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Strong Signal |  |
Weak Signal |
Each beacon transmission occupies a ten second time slot. 18 beacons from different locations around the world take turns making 10-second transmissions, in a cycle that repeats every three minutes 24/7/365. This process is happening simultaneously on 5 HF bands.
Each rectangle in the display contains 8 narrow vertical "slivers" (10-second time slots) that represent eight successive samples of the same beacon 15 minutes apart. The entire display of eight successive 15-minute passes of all five bands represents the past TWO HOURS of HF activity.
When the beacon signal is strong, it has a distinctive triangular shape.
(You are seeing the initial 100 watt transmission, and then the following 10W, 1W
and 0.1W one-second tones.) When the beacon signal is very weak, you may only
see the initial 100 watt part of a beacon transmission as a single dot. The successive
time slots then appear as a string of dots.
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Strong Signal | |
Weak Signal |
The vertical height of each box represents a frequency span of only 100 Hz. The exact radio frequency of either the transmitter, the receiver, or both can drift over time. As a result, the plot of successive transmissions from a given beacon can be either a straight horizontal line, slope upward or downward, or curve as the relative frequencies of the transmitter and receiver change over time.
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Frequency drift up, then down over two hours. |  |
Very stable TX and RX freqs - less than 5 Hz combined drift over an hour and a half. |
Background noise on HF frequencies typically increases when the frequency is open for long-range transmission. If the rectangles for a given band are solid blue, the band is completely closed. If grainy noise "speckles" show in the box, the band is open to somewhere, though possibly not to a given beacon location. If part of each box in a row is noisy and part is solid dark blue, the band in question has opened (or closed) within the last two hours. (Presence or lack of noise will normally be seen in all the boxes for beacon locations on a given band.)
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Band open but no beacon heard, then closed about an hour and 15 mins ago. |
Spots or streaks that show as a continuous line in multiple boxes side-by-side on the same band are not beacons. They are random continuous noise, or other transmissions, that span more than one time slot. Actual beacons only occupy a single time slot, and will be different for each box.
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Continuous constant-strength signal(i.e. local), probably from a computer. Note constant stable clock above, and drifting switching power supply birdies below. |  |
Blast of noise from electric kitchen mixer that spanned 30 seconds (3 time slots). |
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CW operation within passband of beacon scanner during one three minute pass of this band. |  |
Receiver glitch generated by FT-100 when jumping from one band to another. |
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