CircuitJunkie
Member
- Joined
- Jun 25, 2022
- Messages
- 5
Hello All. My name is Sal. I'm a new RR member and would like to thank the good peeps at RR for letting me in. The lunatics will surely take over the asylum.
That said, I've been doing a LOT of scanning lately, reading/watching everything I, as a former ham 30 years ago, didn't have access to, when I came across a (one of many) interesting phenomena I thought would be worthy of sharing and inquiring about here on the forums.
The mystery in question arose when I was manually scanning chunks of 3.2MHz spectrum, sitting patiently, watching each slow-moving waterfall, and moving to the next chunk of spectrum in turn, just for (sick) kicks. I happened to land on a NWS broadcast, and noticed that it wasn't the familiar frequency I thought I had memorized. So I dug a little deeper, trying to optimize my settings to get the audio to sound good, and quickly gave up and moved on to the next dribble on the screen. It was a brighter signal, and lo and behold, it was THE NWS broadcast again. It started, ran for a bit, then stopped as abruptly as it started. Was this just the same repeater transmitting on one of the other 6 channels of the NWS? I wondered. I let the screen fill with dribbles and then stopped the (SDR) radio to investigate.
The first (continuous) stream was at 163.06250. This second (discontinuous) chunk was at 163.56875, a delta of 506,250Hz. I'm not a radio engineer, but I wondered: Could it be an IF stage in my SDR, but then I thought no, that would be an odd IF.
I went back for another look at the waterfall and noticed that there were chunks of signal in other channels of the spectrum that were copies of the original continuous stream, but offset in frequency and varying in intensity, some chunks stronger, some weaker, sets of the same chunks appearing at the same time on different channels, but not consistently. So let's say if a reflection chunk happened on channel "A" it would happen at the same time as channel "B", but each channel would have a stronger or weaker signal than the original continuous signal. I didn't stream long enough to see all the possible permutations that could happen over a 3.2 Mhz block of spectrum, and it probably would help to show you a picture, so I'll attach one. I annotated the screenshot with horizontal marker lines on the waterfall where I'm seeing the "reflections." You'll note that these reflections vary in intensity (signal strength) and in character (Q? or coherence or acuity or precision). The signals in some channels are more or less defined than others, something caused by weather/topography/general propagation?
Here are some of the channels. "F" denotes full or continuous streams. The "A" sets of channels correlate with one another, as do the "B" sets of channels, as well as correlating to the "F" channels. Seems simple enough to be a harmonic or reflection at first glance but if you look closely, some signals stop and start in such a way that is either mechanically controlled or whatever natural phenomenon is causing that particular reflection is discontiguous.
163.06250F
163.51875A
163.56875A
164.06250B
164.08750B
164.09375B
164.13750B
164.18750F
164.63750A
165.25625A
In any case, I was hoping someone more experienced than I might be able to shed some light on this mystery. Can't wait to hear some answers/theories!
That said, I've been doing a LOT of scanning lately, reading/watching everything I, as a former ham 30 years ago, didn't have access to, when I came across a (one of many) interesting phenomena I thought would be worthy of sharing and inquiring about here on the forums.
The mystery in question arose when I was manually scanning chunks of 3.2MHz spectrum, sitting patiently, watching each slow-moving waterfall, and moving to the next chunk of spectrum in turn, just for (sick) kicks. I happened to land on a NWS broadcast, and noticed that it wasn't the familiar frequency I thought I had memorized. So I dug a little deeper, trying to optimize my settings to get the audio to sound good, and quickly gave up and moved on to the next dribble on the screen. It was a brighter signal, and lo and behold, it was THE NWS broadcast again. It started, ran for a bit, then stopped as abruptly as it started. Was this just the same repeater transmitting on one of the other 6 channels of the NWS? I wondered. I let the screen fill with dribbles and then stopped the (SDR) radio to investigate.
The first (continuous) stream was at 163.06250. This second (discontinuous) chunk was at 163.56875, a delta of 506,250Hz. I'm not a radio engineer, but I wondered: Could it be an IF stage in my SDR, but then I thought no, that would be an odd IF.
I went back for another look at the waterfall and noticed that there were chunks of signal in other channels of the spectrum that were copies of the original continuous stream, but offset in frequency and varying in intensity, some chunks stronger, some weaker, sets of the same chunks appearing at the same time on different channels, but not consistently. So let's say if a reflection chunk happened on channel "A" it would happen at the same time as channel "B", but each channel would have a stronger or weaker signal than the original continuous signal. I didn't stream long enough to see all the possible permutations that could happen over a 3.2 Mhz block of spectrum, and it probably would help to show you a picture, so I'll attach one. I annotated the screenshot with horizontal marker lines on the waterfall where I'm seeing the "reflections." You'll note that these reflections vary in intensity (signal strength) and in character (Q? or coherence or acuity or precision). The signals in some channels are more or less defined than others, something caused by weather/topography/general propagation?
Here are some of the channels. "F" denotes full or continuous streams. The "A" sets of channels correlate with one another, as do the "B" sets of channels, as well as correlating to the "F" channels. Seems simple enough to be a harmonic or reflection at first glance but if you look closely, some signals stop and start in such a way that is either mechanically controlled or whatever natural phenomenon is causing that particular reflection is discontiguous.
163.06250F
163.51875A
163.56875A
164.06250B
164.08750B
164.09375B
164.13750B
164.18750F
164.63750A
165.25625A
In any case, I was hoping someone more experienced than I might be able to shed some light on this mystery. Can't wait to hear some answers/theories!