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Weak Signal VHF by Tim Marek - K7XC
Analog VHF Meteor Scatter

By Tim Marek - K7XC

Since the early days of 144 MHz "Weak Signal" VHF DXing, Meteor Scatter (MS) has been the most consistent method of making long haul contacts between 500 to 1400 Miles. The odds of completing a contact via Random Meteors (Rocks) are relatively good any early morning and increase dramatically during one of the many Meteor "Showers" that occur each year. How do I make use of this medium to work more grids on Two Meters (2M)? What are the mechanics involved? How do I know where & when to beam my signals? How do I make contacts using MS? These questions and more will be answered within this document.

What is MS?

MS is the term for sending your signals beyond the horizon via refractions off of the Ionized Gas trail that streams out of a Meteor as it burns up while entering Earths orbit. As a "Weak Signal" VHF radio amateur, we are only concerned with ones large enough to support brief contacts on 50 MHz and higher.

How does MS works?

The correct answer is "Very Carefully" all kidding aside, There are many factors that go into successfully completing a MS contact. For simplicity sake I will only deal with 2M for now. Later on I will compare the bands, their effectiveness and drawbacks. As a Meteor enters our atmosphere the friction of striking air molecules at very high speed causes them to heat up and break down, leaving an ionized trail of hot gasses behind. It is this trail that refracts radio signals, sometimes usable to as high as 450 MHz. Think of it as a long cylinder of hot gasses that once it forms begins to twist and turn until it finally dissipates. Meteors that meet the Earth head on in the morning have a higher apparent velocity then those that overtake the Earth behind in the evening, which is why Random Rocks work best in the hours just before Sunrise.

The larger the rock, the faster its apparent speed relative to the earth, the higher up it starts to burn, the longer the burn, the denser the Ionized trail, the stronger the refraction (Over-dense Burn), the longer in distance and higher in frequency it will support radio communications.

Consequently, The smaller rock, the shorter the burn, and the slower the rock the shorter the burn, The less dense the Ionization, the weaker the refraction (Under-dense burn), the shorter the distance and lower in frequency it will work.

Due to the physics involved, the minimum MS distance you can work is around 500 miles with 1400 miles about the maximum. This is all based on the curvature of the earth, thickness of the atmosphere, height at which the average meteor starts to burn, etc. This distance can be lengthened by stations on one end or another operating from a tall mountaintop, use of high power, CW (30 to 50 WPM), Linking into Sporadic E layer propagation on one end or another, a large/fast rock, etc. In 1994, I worked 1433 miles from atop 8000 Pond Peak NV in DM09 to the very NW corner of LA in EM26. He was at the kilowatt (KW) power level with a large array and heard me many times. I ran 150 watts into a 2.2 wavelength yagi up 15 at a very quiet mountaintop receiving location. In the 1 hour & 4 minutes it took us to complete, I heard a total of 5 seconds from him, but it was the right info to complete the contact.

How Do Meteor Showers Work?

Occurring roughly the same time each year, Meteor Showers are named for the constellation from which they seem to appear. They can last from only a few hours to several days or more. The more popular showers range from 10 to 20 per hour to over 100 per hour, with the occasional meteor storm that measures activity from tens of hundreds to over a thousand meteors per hour.

Using a pencil to aid in our understanding the mechanics of MS, Imagine a long cylinder of hot gasses formed as the meteor travels to earth. It falls at roughly a 45 degrees angle, so hold the pencil the same way. Looking at it head-on, it has a very small cross section. Looking at its side, the entire length of the burn adds to the cross section, providing much more refracting surface and much louder signals. This is why it is important to know the mechanics of a meteor shower, where the rocks predominantly fall from and what direction they fall towards. For example: If they traverse from NE to SW, the best radio path would be from the SE to the NW and vice versa. The weakest returns would be from head on (NE to SW).

Also, as time passes from late evening to morning, the earth is still spinning and the apparent direction of the meteor streams change in relation to your location. Moving the "sweet spot" roughly 90 degrees, or in this case from SE / NW to NE / SW, as the rocks now appear to fall from NW to SE. The earth can also get in the way causing the shower to "set" below your horizon.

How Do I Know When a Shower Will Occur?

How long the shower is visible, where it will rise and set, Number per hour, avg. speed, etc, all its typical characteristics are widely known and published many places from books and magazines to various Web sites. One of the best sources of information is to use one of the many MS prediction software packages that are available for download. A complete list of showers and software can be found at the end of this article.

I know when and where, Now What?

There are several ways to successfully complete a Analog (SSB) MS contact.

  1. Random or unscheduled contacts take place on or near the calling frequencies depending on level of meteor and station activity. When there is lots of either you will find stations +/- 20 kHz or so, when there little of either, seldom does anyone stray from them.
  2. Scheduled contacts are picked up via Telephone, Snail Mail, 3.818 MHz, Email, or one of several web sites established for the purpose of soliciting Skeds. A list of appropriate web site will follow this article as well.
  3. Tailend someone. Youre tuning around and find someone running a sked with someone else. You hang around till they finish and then start calling the station you want using the same time protocol of the station they were just working.

Whats a Time Protocol?

To minimize the chance of transmitting on top of one another (a collision) you take turns transmitting and receiving based in quarter periods of a minute. The furthest west station would transmit on the 1st and 3rd quarter minute and the eastern most would transmit on the 2nd and 4th. This reduces collisions and assures someone is always listening for your transmission. When CQing on Random Rocks I try and transmit for 5 seconds and listen for 5 seconds, starting at the top of the minute. When long burns or lots of rocks are falling, this process gets sped up considerably. Use your best judgement.

