VHF Summertime Sporadic E
(Or how to work 1500km QRP on Two Metres)
Summertime Sporadic E, or Es as itís often referred to, is one of the most exciting VHF propagation modes. This is especially true when the MUF reaches 144 MHz. Below is a guide to Summertime Sporadic E, what to listen for and how to work the DX.
What is Sporadic E?
There are three layers to the ionosphere F, D and E. We all know about the importance of the F layer to HF propagation and the way in which it refracts radio waves making world wide communication possible. The D layer and the E layer play little part in this, indeed they can have a detrimental effect to HF conditions by absorbing the transmitted signal before it reaches the F layer.
This is particularly true of the E layer when it is heavily ionised. During the summer months from May to September but in particular June and July, very intense clouds of ionization can occur. While not good for HF it does mean that VHF signals can be refracted by these clouds allowing contacts way in excess of the normal VHF range. The cause of this intense ionization is unknown and of course very sporadic in nature. But some aspects have a degree of probability and with careful monitoring of the VHF range a good indication of a likely opening can be gained. Openings are more likely to occur early in the morning, early afternoon and in the evening although they can occur at almost any time.
What to expect from an opening.
Just like the HF bands each of the three VHF bands; 50 MHz, 70 MHz and 144 MHz have their particular characteristics.
50 MHz Six Metres
Always the first band to open 50 MHz is so widely available in Europe now that it will not take long to work most countries. Usually open most days during June and July and often open all day and into the late evening. Trans Atlantic double hop propagation is not uncommon.
70 MHz Four Metres
Open less often than 50 MHz. Fewer countries have access to 70 MHz than 50 MHz but the number has increased in recent years. The scarcity of countries with access only adds to the excitement. Your next contact could be the first G to a country new to 70 MHz. Cross band contacts can be made between 50 MHz and 70MHz but skip difference is often apparent.
144 MHz Two Metres
The real excitement is to be had on 144 MHz where openings can be very brief. Itís at this upper limit of Sporadic E where monitoring lower frequencies to follow the developing MUF really pays off.
Signals can be extremely strong but sometimes also very selective; a station just 50km away may give a DX station a 59+ report but the same station maybe practically inaudible with you. A very interesting phenomena of a Sporadic E cloud is its movement, this is most noticeable at 144 MHz. During longer openings stations from different but adjacent locations come and go as the cloud moves, usually northward. This could mean that the DX you could hardly hear soon has a very strong 59+ signal giving you the opportunity to work him and someone else losing out. Justice at last!
How Does An Opening Develop?
Sporadic E propagation must be supported at a lower frequency for any to occur at a higher frequency.
Propagation may be observed as low as 14 MHz - 21 MHz. Listen for very strong near continental stations or sometimes even within the UK. As the ionization starts to built so the MUF increases. Next you may hear strong signals on 28 MHz. Ever decreasing skip length at the lower frequency bands indicate that the MUF is increasing. Try 50MHz, once again strong near continental stations may indicate that the MUF is higher. So follow onto 70MHz and then 144MHz.
While the MUF can reach 144 MHz during a Sporadic E opening its progress to these frequencies is not guaranteed.
What indicators are there, other than amateur activity, of an increasing MUF?
There are many other transmissions in the VHF range other than amateur signals that are a useful guide to the developing MUF. There are still many European countries using the Band I television frequencies and an early indication of an opening can be heard by listening for the TV carrier. In particular on 49.750 MHz and 48.250 MHz but there are plenty of other frequencies. A very useful indication of propagation to eastern European countries comes from the old 65 MHz to 74 MHz FM broadcast band which can at times all but obliterate 70 MHz. Between 70 MHz and 144 MHz the only really useful transmissions are in the Band II FM frequencies of 88 MHz to 108 MHz. Although rather crowded in the UK now, Band II Sporadic E signals are often so strong as to override even local stations. RDS can also help in the identification of the direction of propagation.
Of course these days the internet is also a very useful tool for monitoring the progress of an opening, in particular DXSherlock. Even so there certainly is no substitute to being in front of a rig ready to catch the DX when it suddenly appears out of the noise. The internet is still not able to predict when this might happen it can only show spots of past contacts.
Six Metres is open but Ten Metres is dead, why?
Sporadic E can be very selective, skip length varies between the bands, activity varies between the bands, itís common for Six to be very active and Ten apparently dead but it can only be a lack of activity on Ten, check the beacons. The same can be true of 70MHz compared to 144MHz. Neither the 50 MHz nor 70MHz band are available to all countries within range during an opening but this does not mean these countries will not be active on 144MHz.
How do I work the DX?
By being vigilant and watching the developing MUF especially if you want to catch a 144 MHz opening. It is not necessary to have a linear and a large antenna array to work Sporadic E. Signals during major openings are often extremely strong. Many stations have been worked using QRP and small aerials. But of course the use of a beam and a resonable power level will help you make more contacts.
73 and good DX