This is one of a series of “Notes” I published on Facebook. Since Facebook has discontinued the Notes feature, I am publishing that series here on my blog.
To the DX minded VHF weak signal operator, every contact beyond everyday range is exciting. This is a different world from the HF bands where long distance contacts can be made at almost any time. On two meter SSB or CW, contacts to 200 miles with a modest station and up to 500 miles running high power and a good long yagi antenna are about the every day limit. Beyond this, we need special propagation, which can take several forms: tropo, aurora, meteor scatter, sporadic E. Tropo can theoretically be any distance but only in very rare or special situations can one make contacts beyond 1000 miles or so. The ionospheric modes (aurora, meteor scatter, and sporadic E) have a rule of thumb theoretical maxium distance of 1400 miles based on path geometry with average height of the ionospheric E layer where the reflections take place. Rarely will you work anything beyond that distance, and when you do, sporadic E will probably be responsible. The fact that DX opportunities are less common at VHF is one of the things that attracts some people to it. There is a certain thrill and satisfaction in doing the unusual, the rare, beating the odds.
Many two meter DXers say sporadic E (also known as Es and E skip) is the most exciting propagation mode of all on the two meter band. It sure does get one’s blood pumping! For one thing, this propagation is quite rare at 144 MHz. Just catching one of these openings is an accomplishment. There may be years with a half dozen openings during the late May to early August season, but there can also be years with none at all. When it does occur, sporadic E propagation comes on suddenly, often producing very strong signals. Even with QRP it is sometimes possible to make 1200 mile contacts with ease. I once worked a station in South Carolina who was using a two watt portable transceiver with its built in whip antenna. He was booming into Maine! Openings can last from a couple of minutes to a couple of hours. The casual VHFer is likely to miss most of the openings that do occur. Those who monitor internet propagation reporting sites and/or have their own MUF monitor are are more likely to catch these rare openings.
I usually monitor conditions closely during the season but on the afternoon of June 13, 2017 I had been distracted. I walked into the shack in the late afternoon to find this in one of my browser tabs:
“VHF Propagation Map” uses APRS signals to map two meter openings. This is a classic sporadic E footprint. This site can be found at http://aprs.mountainlake.k12.mn.us/
Wow! I was probably missing a sporadic E opening! Hastily turning on the equipment I heard KE4TWI in Tennessee calling CQ. He wasn’t particularly strong and did not hear my low power call while waiting for the amplifier to warm up. Hearing no other signals I thought I had missed the opening. In fact I did miss an opportunity to work Tennessee and quite possibly further west to Missouri or other states. I began alternating between calling CQ on or near the North American SSB/CW calling frequency, 144.200, and tuning around looking for signals. I was about to give up when one of my CQs was answered by KD4ESV in Florida! This was a very good one, as the distance is 1436 miles. The opening would last for about an hour, but with relatively few operators aware of it I worked only four stations: KD4ESV (1436 miles), WA4GPM (1251 niles), N4TUT (1334 miles), and N4TWX (1283 miles). Nevertheless this was extremely exciting stuff! I was on two meters for more than 20 years the first time around. In all those years I worked beyond 1400 miles just once – to the Florida Keys on extremely rare double hop sporadic E, a distance of slightly over 1600 miles). This was only my second QSO past the “1400 mile wall” without using the moon as a reflector. Coming shortly after my return from a 10 year break it was especially thrilling.
This map shows some QSOs which were reported via the DX clusters. My 1436 mile contact with KD4ESV is shown. We can see contacts from southern New Hampshire to Tennessee and Missouri duing the part of the opening I missed. This map came from https://www.dxmaps.com/
The above map is one of several useful online resources for spotting openings, but it only shows contacts after they have occurred and been reported. Hence there is a lag, and since these openings can be short, in and of itself this is not the best way to spot openings. DX Maps also offers a real time Es MUF map, which may be more useful with a few caveats. The MUF map takes reported contacts on lower frequencies, such as six meters, then computes MUF based on distances and path centers. Suddenly rising MUF over 100 MHz can be an indicator of possible upcoming two meter openings. This is not foolproof. Some operators don’t report (or incorrectly report) the type of propagation when sending DX cluster spots. This can introduce erroneous data to the system, causing unrealistic MUFs to be reported. It can also miss some openings if not enough people are reporting QSOs from lower bands. Nevertheless it is very useful, especially since it can often give an early warning as the MUF starts to shoot up.
The Es MUF map was captured *after* the two meter opening, as the MUF was falling. The “hot spot” showing 111 MHz MUF had been over 160 MHz several minutes earlier, during the time I was working Florida from Maine. Note that this hot spot is at approximate path mid point for those QSOs. This is from https://www.dxmaps.com/
Another very useful tool for spotting potential two meter Es openings is to set up your own MUF monitor in the FM broadcast band. Years ago I had a receiver which I left tuned to a frequency around 90 MHz during the Es season. When I started hearing distant signals exhibiting the strength and fading characteristics common to Es, I would move it to around 107 MHz and keep tuning around that high end of the band. Whenever I heard Es signals there, I would start calling CQ on two meters. The system served quite well for catching these rare openings. These days a wide slice of the FM broadcast band could be visually monitored with a SDR. I would highly recommend this to anyone wanting to work these rare openings on two meters.
I have uploaded audio recordings from this opening to audioBoom:
Two meter contacts made by N1BUG on the evening of June 13, 2017