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Working inospheric scatter on 50 Mc

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DX when the band is dead.

Say, just how does one work that ionospheric scatter?" In past months the writer has been asked this question often. Many v.h.f. hams have read something about ionospheric scatter, and developed an interest in it, but have never really given it a try. They wonder if one must have a kilowatt to get into the game, or if a hundred watts will work. They wonder if one can use medium speed c.w., or even phone, or if scatter is strictly a 35 w.p.m. c.w. man's game. This article was written to answer some of these questions, and to try to get more v.h.f. men active in this intriguing phase of 50 Mc communication. Picking up a new state or two, gathering a few extra section multipliers in a QSO Party to beat out the local competition, or just the thrill of working DX under normal conditions - these should be enough to give many v.h.f. men the urge to try scatter work on 6.

It might be well to begin with a few definitions. The terms meteor scatter and ionospheric scatter, often used interchangeably, do not mean the same thing. Meteor propagation is the burst-type of communication which avid two-meter men use to work new states during meteor showers. This type of signal is reflected from one specific spot in the ionosphere for each "burst," i.e., the ionized meteor trail. (See Fig. 1.) This phenomenon is similar to sporadic-E reflection, except that the reflecting medium is rapidly appearing and disappearing meteor trails, instead of a more permanent ionized cloud. If the meteor trail is ionized sufficiently to reflect the signal at the required angle, the received signal, in all likelihood, will not be very weak. It may not last too long, but even with less than 100 watt, the signals often reach S9 on 50 Mc, and 144 Mc pings and bursts may be many decibels above the receiver noise.(1)

Fig 1
Fig. 1. Meteor burst signals are similar to sporadic-E skip in propagation path, bvt they last only as long as the trail is sufficiently ionized, usually not more than 20 seconds or so. Even low power may produce readable signals at the peak of the reflection.

On the other hand, true ionospheric scatter signals are not reflected from any specific spot - they are truly scattered. (See Fig. 2.) Multiple reception paths exist frequently, causing signal levels to vary tremendously, with fast, fluttery QSB. These are the signals that are there when high power and good antennas are used, regardless of weather, solar, or meteor-shower conditions.

Fig 2
Fig. 2. If enough power is used o signal of readable strength is scattered from the ionosphere. Multiple reception paths are frequently apparent, causing rapid fading. Since the irregularities in the ionosphere that cause the scattering are always present, a consistent though weak signal is always available.

What kind of equipment?

You can work meteor skip on 50 Mc with 50 watt - and don't let anyone tell you otherwise! The writer has had many meteor QSOs using approximately this power, especially during the better showers.' The more power you can put on, the more consistent your scatter QSOs will be. It is unlikely that powers under several hundred watts will produce the "background signal" of true ionospheric scatter, but if you rely on meteor propagation only (i.e., signal audible only on bursts), much lower power may be used.

In any event, the signal should be clean. This means no drift, no chirp, and no frequency modulation. Don't settle for anything less than a true T9X! Be sure to check your keying for clicks; bad key clicks can be as hard on your neighbors as overmodulation splatter. But don't make the keying too soft, either. The received signal will sound soft, anyway, because of the flutter. And remember, the lower your e.r.p., the more attention you must pay to these details. It is surprising what you can do with a clean 100 watts of r.f.

Reception of weak signals on 50 Mc. does not require a converter with an extremely low noise figure. Man-made noise is the limiting factor in urban areas most of the time. Even if a location is free of man-made noise, random "antenna noise" will be audible without going lower than about 5 or 6 db. in noise figure. There is only one way to make sure that your converter is good enough for your location: at a quiet time of day, disconnect the antenna from the converter and replace it with a carbon resistor equal to the line impedance. If the noise level is noticeably higher with the antenna than with the dummy load, then your converter passes the test. At the writer's location, which is not a particularly noisy one, 2 to 3 db. of antenna noise can be heard with a single 6AK5 r.f. stage in the converter. Lower noise figure would not help, and more gain would only make it easier to overload the mixer.

