Contacter l'auteur / Contact the author

Recherche dans ce site / Search in this site

 

 

CQ DX for a SWL

The MUF and its impact on DX transmissions (II)

One of the most important parameter to take into account when speaking about long distance transmissions, but even for regional QSOs, is the Maximum Usable Frequency, MUF, the critical frequency that is reflected from the F2-layer at a distance of 3000 km from the transmitter by a single hop refraction.

It is a median value, what means that it is generally valid (or the circuit open) 50% of the time, or 15 days per month. But 50% also means that a particular day this upper frequency can be close (0%) or wide open (100%), this is thus 50-50... one day it's good, another day it's no more, and nobody can tell you what day of this month will match to the MUF.

The MUF depends first of all on the solar activity characterized through the solar flux index, SFI, which is correlated with the smoothed sunspot number, SSN.

For short, to understand how this critical frequency affects your ability to hear DX stations, I suggest you to test various setup in the very simple propagation prediction program HFProp written by G4ILO. Then you will quickly understand what's the matter with the MUF according to the time of the day, the value you give to SFI (or SSN), and in a lesser extent to Ap and Kp indices that affect high latitude propagation. Of course, you can use other propagation programs, all providing a MUF forecast, the most complete and accurate showing the MUF status at earth scale in high resolution (e.g. DXAtlas or GeoAlert-Extreme Wizard 3 that deserves your attention).

To use : DXMaps

Display DX spots visually

Propagation forecasts calculated with G4ILO's HFProp. At left, during the period of maximum solar activity, for a solar flux index of 169 (SSN 125) on March 1, 2000 at 17:00 UTC, the MUF over Panama exceeds 34 MHz and even 41.6 MHz in Burkina Faso (XT). The entire side of the Earth plunged into darkness is wide open on 20m but at that time you could probably not hear (either work) many stations from the american continent yet. At right, the same situation but at the minimum of the solar activity with a solar flux of 72 (SSN 10). Now the MUF over Panama is only 17.3 MHz. That means that at this time you might probably not hear DX stations over 14 MHz because sky waves are not reflected back to the ground; these frequencies are closed.

On frequencies from 14 MHz and up, the solar flux must reach high values to establish very long distance communications with ease. If equatorial regions display a MUF over 30 MHz like during the period of maximum solar activity, you have chance to work or hear some scarce DX entities whatever the band. On the contrary, when the same regions display a MUF lower than 14 MHz or so like during the period of minimum of the solar activity, if you want to hear far DX stations it is better to work at night on 7 MHz and down.

Propagation forecasts calculated with G4ILO's HFProp during the minimum of the solar activity on March 1, 2006 (SFI 72, SSN 10). At left the poor propagation conditions expected on the 15-meter band. Indeed, the MUF over Panama is not higher than 17.3 MHz, less than half of what it was during the maximum of the solar activity. In such circumstances only low bands (1.8-7 MHz) remain open, mainly at night as displayed at right showing the forecast for the 40-meter band with, superimposed, the MUF/LUF chart for Central Africa (XT). Note that the 20 meter band is generally open all through the sun cycle, even if we experiment more noise, degradations and a band closing earlier in the afternoon during the quiet periods of its cycle.

Seeing all these maps, it is clear that pick up DX stations is also a question of smart, for example taking advantage of propagation forecasts and checking band scope, and surely not a question of chance.

First thing to remember, propagation turns clockwise from Japan to United States via Africa to end in the Pacific ocean in respect with the Sun position. If you take advantage of this simple rule you will understand how work 50% of the amateur traffic and how to listen such or such DX. The remaining 50% concern propagation conditions, the impact of solar and geomagnetic activities on the status of the ionosphere.

Working with beacons

Another efficient way to appreciate the propagation is to listen a few minutes to propagation beacons. The ones that interest us are stations using omnidirectional antennas. They are transmitting on 14.100, 18.110, 21.150, 24.930 and 28.200 MHz.

On each of these frequencies, during three minutes and without interruption 18 stations of the NCDXF/IARU Beacon Network spread all over the world (4U, VE, W6, KH, ZL, VK, JA, RR, VR, 4S, ZS, 5Z, 4X, OH, CZ, LU, OA, and YV, cf. the link) transmit during 10 seconds their call sign in CW at 22 wpm at four power level decreasing gradually from 100 watts to 10 watts, 1 watt and 0.1 watt. Their signals are synchronized with GOS time signals. Every 10 seconds, the next beacon listed starts emitting while previously transmitting beacons setup up one bands (from 20m to 17m, etc). After 50 seconds of transmitting, a beacon has cycled through all five bands, and remains silent for 130 seconds. At multiples of 3 minutes past the hour, all 18 stations have completed the 20-m transmission and 4U1UN starts another cycle.

