Schroedingers Cat said:
My experience in the last few years is that there may be skywave of some intensity, perhaps very low, much of the time. At AM Broadcast frequencies, you can tell by a cyclic variation in the field strength of the assumed groundwave. If the skywave is 10% of the groundwave, the field strength will vary from 90% to 110% of the mean value as the phase of the skywave compared to the groundwave changes.
Ahh... one reason I asked is because I'm wanting to do some experimenting, including comparing sensitivity of a few radios, gain of a few antennas, etc, and I think it'd be easier if the signal strength was constant (or at least within a 0.5dB range) for the experiments. I do, too, hope to check frequencies at the top of the band, where skywave would be most likely.
About that variation, though, how do you tell whether you have groundwave or skywave when the signal strength indicator isn't moving off mminimum, the signal is barely audible, or there's fading due to there also being two other carriers present whose signals are maybe 0.033 Hz and 0.0056 Hz off frequency of the target?
gar fla said:
My brother lives in Hawaii near Hilo and a while back, I asked him if he could hear KSFO, KFI, or KNBR at the beach there during the day.
He got the chance to go to one of the beaches on the south side of the big island. He listened and said he couldn't hear anything.
He was using a Grundig G5 but no loop was involved. I don't know how big the internal ferrite antenna of that radio is but I wonder if using a radio like my Sangean PR-D5 (which has a 200 mm ferrite antenna) and the Terk AM Loop that I also use would have made a difference.
Also I wonder if being on the northeast side would have made any difference?
radioman148 said:
Getting MW groundwave signals from the west coast to Hawaii would seem almost impossible to me. I would have to see absolute indisputable evidence to be convinced that this could happen.
Interesting. I was able to get an easily listenable (better than armchair copy?) signal in Ocean Beach, CA, from lowly 500-watt high-dial 1290 KZSB Santa Barbara, CA, just over 180 miles distant, using only an ultralight - a Tecsun PL-606 with its internal 100mm ferrite. For proof,
here's a recording. Except for less than a half mile at each end, the path is entirely saltwater. (The fading was due to adjusting the radio during the recording.) The SNR indicator on the radio was pegged at 25dB.
If 500 watts that high up the dial can make it that far with that strong of a signal on a small radio, then what about a signal on 640 (KFI) or 680 (KNBR) (less groundwave loss due to frequency), running 50kW (20dB stronger) with KFI or KNBR's more efficient antennas, received with a high-end communications receiver and multi-wavelength beverage antenna (which I would expect to be at least 120dB, maybe 180dB more sensitive than the ultralight with its built-in ferrite)?
Schroedingers Cat said:
From Graph 1, 540-560 kHz. 1040 miles=1674 kilometers. From FCC database, WQAM daytime inverse field is 664.1 mV/m @ 1 km. At 1674 km, the reference field for 100 mV/m inverse field over 5000 mS/m is .00055 mV/m. Predicted field would be .003653 mV/m or 3.653 uV/m. Without a longwire or Beverage antenna, I doubt if you could hear a signal of that low intensity. Even with 50 kW, it would only be 11.5 uV/m. I say it's skywave, especially if you're hearing it on a Grundig, Panasonic RF-2200 or simlar radio without an external antenna.
What about higher power with a more efficient antenna?
For example, KSTP's near-Franklin antenna (two stacked 179.4° elements), which I used for reference, has an efficiency of 511.77 mV/m @ 1 km, referenced to 1 kW. The highest power transmitter I've heard of in existence is 2.5 megawatts, and if you feed each segment (total of 2) of the Franklin with its own dedicated transmitter, that would be 5 megawatts.
As the FCC figure 8 calculator won't let me calculate for Franklin antennas, I found, by trial and error, inputs that would get me a field of 1/2 the efficiency I wanted (a 72.8° antenna with 90 54° radials does 255.9mVm@1km/kw).
Then, as the calculator has a 4-digit display limit, I had to quarter the power (halving the field strength) until it would return a result (1250kW got me 9047.558mV/m).
Finally, I did the necessary doubling (to compensate for what I had to do previously), and if I did it correctly, 5 megawatts with a Franklin antenna (two 2.5MW transmitters, one feeding each segment) would have a field of 36,190.232 mV/m @ 1 km.
With a signal like that, how far would that go over saltwater until the signal is below 0.1μV/m, or whatever would be the limit of sensitivity/detectability for the aforementioned high-end receiver+antenna, assuming atmospheric noise is at its absolute minimum (for example no thunderstorms within 10,000 km or so)? I wanted to calculate it a while back using the graphs, but it was way off the graph's scale.
trusty said:
I've always wondered about the "overlap" of
WAPI in Birmingham and
WFLI in Chattanooga which are on the same frequency (1070), but only
143 miles apart. I know there are local freqs. (1340) that have extremely short spacing, and WFLI is directional, but both stations are 50kw in the daytime.
1. Anyone ever been in NE Alabama to hear any conflict on 1070?
2. Are there any other two regional AM stations that have shorter spacing than these two?
What about 1390 KLTX Long Beach, CA, and XEKT Tecate, BCN (which the sites erroneously list as being on 1380), both running 5 kW? I'll have to post a recording later, but they were both (I think) armchair copy on the barefoot Tecsun PL-606 (100mm ferrite) at the Fashion Valley trolley station in San Diego, CA.
Also interesting to me is THREE closely-spaced 1580s - KBLA Santa Monica, KMIK Tempe, and XEDM Hermosillo, all of which have 50kW nighttime skywave authorization. While KMIK is the strongest signal here in El Cajon, the others are usually present, too.