The receiver following the converter does not have to be in the 75A-4 class. It should have good stability, and have a crystal filter, Q multiplier, or other means of obtaining fairly good selectivity. Restriction of the audio bandwidth is also helpful.(2)

The answer to the question of antenna size is similar to that of power level - the larger, the better - but you can get away with using something less than the best. From the writer's experience and correspondence it appears that long Yagis and stacked arrays with similar forward gains yield similar results on scatter. We don't want to start any arguments; you can believe this or not, as you wish. Just remember, you can't make them too big.

Remember, too, that although you don't need a full kilowatt, and you don't need the world's best receiver, and you don't need to have stacked long Yagis, if you compromise in too many places simultaneously you may compromise yourself right out of the scatter picture!

How to communicate?

The actual method of exchanging information with the other station depends largely upon the power used and upon personal preference. As implied earlier, you won't get much of a true scatter background signal with powers under 300 watts or so. Therefore, if you run less than this, you should make your plans so as to make the best use of meteor bursts. This means that you want to get as much information as possible across in a short time. Consequently, medium-or high-speed c.w. will certainly help.

Low Power - You won't get much in the way of results by firing up your 100 watts and 4-element beam and calling CQ DX when the band is dead. Your best bet is to write to a 50-Mc. man in the area you want to work into, who you know is active on c.w. Set up a definite schedule with him, and use timed transmissions of one minute each way, or whatever you prefer. Be sure that you can spot each other's frequencies closely, for you won't want to waste any time tuning around. To make the best of short bursts, use keying speeds of 15-25 w.p.m., if you can. You will have to repeat plenty. Something like " W0XXX de K2ITP SNJ SNJ" repeated over and over has worked wonderfully for the author in QSO Parties. Even with low power, sooner or later (usually within 10-20 minutes) there will be a good burst, and your message will be copied. Repeat the process to get your "R's" across, and you've got a new section multiplier, or state, etc. It won't be the quickest QSO in the contest, but if it puts you one section multiplier up on the local competition it will be worth the time spent.

High Power -Suppose, on the other hand, that you're running upwards of a half gallon, and have stacked antennas or a long Yagi. Then you should have a bit of that consistent, fluttery background signal. Keying speeds will not be so important. At times 10 w.p.m. may be more copiable than 25 or 30, for it may not be "chopped up" as badly by the fast QSB. This, however, depends a great deal upon individual operators.

Timed transmissions will still be helpful, although if you find that your signals are audible most of the time, you can be much more lenient about the timing. The other guy will know when you sign, anyway.

You'll still need to repeat a good bit, unless you're better than the writer at copying fluttery signals. But now you have the satisfaction of knowing that you have set up a really consistent path for QSOs, regardless of band conditions for other types of propagation!

Voice and Scatter - It's a lot harder than using c.w., but you can use voice on 50 Mc. scatter. Quite a few phone QSOs have been made during the better meteor showers between stations running fairly high power. One good system is to repeat each sentence three times; with a little luck, fairly solid contacts may be made.

Getting rid of the carrier and one of the side bands helps a great deal. The writer recently made a series of weekly s.s.b. tests with W4IKK and W4RMU, in addition to our regular c.w. schedules. These tests were made in non-shower periods, when the band was dead. Power was 500 watts indicated d.c. input on s.s.b., and 700 watts on c.w. The s.s.b. was not copiable for the percentage of the time that the c.w. was, but plenty of calls, signal reports, "Good mornings," etc., were copied on s.s.b.


So, let's get out the key, write some letters, and give this 50 Mc. ionospheric scatter a try. Even if you aren't a contest man, and already have all the states within 1200 miles, it can be a lot of fun. This business of working 600-1200 miles without waiting for the band to open bears looking into, and you can do it!


  1. For a detailed description of meteor propagation, and a calendar of Meteor Shower Data, see Bain, "V.H.F. meteor scatter propagation," QST, April, 1957.
    Ionospheric scatter fundamentals were discussed by Moynahan in QST for March, 1956.
  2. 0'Hern, "Simple low-pass filter design," QST, October. 1957.

Joe Taylor, Jr, K2ITP.