To help you in the field, some developers provide small applications checking beacons in real-time, while some manufacturers sell e.g. a portable device monitoring them like the MFJ-890 Beacon Monitor. But read well its specifications before buying.

To read : Review of beacon monitoring programs

Reverse Beacon Network

Real-time plots of the relative S/N ratio of HF NCDXF/IARU beacons recorded by BeaconSee thanks to a serial connection to a HF receiver connected to a dipole antenna. These recordings were made on September 2, 2004 at 14.100 MHz in CW mode using several DSP filters and a bandwidth of 100 Hz, respectively near 18 UTC (upper) and 21 UTC (below), just before and after the gray line reached my station. Before 18:00 UTC and until the gray line was gone, there were strong signal alterations (all pinky dots) while at night most emitters disappeared except in directions where propagation was still open. Signals were much clearer too.

How to work with beacons ? Let's imagine that you are tuned on 14100 kHz. Nothing, but noise... Don't be surprised if you do not heard anything at all during a few tens of seconds, sometimes longer. But trust me, in 99% of cases emitters are well active ! Listen, there is one. Did-did-did-did-daad... (4S7B).

In fact, if you are able to decode, or at least to hear, the first signal always transmitted at 100 W you are lucky; that means that the propagation in open from that country (e.g.from 4S), and for licenced amateurs with a little luck this is reciprocal and they might work that DX entity.

But conversely, if you are not able to hear the least signal during 3 minutes or more, the propagation is really closed to most DX stations and it is better to change of band or to fill out your QSLs, Hi ! Thus these beacons offer you an excellent opportunity to appreciate the propagation "live" in listening simply bands.

Parallel to beacons, you can also listen to AM broadcasters. For long distance propagation they all use the F2-layer. In using a database of AM emitters (e.g. the Klingenfuss CD-ROM) and searching for the strongest of them in different DX countries you can also get a good status of propagation conditions.

The gray line

As we told previously, for DXing the propagation on the 20-15 m bands becomes very favorable around one hour before the sunset and until about one hour after the sunrise, where euopean stations usually hear loud and clear emissions from South America (PY, LU, CE, etc) and from Asia and Oceania (YF, JA, VK, etc).

At first sight it is not specially amazing to hear them in HF bands, but after check some influencing factors appear. Amateurs can hear of work  these DX stations at sunset or sunrise because they are just on the gray line of the terminator (the line separating the day from the night), known to increase propagation via the F-layer. When I was a young amateur radio I noted that improvement, and used properties of the grayline without even knowing it !

That being said, even during the years of high solar activity, most other DX stations located over 10-12000 km away remain difficult if not impossible to hear while the Sun is not set. In this context, a good propagation program is a very helpful tool.

One of the best way for an european amateur to hear South America (CO, PY, LU), Asian and Oceanian stations (JA, YF, VK), and vice versa, is to work with the gray line. About one hour before the sunset or just before the sunrise in Europe, when DX signals follow strictly the gray line, we receive all these far countries loud and clear, sometimes 59+. Below, my home location just after the sunset on February 16, 2004 at 18:25 UTC. On the enlargement, the bright object at left is Venus. Documents Fourmilab, Living Earth and T.Lombry.

Time zones

From Europe you can occasionally hear very far DX stations located over 10000 km away from Chile, Argentina, Indonesia, Japan, Australia, New Zealand, Polynesia, etc. Their number is however reduced, but not only because they are far from your station or because they transmit from small islands on which live few amateurs. They are also more difficult to listen because they show a large time shift.

A time shift from 10 to 12 hours can be big advantage because at 1800 UTC, in summer it is 8 pm local time in Europe but already 8 am in New Zealand and in a few Pacific islands (KH8, FO, FW, T2, ZK1, etc). However it is only 2 am in Thailand (H+6), 4 am in Japan (H+8) and 6 am on the eastern coast of Australia (Sidney, H+10). These countries will be hard to work if these amateurs are still in a deep sleep... You will have much more chances to listen to these stations if you wait until noon or early in the afternoon. At 11:00 UTC in Europe (1 pm in winter) it will be 7 pm in Thailand, 9 pm in Japan and 10 pm in Sidney. Both extremes of the world have chances to work together.

