By Mike Otte
Abstract: A report is presented on the radio observations of the Quadrantids meteor shower. Peak activity occurred at January 3, 11h UT or solar longitude 283.00° and a possible second peak on January 3, 19h UT. Activity was so great as to provide almost a continuous reflection for several hours.
Radio meteor data interpretation is an inexact science. The direction of the antenna, the power of the transmitter, nature of the signal (analog or digital carrier), direction of the radiant, where you are relative to the rotation of the Earth and many other things influence your echo counts and meteor rates. Yet if we understand some of these spoilers of data, we can get some useful information out of the numbers.
I have been collecting Radio Meteor data for a couple decades. The collection setup has changed through the years from FM car radio to a ham transceiver to a rtl/sdr usb stick presently. I use DL4YHF’s Spectrum Lab to detect and count the meteors. Currently I use a Canadian analog TV station on TV channel 3 at a frequency of 61.259.500 Mhz.
My antenna is a 5 element Yagi pointing south and at a 45° elevation mounted on a wooden post with the reflector element inches from the ground. Aiming the antenna is not like ham radio’s “higher the better”. Keep it low. This minimizes any direct signal. I demonstrate at star parties with a wire dipole on 3 “electric fence” fiberglass supports about 30 inch off of the ground. I rotate the beam for minimum interference and no continuous carriers. J.S. Hey using radar after WWII said to aim the antenna perpendicular to the meteor’s path. So, the transmitted signal bounced back to his receiver and was detected. My case is more a compromise orientation because I am using someone else’s transmitter. So the angles will be more shallow and usually will not be directly aimed toward the transmitter.
My receiver is a Nooelec NESDR smart with a TV preamplifier. The sdr was not as sensitive as the ham radio transceiver before it. The program is SDR#.
Spectrum Lab is an audio spectrum analyzer that has the ability to run scripts that tell the program where to look (frequency or range of frequencies), what amplitude to trigger events, it can time the events, log the events, record the audio, and take snapshots of the screen. It does this 24/7/365 except when Gremlins hit. Power outages and SDR# quitting plague me.
Every hour, Colorgramme RMOB by Pierre Terrier reads the data file recorded by SpecLab and makes it into little colored squares representing the counts per hour. Then it sends them into RMOB.org for display to the world wide web.
The data I record hourly is: meteors counts, meteor counts lasting > 2 sec, accumulated refection time during the hour, meteor counts below the carrier, meteor counts lasting >2 sec below carrier, accumulated reflection time. This second set of data below the carrier is usually not very active but during showers it must have additional stations that it detects.
Here we can see a nice representation of the Quadrantid meteor shower. It actually started a couple days before and lasted a couple days beyond which is “sharp” for meteor showers.
I am assuming you know about “diurnal variation” which is the rotation of the Earth that hides you from the meteors during the evening, accelerates you into the stream during the early morning, and holds you in the stream during the day till evening again. This “diurnal variation” is a good indication of valid data. Because of my position on the Earth, I should have a good view of the peak of this shower.
So, the glaring bad data is on day 3, between 8h and 14h. Time is in UT (Universal time). I live a few miles before the 90° west meridian, so day break is about 12h00m UT or 6am local. Why is the peak of the shower showing low counts indicated by the light blue squares? So, I am counting in a band of frequencies about 200hz near the carrier. There are so many counts that they over lap and give a continuous reflection like if these are one.
In Figure 2 you can see how crazy the meteors were. The numbers on the screenshot with a comma in are the meteor counts and the duration (rough time in sec, loops in the program). I take a screenshot at the end of the hour so I can recreate the data in case it forgets to reset counts sometimes. Along the right side, you see the effective reflection time for that hour (here again it is approximate).
Another problem on the Colorgramme chart is the blue square on day 3 hour 22. This was a software shutdown of the SDR# program for no apparent reason.
The third problem on the Colorgramme chart is in the 5th day 12th hour when we had a power outage because they were deicing the power lines.
So now let’s look at the data on line charts and see if we can locate the peak better. Looking at Figure 3, the green line (refection time in minutes/hour) shows the peak but again it is flat topped with maybe two peaks that are more apparent in the numeric data. Disregard the “teepee” on the mountain. That was the SDR# quitting. The red line represents the counts and the yellow shows the counts over 2 sec long. Neither looks useful here at this time. They dipped when they should be peaking.
In Figure 4 is the data that I normally do not submit. These are the counts in a 200 hz band below the carrier frequency where there may be other transmitters.
I hardly ever look at this data because usually there aren’t many counts. Here though, it looks like I have a clear peak at 11h00m UT (λʘ = 283.00°) and a smaller second peak at 19h00m UT (λʘ = 283.34°). There are two inflections on the main peak which may indicate “strands” and the second peak has a small increase after it too. This indicates the meteoroid stream is not homogeneous. So, the narrow peak is about 7 hours wide and the Earth travels this distance: 7 hours × 108000 km/h = 756000 kilometers.
Looking back on Figure 3, you could think that during the peak when the counts should be going up they actually go down. In this inverted world the deepest valley should be the highest peak and this valley lines up with the results from Figure 4.
Radio Meteor Astronomy is a nice pastime that allows one to “see” meteors during the day and when it is cloudy in addition to night time. Living in the Midwest US, 60% of the days are cloudy. I submit data hoping some scientists can make use of it.
The Quadrantids is one shower that I think I have not seen any meteors from visually. Winter is cold and cloudy here. It is a stream of debris that Earth bumps into every year. As we get closer to space travel again, knowing where the debris lies will help us avoid it.