°) - 50 kW DA - S=4,132.53 mV/m @ 1 km - 81 dBu
^^^^ night - 2.9 kW DA - S=1,025.95 mV/m @ 1 km - 69 dBu
1240 KNSN - 11.13 mi - 245.49° (65.40°) - 0.55 kW ND - 201.90° - 61 dBu
1360 KLSD - 8.21 mi - 254.99° (74.92°) - 5 kW ND - 184.50° - 70 dBu
^^^^ night - 1 kW ND - 65 dBu
1470 XERCN - 18.06 mi - 182.57° (2.56°) - 10 kW ND - 141.20° - 63 dBu - FCC says it's 5 kW but I think I've heard them ID in spanish as being 10 kW

At my grandma's house, 23kW/1kW DA-2 1300 KAZN and 50kW/9.8kW 1430 KMRB are 1/3 mile NNW, heading about 315°. When I had the Grundig G8 there (I no longer have it), I was getting readings anywhere from 83 to 88 dBu or so. I haven't taken the PL-606 there yet, and the PL-380 pegs at 63 dBu. Also, 1110 KDIS, about 4.6 miles to the east, reads in the low to mid 80s dBu on the G8 (can't remember the exact reading) in the daytime.

I should maybe see if my dad's Stoddart still works. Maybe that might be adequate for experimentation? (I think it's probably 1940s or 1950s vintage, and he was telling me he remembers it having problems with drift, especially if it's not warmed up enough.)



Also, does anyone know why I keep getting a "session timed out" error when trying to post in my normal browser? I even tried logging out, like it said, and got session verification failed, please try logging out and back in again. Switching to another browser, on which I hadn't been logged in, allowed me to post.

 

[Schroedingers Cat]

You might also try calling the electrical engineering department of a nearby university. I know O.G. Villard, Jr., a fascinating EE, antenna expert, and DXer, was out there somewhere, but he passed away. If you find a person with similar interests, they may want to help you with the project, perhaps even do a research project. W9WI and Scott Fybush may also have some suggestions of a radio contact that could help you.

I used to think M-3 was accurate also, and tried to make sense of S meter and signal strength meter readings with those, but I found that they are inaccurate also. In Michigan, there are many areas that say 8 on the M-3 Map, and measured radials and proofs show 0.1 to 3.

You might find a real klunker FI meter online, but it would probably need recalibration and repair, which would make the cost a lot more.

I used to have a lot of radio engineer contacts, but many have passed away, and others sold their meters when they no longer needed them.

 

[Schroedingers Cat]

What is the FM signal indicator like?

Have you noticed any effect the piano strings have on either AM or FM reception?

 

[Schroedingers Cat]

Another thing to look out for, pianoplayer, is if the Tecsun seems to max out at a certain dB level. The Technics ST-G5 series had a maximum reading of 54-58 dB. If the meter is non log linear at the ends of the range, you need to have an attenuator to extend the range and put the signal range in a log linear portion.

I have not yet seen enough data, even with R. Fry's study, to make a decision as to whether this could be semi calibrated. You need to do a fudge factor vs. frequency study with identical location FI meter readings. And you need to see if there is any nonlinearity in the scale. DA-1 (U3) stations and nondirectional stations (U1) with different power levels are good to study linearity. Check for maxing out or low end squeezing together of predicted signals that should vary considerably but read nearly the same. Look at the theoretical inverse fields online to see if they make sense, or if there is a grandfathered reduced input power.

Realize also that signals vary considerably both diurnally and from one day and particularly seasonal measurement to the next. Do them during noncritical hours. Do them the same day preferably. The inaccuracy of various locations and times is eliminated by side by side measuring on the same day. Remember to recalibrate the FI meter for each reading.

 

[crainbebo]

At my house, KIXI 880 in the daytime is rated around a 85/25 on the Grundig G8, 85 dBu and 25 db. It drops slightly at night, where it is around 81/25 or so.

KKNW 1150 is around 84/25, and KXPA 1540 is about an 80/25 at the highest.

-crainbebo