In the afternoon on this December 31 in Europe, for your New Zealander contact the festive season is already over. If this amateur is probably still awake on this special occasion, in ordinary times it is not alway easy to work with such extremes time shifts.

The same is true for european stations looking for DX stations in America. Europeans amateurs have all chances to hear or work K, VP, XE, HK or PY stations late in the evening in Europe; at 2300 UTC, midnight in Europe in winter, it is 9 pm in Sao Paulo, 8 pm in Chile, 7 pm in New York, 6 pm in Columbia and 5 pm in Mexico, but it is only 3 pm in California.

Another good period is the early morning in Europe; by 0500 UTC, it is 1 am in Caribean islands and midnight in Colombia or Chile.

At these occasions you have the opportunity to listen or work tens of DX stations during a short period. So, most of the time I have worked Central and South America either late in the evening or in the early morning. Of course most of these stations are in pray to pile-ups.

In that matter, the western U.S. coast and Alaska (H-9) without speaking of islands like Hawaii (H-11) are always harder to work from Europe than any other K station. They are not only far in distance but the time shift does not help communications. In spite of the very conductive sea, their signal is much attenuated due to the distance and the Sun influence. Listen to a KL or a KH6 gives often rise to a pile-up.

Remember also the different time zones used in the U.S.A. That could help you in filling out correctly your QSL date and time group or to convert your local time in the right UTC.

First of all, note that for DT (daylight saving time) you must add 1 hr at the Standard local time, e.g. PDT = PST+1 or GMT-7. So, PST = GMT-8, MST = GMT-7, CST = GMT-6, EST = GMT-5, EDT= GMT-4. And of course, after midnight you have to change the date as well. That seems obvious but on a significant fraction of QSLs (up to 30% sometimes) the date and time group is incorrect in this regard. 

To check : The Time in the world

Download : MetaWrap Time Converter

QSO with Central America on 20 m

(heard late in the evening or early morning in Europe)

WP4MPV in Puerto Rico working EA5FWW on 20m, 20:15 UTC, June 2015

6Y5TR in Jamaica working VE1BB on 20m, 23:36 UTC, June 2015

FS4WBS in St Martin working FO5QS on 20 m (5 up), 05:57 UTC, June 2015

4V200YH in Haiti working on 40m with QRM, Feb 2004

Documents LX4SKY. Listen to more QSO.

On the other side, do no worry about the "most wanted DX", I mean all these small islands that you will maybe hear a handful times in all your amateur live like FO, FW, KH8, T2, T3, ZK1, etc.

Transmitting usually during DX-peditions, these stations are QRV 24 hours a day and work easily 5000 QSOs a day, up to 6 contacts each minute ! Whatever the time of the day, the mode and the frequency used you have some chances to hear them more than once during the pile-up if your antenna is large enough (1/4l or better) and somewhat in height. Conversely, to work those far DX is another affair...

But this opportunity will not be true with individuals calling CQ DX from their small island lost in the Pacific ocean. Contrarily to DX-peditions that use quite large antennas coupled to kW-amplifiers (not always but often), at local noon in your country, if these far stations work bare foot (without external amplification) and do not steer their antenna in your direction, their signal will be very weak if not impossible to hear due to the Sun presence and their low power. Worse, when it is night in your country most JAs, VKs and islander workers from Pacific are not back home yet.

However we cannot generalize such observations. Because at mid-way, the opposite is also true : JT amateurs for example in Mongolia can no more use the 20-m band for DXing after 8 am local time during the summer because of the Sun, and have to QSY to the 15-m band or even QRT. In Europe it is near 1 am and the QRN is usually very low and we could hear them all night long if they could still hear their correspondents. The problem is still worse with Far East countries and Oceania where the time shift means that the Sun culminates above the horizon to the remote station creating much QRN and limiting progressively the propagation to short distances.

So, in listening to ham bands, also think to the working conditions at the remote station, and try to anticipate their difficulties before to conclude that your installation is faulty or the band close if you don't succeed in listening your favorite DX entity...

First of all, be patient, and if you are really interested in picking up signals from the Pacific or from stations located at antipodes, I suggest you to invest in a directional antenna (e.g. a three element beam or 2 element quad is enough) or try to exercice your skill in CW. Indeed, many of the "most wanted DX" stations work essentially in Morse code for a simple question of reliability and ease to work DX stations, that thanks to its narrower bandwidth than SSB supports much better QRM and other noise on the frequency.

Last chapter

Working with the long path

Page 1 - 2 - 3 -


Back to:

HOME

Copyright & FAQ