OK, I now know when but WHAT do I send? And Why?

Simply put, what you send is based on what you have heard from the other station. It also prompts the other station to end what you need to complete the contact (QSO or Q). To be considered a "Completed Contact" you must hear both calls, exchange one piece of data, and confirm reception. Stations start out sending both callsigns over and over during your 15-second period. You continue to send " Calls" until you have heard both yours and his, though they need not be in any order. Once you have received "Calls" OK, you then send calls and a report during your 15-second period. (The typical report is "S2" what dates from the beginnings of MS and stands for burns or "Pings" of 1 to 5 seconds in length. These days "S2" is the equivalent of saying "59" on HF.) If its a random contact, the best thing to send is your grid square. That way the other station know where you are and it helps others point the right way to try and work you as well. Once the other station hears calls he will send calls and a report as well. Once you have both calls and report you switch to sending "Roger Report" for the full 15 second period (Whatever your report, S2, your Grid, Whatever, is what your sending him along with "rogering" that you copied what he sent). This goes on till you hear him send "Roger". At that point it is a complete contact, but traditionally you would confirm his Roger with a stream of "Roger 73". Hearing that, he would send a stream of "73" thus letting everyone know its a done deal. In the beginning you may feel self conscious about screaming "Roger 73 Roger 73" over and over for 15 seconds but fear not, you will loose that feeling once you start working new grids! You may, as I did, become a certified crazy known affectionately as a "Ping Jockey". Youll joyfully howl strange things into your microphone into the wee hours of the morning, fighting sleep deprivation, hunger, a sore throat, and loving it!

What is MS like on other bands?

MS can support brief communications from HF through 432 MHz. As you go higher in frequency, the usable burns fewer, shorter in duration, and weaker in strength. For example, at 28 MHz a typical burn lasts a few minutes. That same burn at 50 MHz is 20 seconds long, at 144 MHz it lasts 2 seconds, less than half a second at 222 MHz and at 432 MHz yields a brief "Ping". With persistence and determination it is possible earn VUCC through UHF without the use of Moonbouce or EME (Earth-Moon-Earth).

Places to find more information on Meteor Showers

Several fine publication now exist to help you understand MS and how it can help you work distant stations using "Weak Signal" VHF / UHF techniques. Attached is a partial list of titles

VHF/UHF Handbook - Edited By G8DPS - 1997 RSGB

41st Annual West Coast VHF Conference Proceedings Edited By KK6CG 1996 - S CA 6M Club

The VHF/UHF DX Book - Edited by G3SEK - 1995 RSGB

The VHF "How To" Book By N6CL 1995 CQ

Beyond Line Of Sight Edited By W3EP 1992 ARRL

VHF Amateur Radio By W6SAI 1988 Radio Publications

VHF Handbook By W6SAI 1964 Radio Publications

VHF for the Radio Amateur - By W6AJF - 1961 CQ

Places to find More Meteor Shower Information

http://medicine.wustl.edu/~kronkg/meteor_shower.html

http://ns.ilk.de/sites/gap/ms.htm#by

http://www.panix.com/clay/ham/propagation.html

http://k7xc.tripod.com/K7XCweaksignal/

List of Major Meteor Showers

Name       Peak   Usable Days   # / Hr  Best Times(Local)   Path     Notes

Quadrantids  Jan 3rd   Jan 1-4        50   0200 0800   NW-SE  Intense Fast Rocks

                                                         0800 0900   S

                                                         0900 1430   SE

Aquarids      May 4th  May 1-6       15   0500 0600   NE-SW  Fast Rocks

                                                         0630 0830   E-W

                                                         0830 1000   NW-SE

Arietids      June 7th   June 1-15     60   0500 0700   N-S    Intense Daytime Rocks

                                                         0715 0900   NE-SW

                                                         0900 1000   E-W

                                                         1030 1200   NW-SE

                                                         1230 1415   N-S

Perseids     Aug 12th  Aug 10-14    50  2230 0400   NW-SE    Very Popular

                                                         0500 0700  E-W    Large Rocks, FUN!

                                                         0800 1300   NE-SW   Looong Burns!!

Orionids     Oct 21st   Oct 18-23     20   0030 0130   N-S        Can Be Productive

                                                         0130 0330   NE-SW   Despite Low #/Hr

                                                         0330 0500   E-W

                                                         0500 0730   NW-SE

                                                         0730 0830   N-S

Leonids     Nov 17th     Nov 14-18   15   0200 0330   N-S        #/Hr Can be in 1000s

                                                         0330 0530   NE-SW   During 33 yr peak.

                                                         0530 0700   E-W       Over 500/Hr in 2001.

                                                         0700 0900   NW-SE

                                                         0900 1100   N-S

Geminids   Dec 12th   Dec 10-14   60   2100 2330   N-S    One of the most reliable

                                                         2330 0130   NE-SW    Plenty of Rocks

                                                         0130 0230   E-W

                                                         0230 0400   NW-SE

                                                        0400 0730   N-S

That should be enough to get you started. Visit the many web pages and associated links for information on advanced MS techniques.

Best of luck!

Tim Marek - K7XC - DM09ol

Analog VHF MS