How to work 3B7C: Bands and Propagation

Many DXpeditions nowadays run propagation forecasts for the major geographic areas, and post them on the DXpedition Website. 3B7C is no exception.

But if you live elsewhere in the world, or want to run some much more specific predictions for your own QTH, there are plenty of propagation prediction software packages available which allow you to do it yourself.

Follow some of the links at the end of this article for some good examples.

Rest assured that the 3B7C team themselves have done similar analyses and will be aware of where their beams should be pointing on any given band and at any given time. Almost certainly, the easiest bands on which to look for your first QSOs with the expedition are going to be 20, 17 and 15m. As the sunspots start to reduce in number, openings on the highest bands become less frequent, while the low bands are always a tougher challenge, with greater absorption and higher noise levels.

Of course, most serious DXers have gain antennas for 20, 15 and 10m; often a triband Yagi or even stacked monobanders. So even on those bands you may well have to wait your turn for a QSO (the good news is that 3B7C will be active for two full weeks and three weekends). Far fewer DXers have gain antennas for 30, 17, and 12m, so 17m may well be an excellent band on which to focus to make that first 3B7C QSO (or, indeed, to chase other DXpeditions).

This highlights one of the dilemmas facing the would-be HF operator. With nine HF bands available, not to mention the VHF bands, how on earth can you put up an effective antenna system to cover them all? Unless you live on a farm, the answer is probably “no way”.

This is why low-profile multiband antennas such as trapped verticals or the G5RV are so popular but, inevitably, they are a compromise. It’s often forgotten, for example, that when Louis Varney G5RV came up with his ground-breaking antenna design, not only did the WARC bands not exist, but neither did 15m. And in no way was the antenna expected to present a resistive 50-ohm load to the transmitter but, in those days of valve PA’s, it didn’t really matter! Modern solid-state rigs may behave differently, and reduce power in the face of what they see as a mismatch.

Web Resources
DX Lab (includes PropView)
DX Summit (DX spots)
DX Zone (List of propagation prediction programs)
VOAcap Download
W6EL Propagation Software