Sunday, Mar 14, 2010 at 18:49
Radio propagation is almost a science in itself. But I will simplify a lot of it that may help you understand why you may hear someone and they cannot hear you. I will not go near the advantages and shortcomings of antennas. That is another topic.
Consider a station transmitting from
Alice Springs. The time is noon.
The ionosphere is a layer around the earth that acts as a "rough" mirror to radio signals. The time of day and frequency affects how a signal is reflected. Some go straight through and into deep space. Others get trapped in the layer and don't pop out until thousands
miles away. Thus sending Auckland taxis to
Sydney addresses. This is NOT A MYTH.
It is also not a perfect mirror and sometimes if you hear a signal that has been reflected and call back your signal may end up on a different reflected path and miss the base station completely.
That's what you experienced in your example. The antennas can also make a big difference. The best you can do for mobile is get a good wet (!!!!) earth and just try again. I do not know if 4WD HF'ers are permitted to put up wire antennas but if you are, then using a wire dipole or even a fence pointing in the best direction can help. I tried a fence once in 1983 and spoke to a California station using only 1.5 watts on 28 Mhz.
The rule of thumb for picking HF frequencies is: at night use lower frequencies. This is mainly why at night we hear more fishing boats. Note for overseas contacts it depends on what the ionosphere is doing between the two locations.
I hope this helps
Phil
Note: I had to contact Tasmania from
Melbourne for a particular award and after trying for several months we finally succeeded by pointing our antennas (big beams) directly away from each other and went the "long way round". We had to be careful of the time of day along that whole track as
well. Got there and we both got the award.
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