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The August 1994 issue of Six News
Thanks to all of our authors since 1982!



monitoring 30-50MHz across the pond
by Bob Cooper ZL4AAA.
First printed in October 1991 with extracts taken from The 50MHz DX Bulletin Vol 2 Issue 18.


from Europe...

With no North American television carriers below 54MHz, Europeans attentive to 6m possibilities must rely upon frequencies well below 50MHz as propagation indicators. With few exceptions, these are 2-way (typically FM) services including repeaters operated by private businesses, municipal authorities and public safety (ie., police, highway patrol) organizations. Few of these accumulate anything like 10% transmit time, which means you might be parked on 47.88MHz for an hour hearing only six total minutes of transmissions, even with propagation. And that six minutes total could be in 20 - second bursts. It is therefore best to keep the tuning dial moving, manually scanning a 2/5/10MHz spectrum searching for these brief, infrequent transmissions.

North America 2-way in this region is normally spaced in 20KHz steps. e.g. 35.02, 35.04 and so on. Many systems in Latin America are offset from this 20KHz step arrangement by customized amounts, e.g. 40.345MHz. They did this to reduce skip-QRM. Most such systems stand out not only by their offsets but because of their language, Spanish or "Caribbean English".

Pagers in the U.S. with their mixed voice and digital tone signalling, run high power and high activity. These pagers constitute important first-level propagation indicators. Some frequencies have several dozen different transmitters spread from Maine to California. If you have propagation to two or more transmitters simultaneously on one channel, that channel will be active more than 90% of the time. These pagers group into two frequency "bands": 35.20-35.70 and 43.20-43.70MHz. In both cases, there are a few additional channels above and below these limits. Frequency loading of any channel varies, as does transmitter power.

The best channels will vary depending on the listeners location and on the type of opening. In general, for European listeners, the following are the key channels:

35MHz Band: 35.24, 35.58, 35.20, 35.22, 35.54
43MHz Band: 43.20, 43.54, 43.42, 43.58

The 35MHz range is also used in the "American Caribbean", ie, Puerto Rico, US Virgin Islands (e.g. St.Thomas on 35.34). Those in P.R. speak mostly Spanish with some English (e.g. 35.08, .14, .24, .26, etc.).

While it is possible to individually identify these transmitters (FCC rules require ids at 10-minute intervals, most use 20 WPM Morse for this purpose, e.g. KMA234), in a practical sense you are likely to simultaneously hear several (to a dozen or more) on such a channel, making identification very difficult. Even if you do verify the call letters, a current, complete listing of such transmitters is lacking.

Instead you can derive propagation information from the simple presence or absence of activity. Hearing only one station/service on a paging channel does not suggest much in the way of a widespread opening. As the MUF rises, you will hear first one, then many on each channel. An early time for first fade-in may indicate that the MUF will rise especially high. If signals peak in strength then gradually drop, it may (but not necessarily) indicate that MUF has risen far above that frequency. Finally, if signals are free of fading, it may be a better sign than QSB ridden signals.

Other services above 44MHz generally have occasional, brief transmissions. They use 20KHz steps all the way up to 49.98MHz. Several thousand such transmitters exist between 44 and 50MHz, each with its own callsign and method of conducting business. There are no beacons or particular reference channels nor specific stations to guide you. (During the 1988-1992 F2 Trans-Atlantic DX seasons 44-50MHz was often full of North American signals. It was very interesting to watch the rise in MUF. Strong signals could be copied at 47MHz for hours on end, day after day. Only around one in ten of these openings continued up to 50MHz. I found the quicker the rise in MUF the more widespread and intense the opening would be. At times one could "follow" the climb in MUF from 44 through 50MHz in just a matter of a few minutes. (de G0JHC.)

At your location, you will gradually discover certain sources which you hear more often that others (e.g. Louisiana/Texas oil-rig crews on 48.98; WSN906 Puerto Rico on 49.58). These if written down for reference become your own warning signals at your QTH alerting you that a particular path may be about to open. It's not necessary that you know exactly who or where they are, only that you hear them just prior to 6m openings.

Above 45MHz, around 25% of those signals will be repeaters; we assume you typically hear the output since they are better situated and run more power than transmitters on the input. Some transmitters sound like repeaters but are actually remote bases, i.e. receiving input from a point-to-point link or even via landline. If you hear a squelch tail, you have a repeater. But some tails are so short as to not be evident, so tail-less signals may still be a repeater. If you are hearing both sides of a conversation, check the relative signal strength of the two sides. If it differs, you are hearing multiple transmitters; if not, it's probably a repeater.

