Years ago, I was involved in meteor scatter operations on VHF. What is that?
Dočítate sa:
Meteor scatter
Meteor scatter on very high frequencies (VHF) is a method of communication that uses the ionized trails left by meteors in the atmosphere to reflect radio signals. This phenomenon enables radio communication between stations that are otherwise out of direct line of sight, typically at distances ranging from 500 to 2,200 km.
How does it work?
Meteors and Ionization
When a meteor enters the Earth’s atmosphere, usually at an altitude of 80–120 km, it heats up due to friction with the air and leaves behind an ionized trail (plasma).
This trail acts as a temporary reflective layer for VHF signals (typically in the 28 MHz to 432 MHz bands).
Signal Reflection
A VHF signal transmitted toward this ionized trail is reflected off it and reaches a receiving antenna at a distant location.
Duration of Reflections
Ion trails from small meteoroids (so-called sporadic meteors) last only fractions of a second to a few seconds.
During major meteor showers (e.g., the Perseids, the Geminids), reflections may be longer and more frequent.
Applications and Techniques
Meteor scatter is most commonly used on the 2-meter (144 MHz) and 6-meter (50 MHz) bands. Communication typically proceeds as follows:
Modes
Since the reflections are short, digital modes such as MSK144 (within WSJT-X) or fast CW (Morse code) and SSB are used.
MSK144 is popular because it effectively decodes signals in extremely short reflections.
Time Windows
- Connections are more frequent during meteor showers, when the frequency of meteor appearances is higher.
- However, sporadic meteors allow for contacts year-round, especially in the early morning hours.
Synchronization
For a successful contact, stations agree on a frequency and time (usually via amateur radio forums or chat rooms, e.g., ON4KST).
Advantages of meteor scatter
- It enables medium-distance contacts that would otherwise be challenging for VHF.
- It is not dependent on the state of the ionosphere like the E-sporadic layer.
- It allows for experimentation with the physics of reflections.
Disadvantages of meteor scatter
- The short duration of reflections requires precise synchronization and appropriate techniques.
- It requires patience and specific equipment (high power, directional antenna).
Meteor scatter 15 years ago
VHF setup used in the past
Back then, contacts were made in FSK441 mode, which I ran using the WSJT program. I started with a 7-element DK7ZB Yagi and a power amplifier with a KP920A, which delivered about 75W. Later, I used a power amplifier with a RE025XA, which I drove to approximately 200 to 250W.
The first contact I made this way was with LZ1KWT. This is what the echo sounded like during an FSK441 contact with that station.
Meteor Scatter Today
With the Geminid meteor shower approaching, I decided to give meteor scatter another try. About a week earlier, I had installed and configured the MSHV software to work with my Kenwood TS-2000. As part of that, I saw FT8 operation on HF for the first time (and hopefully the last).
I have a number of antennas for 144 MHz:
- a 3-element DK7ZB yagi
- a 6-element YU7EF yagi
- a quad of 5-element DK7ZB yagis
- a quad of 6-element DK7ZB Yagis
- a pair of 8-element DK7ZB yagis
A total of 69 elements, but none of the antennas are installed at my home QTH. Due to a lack of time, I didn’t get around to setting up any of them in the garden until Saturday, December 14. By then, the peak of the Geminids was already behind us. A set of four 5-element DK7ZB Yagi antennas was set up in the garden. During the evening, I began monitoring and receiving the first transmissions from stations operating in MSK144 mode.
MSHV with a received transmission from LZ1DX
The reception looked promising, so I contacted Ned LZ1DX to request a sked. Although the distance of 929 to KN22TK is relatively short for meteor scatter, my main goal was just to test things out. We started the sked shortly after 10:30 p.m. I was also listening to the signal with my ears. The MSK144 signal sounds like this:
After a few transmissions, I hear a strong burst. I reach for the mouse to enter the report and switch the transmitted message… and I see that MSHV has already set the report and even changed the message! That was a bit of a surprise. So the program handles the connection all the way through without any operator intervention. Apparently, it would even log it (if a logger were connected). I definitely need to familiarize myself more with MSHV. Peťo OM8WG, who has much more extensive experience with this mode, also sent his regards via the ON4KST chat. Hopefully, I’ll be able to install a permanent 144 MHz antenna so I can participate in this mode regularly. Setup used on my end: MSHV connected to a Kenwood TS-2000, HA8ET LNA, and 90W output via a 12m ½” coaxial cable to a 4×5-element DK7ZB yagi.