One important factor to keep in mind is the relationship between the size of the footprint and the location of the peak MUF, relative to your listening frequency. Picture an iceberg, with only a small tip protruding above 50MHz. This tip may only cover an area of a hundred square kilometers, meanwhile the portions below the 50MHz ""waterline"" occupy huge areas. The tip may be rapidly changing in location, without noticeable motion of the large sub-50MHz portion. Meanwhile, the peak MUF may be rising and falling, again without being noticeable at, say, 47MHz. That these detailed changes are (by present methods) totally unpredictable is of course part of the six metre magic. Just don't get so side tracked in listening to indicators that you fail to catch a 60-second 6m opening as the footprint sweeps past!

Meanwhile...from the North American side. Monitoring 30-50MHz.

The following observations were made during
the CU3/K6EDX operation in June 1989.

Possibly because of European TV channel E2 (48.25 nominal video carriers), virtually the only signals heard above 45.0MHz are either the TV carriers (with sidebands) or cordless telephones. These wireless wonders are of some interest because they are heard without the 48 and 49 region, even from Portugal and Spain where E2 TV operates. European 2-way radio in this part of the spectrum is utilized very lightly by comparison with North America. The total lack or near total lack of any signals from the U.K., Netherlands, Scandinavia, and others was an eye-opener. That's not good if you are in NA and hope to walk the MUF upwards from 30 to 50MHz. 30-50MHz 2-way radio is alive in France, Spain, Portugal and perhaps Italy, but unlike the NA assignments, each country appears to have grouped its licensees (one assumes they are licensed) into relatively narrow chunks of the spectrum. Only marginal use of the same chunk of spectrum by more than one European country was observed. This may be the result of a little publicised intra-Europe agreement, an accident, or simply coordination on an ad-hoc basis. It could also be an observation error on my part.

In France the pagers signalers and repeaters are grouped between 35.000 and at least 36.025. The original channels were spaced 25KHz apart but some of these have been split to 12.5KHz channels (e.g. 35.0375, 35.1125, 35.2875). No other French 2-way was heard above 36MHz, apart from a possible 42.720 AM 2-way service and one FM 2-way at 40.2175. No cordless phones were heard from France (but see the In Band section that follows). There are no E2 videos in France, nearby there are three in Germany and one in Switzerland. Also in France there are L-2 TV audio signals on 49.224 and three on 49.250MHz).

In Spain, beside the video indicators, there is a scattering of 2-way between 40 and 45MHz (e.g. 40.45 repeater - police? 40.50 base/mobiles; 42.975 A0 + telephone). Spanish 2-way is seldom heard below 40MHz (exception 39.275). There are many 45-50MHz FM (and a few AM) telephone-family systems (e.g. 45.18, 45.24, 45.96, 46.15, 46.68, 47.1, 47.28, and some within the 48/49MHz TV band.

In Portugal, there is a surprising number of 2-way systems. Lowest is 37.54, apparently a repeater. Higher are a 38.26 repeater, 39.90 repeater, plus a lively group between 40 and 41MHz. These seem to be the best bets for serious sub-48 signals.

Repeaters: 40.14, .16, .18, .20, .22, .54, .60, .64.
Simplex: 40.06, .14, .16, .18, .20, .22, .24, .26, .34, .36, 41.175, .65, 42.65.

Note that these are spaced 20KHz between 40.0 and 41.0 and 25KHz above 41.0. Some FM and AM telco units appear in the 47-49MHz range.

From Italy, only a handful of Italian 2-ways were identified from CU3. This is despite being within 2-hop Es range and working some 60 Italian 6m stations, and hearing Italian cordless phones and studio transmitter links in the 45-50MHz region. Bad luck? I doubt it. Now, I wonder from where did the more than one dozen 40-49MHz Italian speaking channels come, which I heard in New Zealand in February-April 1991. The time frame and antenna direction never gave reason to question that Italy was their origin point. Could they be in North Africa? Lots of Italians living and working in perhaps Argentina, or Brazil? Or perhaps some unexplained failure of the 2-way signals to stand out on Sporadic-E (well EE) when they did very nicely on F layer?

Italy has no 48.25 TV transmitters, Switzerland on 48.2501 is the nearest along with Austria on 49.7501. Middle and southern Italy are far enough from either of these that you could hear the 50MHz signals (from Malta) all alone (i.e. possibly without 48/49MHz video carriers). With that as a backdrop, here is what could be identified from Italy in CU3, combined with those mystery 40+ MHz channels logged earlier this year (1991) in ZL. Note that as in Portugal, the systems appear to be 20KHz spaced below 41MHz and 25KHz above.

AM, possible 35.22 AM, 35.55 tone call/signaler (all CU3), 40.24 2-way (CU3), 40.54 (CU3), 41.10 2-way (CU3 and ZL), 41.28 2-way (ZL), 41.26 2-way (ZL), 41.55 repeater (ZL), 41.90 repeater (ZL), 42.80 repeater (ZL), 44.375 2-way (ZL).

These five are all Telco links (CU3); 46.125, 46.277, 46.40, 46.65, 47.40. Then 48.25 and 48.275 telco links (ZL), 48.85 wideband FM broadcast link/STL (?) (CU3), 49.73 telco link with bleeper tone when not in use (CU3), 49.74 telco link with rotary dial (CU3), and 49.75 telco link (CU3).

In-Band Signals

Sync-pulse video modulation sidebands associated with strong signals in the 48/49MHz region propagate within the 6m band whenever the MUF reaches 50MHz between you and a distant TV transmitter. This Sync-pulse QRM, which sounds like buzzing carriers typically spaced about 15.7KHz apart, make listening difficult at times. Sitting in CU3 and listening to these wonderful artifacts for tens of hours inside the 6m band suggests to me that 50.110 is ill-chosen. It can be difficult to find a hole any place above 50.000 when there are several TV signals propagating at the same time, but 50.110 is, on a scale of 1 to 10, a 10 for poor positioning. As a practical matter, you in NA may get clobbered with the TV crud while the guy in Europe (not next door to such a transmitter) finds 50.110 quite clean. The net result is that he hears your call on 50.110 and answers, and you don't hear him in the crude. Suggestions? No suggestion is going to change 50.110 worldwide, but 50.105 and 50.115 were (by observation) far cleaner on average than 50.110. Those working into the Americas and other NTSC video-standard regions should also be aware that operating in the sector 50.111-114, should be avoided because of the 14th harmonic of the "colour-burst" frequency, which is normally 50.11363MHz.

Two in-band carriers have mystified 6m DX'ers for years, one at 50.024 and the other at 50.100, both are reported sometimes as A0 (unmodulated carrier) and sometimes as a tight cluster of tones. The general consensus is that they originate in SW France. On several days between 1500 and 1900 UTC I heard modulation on the 50.100 signal: FM just slightly wider in deviation than my IC575H could handle. It was broadcast programming in French, I suggest a studio-transmitter link, possibly between a remote studio and a main studio for a pop music format station. I never heard any modulation on 50.024. Both carriers sound like 25-100 watters. (Canal Plus links? de GJ4ICD).

On strong F layer propagation there are likely to be many other in-band signals as well, especially between 53 and 54MHz (a subject I will ignore for now). These include FM at 50.050, originating from France and elsewhere (the French military is assigned 50.000, .025, .050, and .075 for FM communications).


Few of us have linguistic abilities, and unless you hang around 15MHz SWBC services a bit, telling the difference between say, Spanish and Italian in a noise laden signal can be difficult. CU3AK, a friend who is an 11-metre nut in the Azores (where it's legal), assisted me in preparing a list of the "over" word as commonly used by people on the radio.

The theory is that if you can listen for the last word in a transmission (where an American might say "over"), you might get a clue as to the language from the sound of that word. There is no guarantee that a police dispatcher in Barcelona uses the common Spanish word for over, but it is a start.


English: Over
French: Ter-min-ay (or ter-min-ee)
Spanish: Cam-bee-o
Portuguese: Es-coot (or es-coot-tow)
Italian: Fin-e-tow
Italian alternatives: Tear-me-not-tow, Tay-tay

Some European 2-way systems use an "over beep" as well. Anyone who can add to this list (Russian, Chinese, Korean?) is invited to do so. There you have it, several ways to analyze what you are hearing to prepare you for working across the pond. Now if the ionosphere......

More Indicators

In Central and South America, a few FM broadcast transmitter links operate below 50MHz, and are especially useful for MUF checking due to their long hours and high power. Gord VE3KKL recently discovered one on 45.475MHz, Colombia, 47.90 Chile and 48.63 Argentina.

UKSMG Six News issue 37, April 1993


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